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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/10060-0.txt b/10060-0.txt new file mode 100644 index 0000000..2f0438b --- /dev/null +++ b/10060-0.txt @@ -0,0 +1,9535 @@ +*** START OF THE PROJECT GUTENBERG EBOOK 10060 *** + + DISCOURSES: + + BIOLOGICAL & GEOLOGICAL + + ESSAYS + + BY + + THOMAS H. HUXLEY + + 1894 + + + +PREFACE + + +The contents of the present volume, with three exceptions, are either +popular lectures, or addresses delivered to scientific bodies with which +I have been officially connected. I am not sure which gave me the more +trouble. For I have not been one of those fortunate persons who are able +to regard a popular lecture as a mere _hors d'oeuvre_, unworthy of being +ranked among the serious efforts of a philosopher; and who keep their +fame as scientific hierophants unsullied by attempts--at least of the +successful sort--to be understanded of the people. + +On the contrary, I found that the task of putting the truths learned in +the field, the laboratory and the museum, into language which, without +bating a jot of scientific accuracy shall be generally intelligible, +taxed such scientific and literary faculty as I possessed to the +uttermost; indeed my experience has furnished me with no better +corrective of the tendency to scholastic pedantry which besets all those +who are absorbed in pursuits remote from the common ways of men, and +become habituated to think and speak in the technical dialect of their +own little world, as if there were no other. + +If the popular lecture thus, as I believe, finds one moiety of its +justification in the self-discipline of the lecturer, it surely finds the +other half in its effect on the auditory. For though various sadly +comical experiences of the results of my own efforts have led me to +entertain a very moderate estimate of the purely intellectual value of +lectures; though I venture to doubt if more than one in ten of an average +audience carries away an accurate notion of what the speaker has been +driving at; yet is that not equally true of the oratory of the hustings, +of the House of Commons, and even of the pulpit? + +Yet the children of this world are wise in their generation; and both the +politician and the priest are justified by results. The living voice has +an influence over human action altogether independent of the intellectual +worth of that which it utters. Many years ago, I was a guest at a great +City dinner. A famous orator, endowed with a voice of rare flexibility +and power; a born actor, ranging with ease through every part, from +refined comedy to tragic unction, was called upon to reply to a toast. +The orator was a very busy man, a charming conversationalist and by no +means despised a good dinner; and, I imagine, rose without having given a +thought to what he was going to say. The rhythmic roll of sound was +admirable, the gestures perfect, the earnestness impressive; nothing was +lacking save sense and, occasionally, grammar. When the speaker sat down +the applause was terrific and one of my neighbours was especially +enthusiastic. So when he had quieted down, I asked him what the orator +had said. And he could not tell me. + +That sagacious person John Wesley, is reported to have replied to some +one who questioned the propriety of his adaptation of sacred words to +extremely secular airs, that he did not see why the Devil should be left +in possession of all the best tunes. And I do not see why science should +not turn to account the peculiarities of human nature thus exploited by +other agencies: all the more because science, by the nature of its being, +cannot desire to stir the passions, or profit by the weaknesses, of human +nature. The most zealous of popular lecturers can aim at nothing more +than the awakening of a sympathy for abstract truth, in those who do not +really follow his arguments; and of a desire to know more and better in +the few who do. + +At the same time it must be admitted that the popularization of science, +whether by lecture or essay, has its drawbacks. Success in this +department has its perils for those who succeed. The "people who fail" +take their revenge, as we have recently had occasion to observe, by +ignoring all the rest of a man's work and glibly labelling him a more +popularizer. If the falsehood were not too glaring, they would say the +same of Faraday and Helmholtz and Kelvin. + +On the other hand, of the affliction caused by persons who think that +what they have picked up from popular exposition qualifies them for +discussing the great problems of science, it may be said, as the Radical +toast said of the power of the Crown in bygone days, that it "has +increased, is increasing, and ought to be diminished." The oddities of +"English as she is spoke" might be abundantly paralleled by those of +"Science as she is misunderstood" in the sermon, the novel, and the +leading article; and a collection of the grotesque travesties of +scientific conceptions, in the shape of essays on such trifles as "the +Nature of Life" and the "Origin of All Things," which reach me, from time +to time, might well be bound up with them. + + +The tenth essay in this volume unfortunately brought me, I will not say +into collision, but into a position of critical remonstrance with regard +to some charges of physical heterodoxy, brought by my distinguished +friend Lord Kelvin, against British Geology. As President of the +Geological Society of London at that time (1869), I thought I might +venture to plead that we were not such heretics as we seemed to be; and +that, even if we were, recantation would not affect the question of +evolution. + +I am glad to see that Lord Kelvin has just reprinted his reply to my +plea,[1] and I refer the reader to it. I shall not presume to question +anything, that on such ripe consideration, Lord Kelvin has to say upon +the physical problems involved. But I may remark that no one can have +asserted more strongly than I have done, the necessity of looking to +physics and mathematics, for help in regard to the earliest history of +the globe. (See pp. 108 and 109 of this volume.) + +[Footnote 1: _Popular Lectures and Addresses._ II. Macmillan and Co. +1894.] + +And I take the opportunity of repeating the opinion, that, whether what +we call geological time has the lower limit assigned to it by Lord +Kelvin, or the higher assumed by other philosophers; whether the germs of +all living things have originated in the globe itself, or whether they +have been imported on, or in, meteorites from without, the problem of the +origin of those successive Faunae and Florae of the earth, the existence of +which is fully demonstrated by paleontology remains exactly where it was. + +For I think it will be admitted, that the germs brought to us by +meteorites, if any, were not ova of elephants, nor of crocodiles; not +cocoa-nuts nor acorns; not even eggs of shell-fish and corals; but only +those of the lowest forms of animal and vegetable life. Therefore, since +it is proved that, from a very remote epoch of geological time, the earth +has been peopled by a continual succession of the higher forms of animals +and plants, these either must have been created, or they have arisen by +evolution. And in respect of certain groups of animals, the well- +established facts of paleontology leave no rational doubt that they arose +by the latter method. + +In the second place, there are no data whatever, which justify the +biologist in assigning any, even approximately definite, period of time, +either long or short, to the evolution of one species from another by the +process of variation and selection. In the ninth of the following essays, +I have taken pains to prove that the change of animals has gone on at +very different rates in different groups of living beings; that some +types have persisted with little change from the paleozoic epoch till +now, while others have changed rapidly within the limits of an epoch. In +1862 (see below p. 303, 304) in 1863 (vol. II., p. 461) and again in 1864 +(ibid., p. 89-91) I argued, not as a matter of speculation, but, from +paleontological facts, the bearing of which I believe, up to that time, +had not been shown, that any adequate hypothesis of the causes of +evolution must be consistent with progression, stationariness and +retrogression, of the same type at different epochs; of different types +in the same epoch; and that Darwin's hypothesis fulfilled these +conditions. + +According to that hypothesis, two factors are at work, variation and +selection. Next to nothing is known of the causes of the former process; +nothing whatever of the time required for the production of a certain +amount of deviation from the existing type. And, as respects selection, +which operates by extinguishing all but a small minority of variations, +we have not the slightest means of estimating the rapidity with which it +does its work. All that we are justified in saying is that the rate at +which it takes place may vary almost indefinitely. If the famous paint- +root of Florida, which kills white pigs but not black ones, were abundant +and certain in its action, black pigs might be substituted for white in +the course of two or three years. If, on the other hand, it was rare and +uncertain in action, the white pigs might linger on for centuries. + +T.H. HUXLEY. + +HODESLEA, EASTBOURNE, + +_April, 1894._ + + + +CONTENTS + + +I + +ON A PIECE OF CHALK [1868] +(A Lecture delivered to the working men of Norwich during the meeting of +the British Association.) + + +II + +THE PROBLEMS OF THE DEEP SEA [1878] + + +III + +ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. "CHALLENGER" [1875] + + +IV + +YEAST [1871] + + +V + +ON THE FORMATION OF COAL [1870] +(A Lecture delivered at the Philosophical Institute, Bradford.) + + +VI + +ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS +[1876] +(A Friday evening Lecture delivered at the Royal Institution.) + + +VII + +A LOBSTER; OR, THE STUDY OF ZOOLOGY [1861] +(A Lecture delivered at the South Kensington Museum.) + + +VIII + +BIOGENESIS AND ABIOGENESIS [1870] +(The Presidential Address to the Meeting of the British Association for +the Advancement of Science at Liverpool.) + + +IX + +GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE [1862] +(Address to the Geological Society on behalf of the President by one of +the Secretaries.) + + +X + +GEOLOGICAL REFORM [1869] +(Presidential Address to the Geological Society.) + + +XI + +PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION [1870] +(Presidential Address to the Geological Society.) + + + +I + + +ON A PIECE OF CHALK + +[1868] + +If a well were sunk at our feet in the midst of the city of Norwich, the +diggers would very soon find themselves at work in that white substance +almost too soft to be called rock, with which we are all familiar as +"chalk." + +Not only here, but over the whole county of Norfolk, the well-sinker +might carry his shaft down many hundred feet without coming to the end of +the chalk; and, on the sea-coast, where the waves have pared away the +face of the land which breasts them, the scarped faces of the high cliffs +are often wholly formed of the same material. Northward, the chalk may be +followed as far as Yorkshire; on the south coast it appears abruptly in +the picturesque western bays of Dorset, and breaks into the Needles of +the Isle of Wight; while on the shores of Kent it supplies that long line +of white cliffs to which England owes her name of Albion. + +Were the thin soil which covers it all washed away, a curved band of +white chalk, here broader, and there narrower, might be followed +diagonally across England from Lulworth in Dorset, to Flamborough Head in +Yorkshire--a distance of over 280 miles as the crow flies. From this band +to the North Sea, on the east, and the Channel, on the south, the chalk +is largely hidden by other deposits; but, except in the Weald of Kent and +Sussex, it enters into the very foundation of all the south-eastern +counties. + +Attaining, as it does in some places, a thickness of more than a thousand +feet, the English chalk must be admitted to be a mass of considerable +magnitude. Nevertheless, it covers but an insignificant portion of the +whole area occupied by the chalk formation of the globe, much of which +has the same general characters as ours, and is found in detached +patches, some less, and others more extensive, than the English. Chalk +occurs in north-west Ireland; it stretches over a large part of France,-- +the chalk which underlies Paris being, in fact, a continuation of that of +the London basin; it runs through Denmark and Central Europe, and extends +southward to North Africa; while eastward, it appears in the Crimea and +in Syria, and may be traced as far as the shores of the Sea of Aral, in +Central Asia. If all the points at which true chalk occurs were +circumscribed, they would lie within an irregular oval about 3,000 miles +in long diameter--the area of which would be as great as that of Europe, +and would many times exceed that of the largest existing inland sea--the +Mediterranean. + +Thus the chalk is no unimportant element in the masonry of the earth's +crust, and it impresses a peculiar stamp, varying with the conditions to +which it is exposed, on the scenery of the districts in which it occurs. +The undulating downs and rounded coombs, covered with sweet-grassed turf, +of our inland chalk country, have a peacefully domestic and mutton- +suggesting prettiness, but can hardly be called either grand or +beautiful. But on our southern coasts, the wall-sided cliffs, many +hundred feet high, with vast needles and pinnacles standing out in the +sea, sharp and solitary enough to serve as perches for the wary +cormorant, confer a wonderful beauty and grandeur upon the chalk +headlands. And, in the East, chalk has its share in the formation of some +of the most venerable of mountain ranges, such as the Lebanon. + +What is this wide-spread component of the surface of the earth? and +whence did it come? + + +You may think this no very hopeful inquiry. You may not unnaturally +suppose that the attempt to solve such problems as these can lead to no +result, save that of entangling the inquirer in vague speculations, +incapable of refutation and of verification. If such were really the +case, I should have selected some other subject than a "piece of chalk" +for my discourse. But, in truth, after much deliberation, I have been +unable to think of any topic which would so well enable me to lead you to +see how solid is the foundation upon which some of the most startling +conclusions of physical science rest. + +A great chapter of the history of the world is written in the chalk. Few +passages in the history of man can be supported by such an overwhelming +mass of direct and indirect evidence as that which testifies to the truth +of the fragment of the history of the globe, which I hope to enable you +to read, with your own eyes, to-night. Let me add, that few chapters of +human history have a more profound significance for ourselves. I weigh my +words well when I assert, that the man who should know the true history +of the bit of chalk which every carpenter carries about in his breeches- +pocket, though ignorant of all other history, is likely, if he will think +his knowledge out to its ultimate results, to have a truer, and therefore +a better, conception of this wonderful universe, and of man's relation to +it, than the most learned student who is deep-read in the records of +humanity and ignorant of those of Nature. + +The language of the chalk is not hard to learn, not nearly so hard as +Latin, if you only want to get at the broad features of the story it has +to tell; and I propose that we now set to work to spell that story out +together. + +We all know that if we "burn" chalk the result is quicklime. Chalk, in +fact, is a compound of carbonic acid gas, and lime, and when you make it +very hot the carbonic acid flies away and the lime is left. By this +method of procedure we see the lime, but we do not see the carbonic acid. +If, on the other hand, you were to powder a little chalk and drop it into +a good deal of strong vinegar, there would be a great bubbling and +fizzing, and, finally, a clear liquid, in which no sign of chalk would +appear. Here you see the carbonic acid in the bubbles; the lime, +dissolved in the vinegar, vanishes from sight. There are a great many +other ways of showing that chalk is essentially nothing but carbonic acid +and quicklime. Chemists enunciate the result of all the experiments which +prove this, by stating that chalk is almost wholly composed of "carbonate +of lime." + +It is desirable for us to start from the knowledge of this fact, though +it may not seem to help us very far towards what we seek. For carbonate +of lime is a widely-spread substance, and is met with under very various +conditions. All sorts of limestones are composed of more or less pure +carbonate of lime. The crust which is often deposited by waters which +have drained through limestone rocks, in the form of what are called +stalagmites and stalactites, is carbonate of lime. Or, to take a more +familiar example, the fur on the inside of a tea-kettle is carbonate of +lime; and, for anything chemistry tells us to the contrary, the chalk +might be a kind of gigantic fur upon the bottom of the earth-kettle, +which is kept pretty hot below. + +Let us try another method of making the chalk tell us its own history. To +the unassisted eye chalk looks simply like a very loose and open kind of +stone. But it is possible to grind a slice of chalk down so thin that you +can see through it--until it is thin enough, in fact, to be examined with +any magnifying power that may be thought desirable. A thin slice of the +fur of a kettle might be made in the same way. If it were examined +microscopically, it would show itself to be a more or less distinctly +laminated mineral substance, and nothing more. + +But the slice of chalk presents a totally different appearance when +placed under the microscope. The general mass of it is made up of very +minute granules; but, imbedded in this matrix, are innumerable bodies, +some smaller and some larger, but, on a rough average, not more than a +hundredth of an inch in diameter, having a well-defined shape and +structure. A cubic inch of some specimens of chalk may contain hundreds +of thousands of these bodies, compacted together with incalculable +millions of the granules. + +The examination of a transparent slice gives a good notion of the manner +in which the components of the chalk are arranged, and of their relative +proportions. But, by rubbing up some chalk with a brush in water and then +pouring off the milky fluid, so as to obtain sediments of different +degrees of fineness, the granules and the minute rounded bodies may be +pretty well separated from one another, and submitted to microscopic +examination, either as opaque or as transparent objects. By combining the +views obtained in these various methods, each of the rounded bodies may +be proved to be a beautifully-constructed calcareous fabric, made up of a +number of chambers, communicating freely with one another. The chambered +bodies are of various forms. One of the commonest is something like a +badly-grown raspberry, being formed of a number of nearly globular +chambers of different sizes congregated together. It is called +_Globigerina_, and some specimens of chalk consist of little else than +_Globigerinoe_ and granules. Let us fix our attention upon the +_Globigerina_. It is the spoor of the game we are tracking. If we can +learn what it is and what are the conditions of its existence, we shall +see our way to the origin and past history of the chalk. + +A suggestion which may naturally enough present itself is, that these +curious bodies are the result of some process of aggregation which has +taken place in the carbonate of lime; that, just as in winter, the rime +on our windows simulates the most delicate and elegantly arborescent +foliage--proving that the mere mineral water may, under certain +conditions, assume the outward form of organic bodies--so this mineral +substance, carbonate of lime, hidden away in the bowels of the earth, has +taken the shape of these chambered bodies. I am not raising a merely +fanciful and unreal objection. Very learned men, in former days, have +even entertained the notion that all the formed things found in rocks are +of this nature; and if no such conception is at present held to be +admissible, it is because long and varied experience has now shown that +mineral matter never does assume the form and structure we find in +fossils. If any one were to try to persuade you that an oyster-shell +(which is also chiefly composed of carbonate of lime) had crystallized +out of sea-water, I suppose you would laugh at the absurdity. Your +laughter would be justified by the fact that all experience tends to show +that oyster-shells are formed by the agency of oysters, and in no other +way. And if there were no better reasons, we should be justified, on like +grounds, in believing that _Globigerina_ is not the product of anything +but vital activity. + +Happily, however, better evidence in proof of the organic nature of the +_Globigerinoe_ than that of analogy is forthcoming. It so happens that +calcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk, +are being formed, at the present moment, by minute living creatures, +which flourish in multitudes, literally more numerous than the sands of +the sea-shore, over a large extent of that part of the earth's surface +which is covered by the ocean. + +The history of the discovery of these living _Globigerinoe_, and of the +part which they play in rock building, is singular enough. It is a +discovery which, like others of no less scientific importance, has +arisen, incidentally, out of work devoted to very different and +exceedingly practical interests. When men first took to the sea, they +speedily learned to look out for shoals and rocks; and the more the +burthen of their ships increased, the more imperatively necessary it +became for sailors to ascertain with precision the depth of the waters +they traversed. Out of this necessity grew the use of the lead and +sounding line; and, ultimately, marine-surveying, which is the recording +of the form of coasts and of the depth of the sea, as ascertained by the +sounding-lead, upon charts. + +At the same time, it became desirable to ascertain and to indicate the +nature of the sea-bottom, since this circumstance greatly affects its +goodness as holding ground for anchors. Some ingenious tar, whose name +deserves a better fate than the oblivion into which it has fallen, +attained this object by "arming" the bottom of the lead with a lump of +grease, to which more or less of the sand or mud, or broken shells, as +the case might be, adhered, and was brought to the surface. But, however +well adapted such an apparatus might be for rough nautical purposes, +scientific accuracy could not be expected from the armed lead, and to +remedy its defects (especially when applied to sounding in great depths) +Lieut. Brooke, of the American Navy, some years ago invented a most +ingenious machine, by which a considerable portion of the superficial +layer of the sea-bottom can be scooped out and brought up from any depth +to which the lead descends. In 1853, Lieut. Brooke obtained mud from the +bottom of the North Atlantic, between Newfoundland and the Azores, at a +depth of more than 10,000 feet, or two miles, by the help of this +sounding apparatus. The specimens were sent for examination to Ehrenberg +of Berlin, and to Bailey of West Point, and those able microscopists +found that this deep-sea mud was almost entirely composed of the +skeletons of living organisms--the greater proportion of these being just +like the _Globigerinoe_ already known to occur in the chalk. + +Thus far, the work had been carried on simply in the interests of +science, but Lieut. Brooke's method of sounding acquired a high +commercial value, when the enterprise of laying down the telegraph-cable +between this country and the United States was undertaken. For it became +a matter of immense importance to know, not only the depth of the sea +over the whole line along which the cable was to be laid, but the exact +nature of the bottom, so as to guard against chances of cutting or +fraying the strands of that costly rope. The Admiralty consequently +ordered Captain Dayman, an old friend and shipmate of mine, to ascertain +the depth over the whole line of the cable, and to bring back specimens +of the bottom. In former days, such a command as this might have sounded +very much like one of the impossible things which the young Prince in the +Fairy Tales is ordered to do before he can obtain the hand of the +Princess. However, in the months of June and July, 1857, my friend +performed the task assigned to him with great expedition and precision, +without, so far as I know, having met with any reward of that kind. The +specimens or Atlantic mud which he procured were sent to me to be +examined and reported upon.[1] + +[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings in the +North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S. +"Cyclops_." Published by order of the Lords Commissioners of the +Admiralty, 1858. They have since formed the subject of an elaborate +Memoir by Messrs. Parker and Jones, published in the _Philosophical +Transactions_ for 1865.] + +The result of all these operations is, that we know the contours and the +nature of the surface-soil covered by the North Atlantic for a distance +of 1,700 miles from east to west, as well as we know that of any part of +the dry land. It is a prodigious plain--one of the widest and most even +plains in the world. If the sea were drained off, you might drive a +waggon all the way from Valentia, on the west coast of Ireland, to +Trinity Bay, in Newfoundland. And, except upon one sharp incline about +200 miles from Valentia, I am not quite sure that it would even be +necessary to put the skid on, so gentle are the ascents and descents upon +that long route. From Valentia the road would lie down-hill for about 200 +miles to the point at which the bottom is now covered by 1,700 fathoms of +sea-water. Then would come the central plain, more than a thousand miles +wide, the inequalities of the surface of which would be hardly +perceptible, though the depth of water upon it now varies from 10,000 to +15,000 feet; and there are places in which Mont Blanc might be sunk +without showing its peak above water. Beyond this, the ascent on the +American side commences, and gradually leads, for about 300 miles, to the +Newfoundland shore. + +Almost the whole of the bottom of this central plain (which extends for +many hundred miles in a north and south direction) is covered by a fine +mud, which, when brought to the surface, dries into a greyish white +friable substance. You can write with this on a blackboard, if you are so +inclined; and, to the eye, it is quite like very soft, grayish chalk. +Examined chemically, it proves to be composed almost wholly of carbonate +of lime; and if you make a section of it, in the same way as that of the +piece of chalk was made, and view it with the microscope, it presents +innumerable _Globigerinoe_ embedded in a granular matrix. Thus this deep- +sea mud is substantially chalk. I say substantially, because there are a +good many minor differences; but as these have no bearing on the question +immediately before us,--which is the nature of the _Globigerinoe_ of the +chalk,--it is unnecessary to speak of them. + +_Globigerinoe_ of every size, from the smallest to the largest, are +associated together in the Atlantic mud, and the chambers of many are +filled by a soft animal matter. This soft substance is, in fact, the +remains of the creature to which the _Globigerinoe_ shell, or rather +skeleton, owes its existence--and which is an animal of the simplest +imaginable description. It is, in fact, a mere particle of living jelly, +without defined parts of any kind--without a mouth, nerves, muscles, or +distinct organs, and only manifesting its vitality to ordinary +observation by thrusting out and retracting from all parts of its +surface, long filamentous processes, which serve for arms and legs. Yet +this amorphous particle, devoid of everything which, in the higher +animals, we call organs, is capable of feeding, growing, and multiplying; +of separating from the ocean the small proportion of carbonate of lime +which is dissolved in sea-water; and of building up that substance into a +skeleton for itself, according to a pattern which can be imitated by no +other known agency. + +The notion that animals can live and flourish in the sea, at the vast +depths from which apparently living _Globigerinoe_; have been brought up, +does not agree very well with our usual conceptions respecting the +conditions of animal life; and it is not so absolutely impossible as it +might at first sight appear to be, that the _Globigcrinoe_ of the +Atlantic sea-bottom do not live and die where they are found. + +As I have mentioned, the soundings from the great Atlantic plain are +almost entirely made up of _Globigerinoe_, with the granules which have +been mentioned, and some few other calcareous shells; but a small +percentage of the chalky mud--perhaps at most some five per cent. of it-- +is of a different nature, and consists of shells and skeletons composed +of silex, or pure flint. These silicious bodies belong partly to the +lowly vegetable organisms which are called _Diatomaceoe_, and partly to +the minute, and extremely simple, animals, termed _Radiolaria_. It is +quite certain that these creatures do not live at the bottom of the +ocean, but at its surface--where they may be obtained in prodigious +numbers by the use of a properly constructed net. Hence it follows that +these silicious organisms, though they are not heavier than the lightest +dust, must have fallen, in some cases, through fifteen thousand feet of +water, before they reached their final resting-place on the ocean floor. +And considering how large a surface these bodies expose in proportion to +their weight, it is probable that they occupy a great length of time in +making their burial journey from the surface of the Atlantic to the +bottom. + +But if the _Radiolaria_ and Diatoms are thus rained upon the bottom of +the sea, from the superficial layer of its waters in which they pass +their lives, it is obviously possible that the _Globigerinoe_ may be +similarly derived; and if they were so, it would be much more easy to +understand how they obtain their supply of food than it is at present. +Nevertheless, the positive and negative evidence all points the other +way. The skeletons of the full-grown, deep-sea _Globigerinoe_ are so +remarkably solid and heavy in proportion to their surface as to seem +little fitted for floating; and, as a matter of fact, they are not to be +found along with the Diatoms and _Radiolaria_ in the uppermost stratum of +the open ocean. It has been observed, again, that the abundance of +_Globigerinoe_, in proportion to other organisms, of like kind, increases +with the depth of the sea; and that deep-water _Globigerinoe_ are larger +than those which live in shallower parts of the sea; and such facts +negative the supposition that these organisms have been swept by currents +from the shallows into the deeps of the Atlantic. It therefore seems to +be hardly doubtful that these wonderful creatures live and die at the +depths in which they are found.[2] + +[Footnote 2: During the cruise of H.M.S. _Bulldog_, commanded by Sir +Leopold M'Clintock, in 1860, living star-fish were brought up, clinging +to the lowest part of the sounding-line, from a depth of 1,260 fathoms, +midway between Cape Farewell, in Greenland, and the Rockall banks. Dr. +Wallich ascertained that the sea-bottom at this point consisted of the +ordinary _Globigerina_ ooze, and that the stomachs of the star-fishes +were full of _Globigerinoe_. This discovery removes all objections to the +existence of living _Globigerinoe_ at great depths, which are based upon +the supposed difficulty of maintaining animal life under such conditions; +and it throws the burden of proof upon those who object to the +supposition that the _Globigerinoe_ live and die where they are found.] + +However, the important points for us are, that the living _Globigerinoe_ +are exclusively marine animals, the skeletons of which abound at the +bottom of deep seas; and that there is not a shadow of reason for +believing that the habits of the _Globigerinoe_ of the chalk differed +from those of the existing species. But if this be true, there is no +escaping the conclusion that the chalk itself is the dried mud of an +ancient deep sea. + +In working over the soundings collected by Captain Dayman, I was +surprised to find that many of what I have called the "granules" of that +mud were not, as one might have been tempted to think at first, the more +powder and waste of _Globigerinoe_, but that they had a definite form and +size. I termed these bodies "_coccoliths_," and doubted their organic +nature. Dr. Wallich verified my observation, and added the interesting +discovery that, not unfrequently, bodies similar to these "coccoliths" +were aggregated together into spheroids, which lie termed +"_coccospheres_." So far as we knew, these bodies, the nature of which is +extremely puzzling and problematical, were peculiar to the Atlantic +soundings. But, a few years ago, Mr. Sorby, in making a careful +examination of the chalk by means of thin sections and otherwise, +observed, as Ehrenberg had done before him, that much of its granular +basis possesses a definite form. Comparing these formed particles with +those in the Atlantic soundings, he found the two to be identical; and +thus proved that the chalk, like the surroundings, contains these +mysterious coccoliths and coccospheres. Here was a further and most +interesting confirmation, from internal evidence, of the essential +identity of the chalk with modern deep-sea mud. _Globigerinoe_, +coccoliths, and coccospheres are found as the chief constituents of both, +and testify to the general similarity of the conditions under which both +have been formed.[3] + +[Footnote 3: I have recently traced out the development of the +"coccoliths" from a diameter of 1/7000th of an inch up to their largest +size (which is about 1/1000th), and no longer doubt that they are +produced by independent organisms, which, like the _Globigerinoe_, live +and die at the bottom of the sea.] + +The evidence furnished by the hewing, facing, and superposition of the +stones of the Pyramids, that these structures were built by men, has no +greater weight than the evidence that the chalk was built by +_Globigerinoe_; and the belief that those ancient pyramid-builders were +terrestrial and air-breathing creatures like ourselves, is not better +based than the conviction that the chalk-makers lived in the sea. But as +our belief in the building of the Pyramids by men is not only grounded on +the internal evidence afforded by these structures, but gathers strength +from multitudinous collateral proofs, and is clinched by the total +absence of any reason for a contrary belief; so the evidence drawn from +the _Globigerinoe_ that the chalk is an ancient sea-bottom, is fortified +by innumerable independent lines of evidence; and our belief in the truth +of the conclusion to which all positive testimony tends, receives the +like negative justification from the fact that no other hypothesis has a +shadow of foundation. + +It may be worth while briefly to consider a few of these collateral +proofs that the chalk was deposited at the bottom of the sea. The great +mass of the chalk is composed, as we have seen, of the skeletons of +_Globigerinoe_, and other simple organisms, imbedded in granular matter. +Here and there, however, this hardened mud of the ancient sea reveals the +remains of higher animals which have lived and died, and left their hard +parts in the mud, just as the oysters die and leave their shells behind +them, in the mud of the present seas. + +There are, at the present day, certain groups of animals which are never +found in fresh waters, being unable to live anywhere but in the sea. Such +are the corals; those corallines which are called _Polyzoa_; those +creatures which fabricate the lamp-shells, and are called _Brachiopoda_; +the pearly _Nautilus_, and all animals allied to it; and all the forms of +sea-urchins and star-fishes. Not only are all these creatures confined to +salt water at the present day; but, so far as our records of the past go, +the conditions of their existence have been the same: hence, their +occurrence in any deposit is as strong evidence as can be obtained, that +that deposit was formed in the sea. Now the remains of animals of all the +kinds which have been enumerated, occur in the chalk, in greater or less +abundance; while not one of those forms of shell-fish which are +characteristic of fresh water has yet been observed in it. + +When we consider that the remains of more than three thousand distinct +species of aquatic animals have been discovered among the fossils of the +chalk, that the great majority of them are of such forms as are now met +with only in the sea, and that there is no reason to believe that any one +of them inhabited fresh water--the collateral evidence that the chalk +represents an ancient sea-bottom acquires as great force as the proof +derived from the nature of the chalk itself. I think you will now allow +that I did not overstate my case when I asserted that we have as strong +grounds for believing that all the vast area of dry land, at present +occupied by the chalk, was once at the bottom of the sea, as we have for +any matter of history whatever; while there is no justification for any +other belief. + +No less certain it is that the time during which the countries we now +call south-east England, France, Germany, Poland, Russia, Egypt, Arabia, +Syria, were more or less completely covered by a deep sea, was of +considerable duration. We have already seen that the chalk is, in places, +more than a thousand feet thick. I think you will agree with me, that it +must have taken some time for the skeletons of animalcules of a hundredth +of an inch in diameter to heap up such a mass as that. I have said that +throughout the thickness of the chalk the remains of other animals are +scattered. These remains are often in the most exquisite state of +preservation. The valves of the shell-fishes are commonly adherent; the +long spines of some of the sea-urchins, which would be detached by the +smallest jar, often remain in their places. In a word, it is certain that +these animals have lived and died when the place which they now occupy +was the surface of as much of the chalk as had then been deposited; and +that each has been covered up by the layer of _Globigerina_ mud, upon +which the creatures imbedded a little higher up have, in like manner, +lived and died. But some of these remains prove the existence of reptiles +of vast size in the chalk sea. These lived their time, and had their +ancestors and descendants, which assuredly implies time, reptiles being +of slow growth. + +There is more curious evidence, again, that the process of covering up, +or, in other words, the deposit of _Globigerina_ skeletons, did not go on +very fast. It is demonstrable that an animal of the cretaceous sea might +die, that its skeleton might lie uncovered upon the sea-bottom long +enough to lose all its outward coverings and appendages by putrefaction; +and that, after this had happened, another animal might attach itself to +the dead and naked skeleton, might grow to maturity, and might itself die +before the calcareous mud had buried the whole. + +Cases of this kind are admirably described by Sir Charles Lyell. He +speaks of the frequency with which geologists find in the chalk a +fossilized sea-urchin, to which is attached the lower valve of a +_Crania_. This is a kind of shell-fish, with a shell composed of two +pieces, of which, as in the oyster, one is fixed and the other free. + +"The upper valve is almost invariably wanting, though occasionally found +in a perfect state of preservation in the white chalk at some distance. +In this case, we see clearly that the sea-urchin first lived from youth +to age, then died and lost its spines, which were carried away. Then the +young _Crania_ adhered to the bared shell, grew and perished in its turn; +after which, the upper valve was separated from the lower, before the +Echinus became enveloped in chalky mud."[4] + +A specimen in the Museum of Practical Geology, in London, still further +prolongs the period which must have elapsed between the death of the sea- +urchin, and its burial by the _Globigerinoe_. For the outward face of the +valve of a _Crania_, which is attached to a sea-urchin, (_Micraster_), is +itself overrun by an incrusting coralline, which spreads thence over more +or less of the surface of the sea-urchin. It follows that, after the +upper valve of the _Crania_ fell off, the surface of the attached valve +must have remained exposed long enough to allow of the growth of the +whole coralline, since corallines do not live embedded in mud.[4] + +[Footnote 4: _Elements of Geology_, by Sir Charles Lyell, Bart. F.B.S., +p. 23.] + +The progress of knowledge may, one day, enable us to deduce from such +facts as these the maximum rate at which the chalk can have accumulated, +and thus to arrive at the minimum duration of the chalk period. Suppose +that the valve of the _Cronia_ upon which a coralline has fixed itself in +the way just described, is so attached to the sea-urchin that no part of +it is more than an inch above the face upon which the sea-urchin rests. +Then, as the coralline could not have fixed itself, if the _Crania_ had +been covered up with chalk mud, and could not have lived had itself been +so covered, it follows, that an inch of chalk mud could not have +accumulated within the time between the death and decay of the soft parts +of the sea-urchin and the growth of the coralline to the full size which +it has attained. If the decay of the soft parts of the sea-urchin; the +attachment, growth to maturity, and decay of the _Crania_; and the +subsequent attachment and growth of the coralline, took a year (which is +a low estimate enough), the accumulation of the inch of chalk must have +taken more than a year: and the deposit of a thousand feet of chalk must, +consequently, have taken more than twelve thousand years. + +The foundation of all this calculation is, of course, a knowledge of the +length of time the _Crania_ and the coralline needed to attain their full +size; and, on this head, precise knowledge is at present wanting. But +there are circumstances which tend to show, that nothing like an inch of +chalk has accumulated during the life of a _Crania_; and, on any probable +estimate of the length of that life, the chalk period must have had a +much longer duration than that thus roughly assigned to it. + +Thus, not only is it certain that the chalk is the mud of an ancient sea- +bottom; but it is no less certain, that the chalk sea existed during an +extremely long period, though we may not be prepared to give a precise +estimate of the length of that period in years. The relative duration is +clear, though the absolute duration may not be definable. The attempt to +affix any precise date to the period at which the chalk sea began, or +ended, its existence, is baffled by difficulties of the same kind. But +the relative age of the cretaceous epoch may be determined with as great +ease and certainty as the long duration of that epoch. + +You will have heard of the interesting discoveries recently made, in +various parts of Western Europe, of flint implements, obviously worked +into shape by human hands, under circumstances which show conclusively +that man is a very ancient denizen of these regions. It has been proved +that the whole populations of Europe, whose existence has been revealed +to us in this way, consisted of savages, such as the Esquimaux are now; +that, in the country which is now France, they hunted the reindeer, and +were familiar with the ways of the mammoth and the bison. The physical +geography of France was in those days different from what it is now--the +river Somme, for instance, having cut its bed a hundred feet deeper +between that time and this; and, it is probable, that the climate was +more like that of Canada or Siberia, than that of Western Europe. + +The existence of these people is forgotten even in the traditions of the +oldest historical nations. The name and fame of them had utterly vanished +until a few years back; and the amount of physical change which has been +effected since their day renders it more than probable that, venerable as +are some of the historical nations, the workers of the chipped flints of +Hoxne or of Amiens are to them, as they are to us, in point of antiquity. +But, if we assign to these hoar relics of long-vanished generations of +men the greatest age that can possibly be claimed for them, they are not +older than the drift, or boulder clay, which, in comparison with the +chalk, is but a very juvenile deposit. You need go no further than your +own sea-board for evidence of this fact. At one of the most charming +spots on the coast of Norfolk, Cromer, you will see the boulder clay +forming a vast mass, which lies upon the chalk, and must consequently +have come into existence after it. Huge boulders of chalk are, in fact, +included in the clay, and have evidently been brought to the position +they now occupy by the same agency as that which has planted blocks of +syenite from Norway side by side with them. + +The chalk, then, is certainly older than the boulder clay. If you ask how +much, I will again take you no further than the same spot upon your own +coasts for evidence. I have spoken of the boulder clay and drift as +resting upon the chalk. That is not strictly true. Interposed between the +chalk and the drift is a comparatively insignificant layer, containing +vegetable matter. But that layer tells a wonderful history. It is full of +stumps of trees standing as they grew. Fir-trees are there with their +cones, and hazel-bushes with their nuts; there stand the stools of oak +and yew trees, beeches and alders. Hence this stratum is appropriately +called the "forest-bed." + +It is obvious that the chalk must have been upheaved and converted into +dry land, before the timber trees could grow upon it. As the bolls of +some of these trees are from two to three feet in diameter, it is no less +clear that the dry land thus formed remained in the same condition for +long ages. And not only do the remains of stately oaks and well-grown +firs testify to the duration of this condition of things, but additional +evidence to the same effect is afforded by the abundant remains of +elephants, rhinoceroses, hippopotamuses, and other great wild beasts, +which it has yielded to the zealous search of such men as the Rev. Mr. +Gunn. When you look at such a collection as he has formed, and bethink +you that these elephantine bones did veritably carry their owners about, +and these great grinders crunch, in the dark woods of which the forest- +bed is now the only trace, it is impossible not to feel that they are as +good evidence of the lapse of time as the annual rings of the tree +stumps. + +Thus there is a writing upon the wall of cliffs at Cromer, and whoso runs +may read it. It tells us, with an authority which cannot be impeached, +that the ancient sea-bed of the chalk sea was raised up, and remained dry +land, until it was covered with forest, stocked with the great game the +spoils of which have rejoiced your geologists. How long it remained in +that condition cannot be said; but "the whirligig of time brought its +revenges" in those days as in these. That dry land, with the bones and +teeth of generations of long-lived elephants, hidden away among the +gnarled roots and dry leaves of its ancient trees, sank gradually to the +bottom of the icy sea, which covered it with huge masses of drift and +boulder clay. Sea-beasts, such as the walrus, now restricted to the +extreme north, paddled about where birds had twittered among the topmost +twigs of the fir-trees. How long this state of things endured we know +not, but at length it came to an end. The upheaved glacial mud hardened +into the soil of modern Norfolk. Forests grew once more, the wolf and the +beaver replaced the reindeer and the elephant; and at length what we call +the history of England dawned. + +Thus you have, within the limits of your own county, proof that the chalk +can justly claim a very much greater antiquity than even the oldest +physical traces of mankind. But we may go further and demonstrate, by +evidence of the same authority as that which testifies to the existence +of the father of men, that the chalk is vastly older than Adam himself. +The Book of Genesis informs us that Adam, immediately upon his creation, +and before the appearance of Eve, was placed in the Garden of Eden. The +problem of the geographical position of Eden has greatly vexed the +spirits of the learned in such matters, but there is one point respecting +which, so far as I know, no commentator has ever raised a doubt. This is, +that of the four rivers which are said to run out of it, Euphrates and +Hiddekel are identical with the rivers now known by the names of +Euphrates and Tigris. But the whole country in which these mighty rivers +take their origin, and through which they run, is composed of rocks which +are either of the same age as the chalk, or of later date. So that the +chalk must not only have been formed, but, after its formation, the time +required for the deposit of these later rocks, and for their upheaval +into dry land, must have elapsed, before the smallest brook which feeds +the swift stream of "the great river, the river of Babylon," began to +flow. + + +Thus, evidence which cannot be rebutted, and which need not be +strengthened, though if time permitted I might indefinitely increase its +quantity, compels you to believe that the earth, from the time of the +chalk to the present day, has been the theatre of a series of changes as +vast in their amount, as they were slow in their progress. The area on +which we stand has been first sea and then land, for at least four +alternations; and has remained in each of these conditions for a period +of great length. + +Nor have these wonderful metamorphoses of sea into land, and of land into +sea, been confined to one corner of England. During the chalk period, or +"cretaceous epoch," not one of the present great physical features of the +globe was in existence. Our great mountain ranges, Pyrenees, Alps, +Himalayas, Andes, have all been upheaved since the chalk was deposited, +and the cretaceous sea flowed over the sites of Sinai and Ararat. All +this is certain, because rocks of cretaceous, or still later, date have +shared in the elevatory movements which gave rise to these mountain +chains; and may be found perched up, in some cases, many thousand feet +high upon their flanks. And evidence of equal cogency demonstrates that, +though, in Norfolk, the forest-bed rests directly upon the chalk, yet it +does so, not because the period at which the forest grew immediately +followed that at which the chalk was formed, but because an immense lapse +of time, represented elsewhere by thousands of feet of rock, is not +indicated at Cromer. + +I must ask you to believe that there is no less conclusive proof that a +still more prolonged succession of similar changes occurred, before the +chalk was deposited. Nor have we any reason to think that the first term +in the series of these changes is known. The oldest sea-beds preserved to +us are sands, and mud, and pebbles, the wear and tear of rocks which were +formed in still older oceans. + +But, great as is the magnitude of these physical changes of the world, +they have been accompanied by a no less striking series of modifications +in its living inhabitants. All the great classes of animals, beasts of +the field, fowls of the air, creeping things, and things which dwell in +the waters, flourished upon the globe long ages before the chalk was +deposited. Very few, however, if any, of these ancient forms of animal +life were identical with those which now live. Certainly not one of the +higher animals was of the same species as any of those now in existence. +The beasts of the field, in the days before the chalk, were not our +beasts of the field, nor the fowls of the air such as those which the eye +of men has seen flying, unless his antiquity dates infinitely further +back than we at present surmise. If we could be carried back into those +times, we should be as one suddenly set down in Australia before it was +colonized. We should see mammals, birds, reptiles, fishes, insects, +snails, and the like, clearly recognizable as such, and yet not one of +them would be just the same as those with which we are familiar, and many +would be extremely different. + +From that time to the present, the population of the world has undergone +slow and gradual, but incessant, changes. There has been no grand +catastrophe--no destroyer has swept away the forms of life of one period, +and replaced them by a totally new creation: but one species has vanished +and another has taken its place; creatures of one type of structure have +diminished, those of another have increased, as time has passed on. And +thus, while the differences between the living creatures of the time +before the chalk and those of the present day appear startling, if placed +side by side, we are led from one to the other by the most gradual +progress, if we follow the course of Nature through the whole series of +those relics of her operations which she has left behind. It is by the +population of the chalk sea that the ancient and the modern inhabitants +of the world are most completely connected. The groups which are dying +out flourish, side by side, with the groups which are now the dominant +forms of life. Thus the chalk contains remains of those strange flying +and swimming reptiles, the pterodactyl, the ichthyosaurus, and the +plesiosaurus, which are found in no later deposits, but abounded in +preceding ages. The chambered shells called ammonites and belemnites, +which are so characteristic of the period preceding the cretaceous, in +like manner die with it. + +But, amongst these fading remainders of a previous state of things, are +some very modern forms of life, looking like Yankee pedlars among a tribe +of Red Indians. Crocodiles of modern type appear; bony fishes, many of +them very similar to existing species, almost supplant the forms of fish +which predominate in more ancient seas; and many kinds of living shell- +fish first become known to us in the chalk. The vegetation acquires a +modern aspect. A few living animals are not even distinguishable as +species, from those which existed at that remote epoch. The _Globigerina_ +of the present day, for example, is not different specifically from that +of the chalk; and the same maybe said of many other _Foraminifera_. I +think it probable that critical and unprejudiced examination will show +that more than one species of much higher animals have had a similar +longevity; but the only example which I can at present give confidently +is the snake's-head lampshell (_Terebratulina caput serpentis_), which +lives in our English seas and abounded (as _Terebratulina striata_ of +authors) in the chalk. + +The longest line of human ancestry must hide its diminished head before +the pedigree of this insignificant shell-fish. We Englishmen are proud to +have an ancestor who was present at the Battle of Hastings. The ancestors +of _Terebratulina caput serpentis_ may have been present at a battle of +_Ichthyosauria_ in that part of the sea which, when the chalk was +forming, flowed over the site of Hastings. While all around has changed, +this _Terebratulina_ has peacefully propagated its species from +generation to generation, and stands to this day, as a living testimony +to the continuity of the present with the past history of the globe. + + +Up to this moment I have stated, so far as I know, nothing but well- +authenticated facts, and the immediate conclusions which they force upon +the mind. But the mind is so constituted that it does not willingly rest +in facts and immediate causes, but seeks always after a knowledge of the +remoter links in the chain of causation. + +Taking the many changes of any given spot of the earth's surface, from +sea to land and from land to sea, as an established fact, we cannot +refrain from asking ourselves how these changes have occurred. And when +we have explained them--as they must be explained--by the alternate slow +movements of elevation and depression which have affected the crust of +the earth, we go still further back, and ask, Why these movements? + +I am not certain that any one can give you a satisfactory answer to that +question. Assuredly I cannot. All that can be said, for certain, is, that +such movements are part of the ordinary course of nature, inasmuch as +they are going on at the present time. Direct proof may be given, that +some parts of the land of the northern hemisphere are at this moment +insensibly rising and others insensibly sinking; and there is indirect, +but perfectly satisfactory, proof, that an enormous area now covered by +the Pacific has been deepened thousands of feet, since the present +inhabitants of that sea came into existence. Thus there is not a shadow +of a reason for believing that the physical changes of the globe, in past +times, have been effected by other than natural causes. Is there any more +reason for believing that the concomitant modifications in the forms of +the living inhabitants of the globe have been brought about in other +ways? + +Before attempting to answer this question, let us try to form a distinct +mental picture of what has happened in some special case. The crocodiles +are animals which, as a group, have a very vast antiquity. They abounded +ages before the chalk was deposited; they throng the rivers in warm +climates, at the present day. There is a difference in the form of the +joints of the back-bone, and in some minor particulars, between the +crocodiles of the present epoch and those which lived before the chalk; +but, in the cretaceous epoch, as I have already mentioned, the crocodiles +had assumed the modern type of structure. Notwithstanding this, the +crocodiles of the chalk are not identically the same as those which lived +in the times called "older tertiary," which succeeded the cretaceous +epoch; and the crocodiles of the older tertiaries are not identical with +those of the newer tertiaries, nor are these identical with existing +forms. I leave open the question whether particular species may have +lived on from epoch to epoch. But each epoch has had its peculiar +crocodiles; though all, since the chalk, have belonged to the modern +type, and differ simply in their proportions, and in such structural +particulars as are discernible only to trained eyes. + +How is the existence of this long succession of different species of +crocodiles to be accounted for? Only two suppositions seem to be open to +us--Either each species of crocodile has been specially created, or it +has arisen out of some pre-existing form by the operation of natural +causes. Choose your hypothesis; I have chosen mine. I can find no +warranty for believing in the distinct creation of a score of successive +species of crocodiles in the course of countless ages of time. Science +gives no countenance to such a wild fancy; nor can even the perverse +ingenuity of a commentator pretend to discover this sense, in the simple +words in which the writer of Genesis records the proceedings of the fifth +and six days of the Creation. + +On the other hand, I see no good reason for doubting the necessary +alternative, that all these varied species have been evolved from pre- +existing crocodilian forms, by the operation of causes as completely a +part of the common order of nature as those which have effected the +changes of the inorganic world. Few will venture to affirm that the +reasoning which applies to crocodiles loses its force among other +animals, or among plants. If one series of species has come into +existence by the operation of natural causes, it seems folly to deny that +all may have arisen in the same way. + +A small beginning has led us to a great ending. If I were to put the bit +of chalk with which we started into the hot but obscure flame of burning +hydrogen, it would presently shine like the sun. It seems to me that this +physical metamorphosis is no false image of what has been the result of +our subjecting it to a jet of fervent, though nowise brilliant, thought +to-night. It has become luminous, and its clear rays, penetrating the +abyss of the remote past, have brought within our ken some stages of the +evolution of the earth. And in the shifting "without haste, but without +rest" of the land and sea, as in the endless variation of the forms +assumed by living beings, we have observed nothing but the natural +product of the forces originally possessed by the substance of the +universe. + + + +II + + +THE PROBLEMS OF THE DEEP SEA + +[1873] + +On the 21st of December, 1872, H.M.S. _Challenger_, an eighteen gun +corvette, of 2,000 tons burden, sailed from Portsmouth harbour for a +three, or perhaps four, years' cruise. No man-of-war ever left that +famous port before with so singular an equipment. Two of the eighteen +sixty-eight pounders of the _Challenger's_ armament remained to enable +her to speak with effect to sea-rovers, haply devoid of any respect for +science, in the remote seas for which she is bound; but the main-deck +was, for the most part, stripped of its war-like gear, and fitted up with +physical, chemical, and biological laboratories; Photography had its dark +cabin; while apparatus for dredging, trawling, and sounding; for +photometers and for thermometers, filled the space formerly occupied by +guns and gun-tackle, pistols and cutlasses. + +The crew of the _Challenger_ match her fittings. Captain Nares, his +officers and men, are ready to look after the interests of hydrography, +work the ship, and, if need be, fight her as seamen should; while there +is a staff of scientific civilians, under the general direction of Dr. +Wyville Thomson, F.R.S. (Professor of Natural History in Edinburgh +University by rights, but at present detached for duty _in partibus_), +whose business it is to turn all the wonderfully packed stores of +appliances to account, and to accumulate, before the ship returns to +England, such additions to natural knowledge as shall justify the labour +and cost involved in the fitting out and maintenance of the expedition. + +Under the able and zealous superintendence of the Hydrographer, Admiral +Richards, every precaution which experience and forethought could devise +has been taken to provide the expedition with the material conditions of +success; and it would seem as if nothing short of wreck or pestilence, +both most improbable contingencies, could prevent the _Challenger_ from +doing splendid work, and opening up a new era in the history of +scientific voyages. + +The dispatch of this expedition is the culmination of a series of such +enterprises, gradually increasing in magnitude and importance, which the +Admiralty, greatly to its credit, has carried out for some years past; +and the history of which is given by Dr. Wyville Thomson in the +beautifully illustrated volume entitled "The Depths of the Sea," +published since his departure. + +"In the spring of the year 1868, my friend Dr. W.B. Carpenter, at that +time one of the Vice-Presidents of the Royal Society, was with me in +Ireland, where we were working out together the structure and development +of the Crinoids. I had long previously had a profound conviction that the +land of promise for the naturalist, the only remaining region where there +were endless novelties of extraordinary interest ready to the hand which +had the means of gathering them, was the bottom of the deep sea. I had +even had a glimpse of some of these treasures, for I had seen, the year +before, with Prof. Sars, the forms which I have already mentioned dredged +by his son at a depth of 300 to 400 fathoms off the Loffoten Islands. I +propounded my views to my fellow-labourer, and we discussed the subject +many times over our microscopes. I strongly urged Dr. Carpenter to use +his influence at head-quarters to induce the Admiralty, probably through +the Council of the Royal Society, to give us the use of a vessel properly +fitted with dredging gear and all necessary scientific apparatus, that +many heavy questions as to the state of things in the depths of the +ocean, which were still in a state of uncertainty, might be definitely +settled. After full consideration, Dr. Carpenter promised his hearty co- +operation, and we agreed that I should write to him on his return to +London, indicating generally the results which I anticipated, and +sketching out what I conceived to be a promising line of inquiry. The +Council of the Royal Society warmly supported the proposal; and I give +here in chronological order the short and eminently satisfactory +correspondence which led to the Admiralty placing at the disposal of Dr. +Carpenter and myself the gunboat _Lightninq_, under the command of Staff- +Commander May, R.N., in the summer of 1868, for a trial cruise to the +North of Scotland, and afterwards to the much wider surveys in H.M.S. +_Porcupine_, Captain Calver, R.N., which were made with the additional +association of Mr. Gwyn Jeffreys, in the summers of the years 1869 and +1870."[1] + +[Footnote 1: The Depths of the Sea, pp. 49-50.] + +Plain men may be puzzled to understand why Dr. Wyville Thomson, not being +a cynic, should relegate the "Land of Promise" to the bottom of the deep +sea, they may still more wonder what manner of "milk and honey" the +_Challenger_ expects to find; and their perplexity may well rise to its +maximum, when they seek to divine the manner in which that milk and honey +are to be got out of so inaccessible a Canaan. I will, therefore, +endeavour to give some answer to these questions in an order the reverse +of that in which I have stated them. + +Apart from hooks, and lines, and ordinary nets, fishermen have, from time +immemorial, made use of two kinds of implements for getting at sea- +creatures which live beyond tide-marks--these are the "dredge" and the +"trawl." The dredge is used by oyster-fishermen. Imagine a large bag, the +mouth of which has the shape of an elongated parallelogram, and is +fastened to an iron frame of the same shape, the two long sides of this +rim being fashioned into scrapers. Chains attach the ends of the frame to +a stout rope, so that when the bag is dragged along by the rope the edge +of one of the scrapers rests on the ground, and scrapes whatever it +touches into the bag. The oyster-dredger takes one of these machines in +his boat, and when he has reached the oyster-bed the dredge is tossed +overboard; as soon as it has sunk to the bottom the rope is paid out +sufficiently to prevent it from pulling the dredge directly upwards, and +is then made fast while the boat goes ahead. The dredge is thus dragged +along and scrapes oysters and other sea-animals and plants, stones, and +mud into the bag. When the dredger judges it to be full he hauls it up, +picks out the oysters, throws the rest overboard, and begins again. + +Dredging in shallow water, say ten to twenty fathoms, is an easy +operation enough; but the deeper the dredger goes, the heavier must be +his vessel, and the stouter his tackle, while the operation of hauling up +becomes more and more laborious. Dredging in 150 fathoms is very hard +work, if it has to be carried on by manual labour; but by the use of the +donkey-engine to supply power,[2] and of the contrivances known as +"accumulators," to diminish the risk of snapping the dredge rope by the +rolling and pitching of the vessel, the dredge has been worked deeper and +deeper, until at last, on the 22nd of July, 1869, H.M.S. _Porcupine_ +being in the Bay of Biscay, Captain Calver, her commander, performed the +unprecedented feat of dredging in 2,435 fathoms, or 14,610 feet, a depth +nearly equal to the height of Mont Blanc. The dredge "was rapidly hauled +on deck at one o'clock in the morning of the 23rd, after an absence of +7-1/4 hours, and a journey of upwards of eight statute miles," with a +hundred weight and a half of solid contents. + +[Footnote 2: The emotional side of the scientific nature has its +singularities. Many persons will call to mind a certain philosopher's +tenderness over his watch--"the little creature"--which was so singularly +lost and found again. But Dr. Wyville Thomson surpasses the owner of the +watch in his loving-kindness towards a donkey-engine. "This little engine +was the comfort of our lives. Once or twice it was overstrained, and then +we pitied the willing little thing, panting like an overtaxed horse."] + +The trawl is a sort of net for catching those fish which habitually live +at the bottom of the sea, such as soles, plaice, turbot, and gurnett. The +mouth of the net may be thirty or forty feet wide, and one edge of its +mouth is fastened to a beam of wood of the same length. The two ends of +the beam are supported by curved pieces of iron, which raise the beam and +the edge of the net which is fastened to it, for a short distance, while +the other edge of the mouth of the net trails upon the ground. The closed +end of the net has the form of a great pouch; and, as the beam is dragged +along, the fish, roused from the bottom by the sweeping of the net, +readily pass into its mouth and accumulate in the pouch at its end. After +drifting with the tide for six or seven hours the trawl is hauled up, the +marketable fish are picked out, the others thrown away, and the trawl +sent overboard for another operation. + +More than a thousand sail of well-found trawlers are constantly engaged +in sweeping the seas around our coast in this way, and it is to them that +we owe a very large proportion of our supply of fish. The difficulty of +trawling, like that of dredging, rapidly increases with the depth at +which the operation is performed; and, until the other day, it is +probable that trawling at so great a depth as 100 fathoms was something +unheard of. But the first news from the _Challenger_ opens up new +possibilities for the trawl. + +Dr. Wyville Thomson writes ("Nature," March 20, 1873):-- + +"For the first two or three hauls in very deep water off the coast of +Portugal, the dredge came up filled with the usual 'Atlantic ooze,' +tenacious and uniform throughout, and the work of hours, in sifting, gave +the very smallest possible result. We were extremely anxious to get some +idea of the general character of the Fauna, and particularly of the +distribution of the higher groups; and after various suggestions for +modification of the dredge, it was proposed to try the ordinary trawl. We +had a compact trawl, with a 15-feet beam, on board, and we sent it down +off Cape St. Vincent at a depth of 600 fathoms. The experiment looked +hazardous, but, to our great satisfaction, the trawl came up all right +and contained, with many of the larger invertebrate, several fishes.... +After the first attempt we tried the trawl several times at depths of +1090, 1525, and, finally, 2125 fathoms, and always with success." + +To the coral-fishers of the Mediterranean, who seek the precious red +coral, which grows firmly fixed to rocks at a depth of sixty to eighty +fathoms, both the dredge and the trawl would be useless. They, therefore, +have recourse to a sort of frame, to which are fastened long bundles of +loosely netted hempen cord, and which is lowered by a rope to the depth +at which the hempen cords can sweep over the surface of the rocks and +break off the coral, which is brought up entangled in the cords. A +similar contrivance has arisen out of the necessities of deep-sea +exploration. + +In the course of the dredging of the _Porcupine_, it was frequently found +that, while few objects of interest were brought up within the dredge, +many living creatures came up sticking to the outside of the dredge-bag, +and even to the first few fathoms of the dredge-rope. The mouth of the +dredge doubtless rapidly filled with mud, and thus the things it should +have brought up were shut out. To remedy this inconvenience Captain +Calver devised an arrangement not unlike that employed by the coral- +fishers. He fastened half a dozen swabs, such as are used for drying +decks, to the dredge. A swab is something like what a birch-broom would +be if its twigs were made of long, coarse, hempen yarns. These dragged +along after the dredge over the surface of the mud, and entangled the +creatures living there--multitudes of which, twisted up in the strands of +the swabs, were brought to the surface with the dredge. A further +improvement was made by attaching a long iron bar to the bottom of the +dredge bag, and fastening large bunches of teased-out hemp to the end of +this bar. These "tangles" bring up immense quantities of such animals as +have long arms, or spines, or prominences which readily become caught in +the hemp, but they are very destructive to the fragile organisms which +they imprison; and, now that the trawl can be successfully worked at the +greatest depths, it may be expected to supersede them; at least, wherever +the ground is soft enough to permit of trawling. + +It is obvious that between the dredge, the trawl, and the tangles, there +is little chance for any organism, except such as are able to burrow +rapidly, to remain safely at the bottom of any part of the sea which the +_Challenger_ undertakes to explore. And, for the first time in the +history of scientific exploration, we have a fair chance of learning what +the population of the depths of the sea is like in the most widely +different parts of the world. + +And now arises the next question. The means of exploration being fairly +adequate, what forms of life may be looked for at these vast depths? + +The systematic study of the Distribution of living beings is the most +modern branch of Biological Science, and came into existence long after +Morphology and Physiology had attained a considerable development. This +naturally does not imply that, from the time men began to observe natural +phenomena, they were ignorant of the fact that the animals and plants of +one part of the world are different from those in other regions; or that +those of the hills are different from those of the plains in the same +region; or finally that some marine creatures are found only in the +shallows, while others inhabit the deeps. Nevertheless, it was only after +the discovery of America that the attention of naturalists was powerfully +drawn to the wonderful differences between the animal population of the +central and southern parts of the new world and that of those parts of +the old world which lie under the same parallels of latitude. So far back +as 1667 Abraham Mylius, in his treatise "De Animalium origine et +migratione, populorum," argues that, since there are innumerable species +of animals in America which do not exist elsewhere, they must have been +made and placed there by the Deity: Buffon no less forcibly insists upon +the difference between the Faunae of the old and new world. But the first +attempt to gather facts of this order into a whole, and to coordinate +them into a series of generalizations, or laws of Geographical +Distribution, is not a century old, and is contained in the "Specimen +Zoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens," +published, in 1777, by the learned Brunswick Professor, Eberhard +Zimmermann, who illustrates his work by what he calls a "Tabula +Zoographica," which is the oldest distributional map known to me. + +In regard to matters of fact, Zimmermann's chief aim is to show that +among terrestrial mammals, some occur all over the world, while others +are restricted to particular areas of greater or smaller extent; and that +the abundance of species follows temperature, being greatest in warm and +least in cold climates. But marine animals, he thinks, obey no such law. +The Arctic and Atlantic seas, he says, are as full of fishes and other +animals as those of the tropics. It is, therefore, clear that cold does +not affect the dwellers in the sea as it does land animals, and that this +must be the case follows from the fact that sea water, "propter varias +quas continet bituminis spiritusque particulas," freezes with much more +difficulty than fresh water. On the other hand, the heat of the +Equatorial sun penetrates but a short distance below the surface of the +ocean. Moreover, according to Zimmermann, the incessant disturbance of +the mass of the sea by winds and tides, so mixes up the warm and the cold +that life is evenly diffused and abundant throughout the ocean. + +In 1810, Risso, in his work on the Ichthyology of Nice, laid the +foundation of what has since been termed "bathymetrical" distribution, or +distribution in depth, by showing that regions of the sea bottom of +different depths could be distinguished by the fishes which inhabit them. +There was the _littoral region_ between tide marks with its sand-eels, +pipe fishes, and blennies: the _seaweed region_, extending from low- +water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish; +and the _deep-sea region_, from 450 feet to 1500 feet or more, with +its file-fish, sharks, gurnards, cod, and sword-fish. + +More than twenty years later, M.M. Audouin and Milne Edwards carried out +the principle of distinguishing the Faunae of different zones of depth +much more minutely, in their "Recherches pour servir à l'Histoire +Naturelle du Littoral de la France," published in 1832. + +They divide the area included between highwater-mark and lowwater-mark of +spring tides (which is very extensive, on account of the great rise and +fall of the tide on the Normandy coast about St. Malo, where their +observations were made) into four zones, each characterized by its +peculiar invertebrate inhabitants. Beyond the fourth region they +distinguish a fifth, which is never uncovered, and is inhabited by +oysters, scallops, and large starfishes and other animals. Beyond this +they seem to think that animal life is absent.[3] + +[Footnote 3: "Enfin plus has encore, c'est-à -dire alors loin des côtes, +le fond des eaux ne paraît plus être habité, du moms dans nos mers, par +aucun de ces animaux" (1. c. tom. i. p. 237). The "ces animaux" leaves +the meaning of the authors doubtful.] + +Audouin and Milne Edwards were the first to see the importance of the +bearing of a knowledge of the manner in which marine animals are +distributed in depth, on geology. They suggest that, by this means, it +will be possible to judge whether a fossiliferous stratum was formed upon +the shore of an ancient sea, and even to determine whether it was +deposited in shallower or deeper water on that shore; the association of +shells of animals which live in different zones of depth will prove that +the shells have been transported into the position in which they are +found; while, on the other hand, the absence of shells in a deposit will +not justify the conclusion that the waters in which it was formed were +devoid of animal inhabitants, inasmuch as they might have been only too +deep for habitation. + +The new line of investigation thus opened by the French naturalists was +followed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our own +country, in 1840,[4] and by Oersted, in Denmark, a few years later. The +genius of Forbes, combined with his extensive knowledge of botany, +invertebrate zoology, and geology, enabled him to do more than any of his +compeers, in bringing the importance of distribution in depth into +notice; and his researches in the Aegean Sea, and still more his +remarkable paper "On the Geological Relations of the existing Fauna and +Flora of the British Isles," published in 1846, in the first volume of +the "Memoirs of the Geological Survey of Great Britain," attracted +universal attention. + +[Footnote 4: In the paper in the _Memoirs of the Survey_ cited further +on, Forbes writes:-- + +"In an essay 'On the Association of Mollusca on the British Coasts, +considered with reference to Pleistocene Geology,' printed in [the +_Edinburgh Academic Annual_ for] 1840, I described the mollusca, as +distributed on our shores and seas, in four great zones or regions, +usually denominated 'The Littoral zone,' 'The region of Laminariae,' 'The +region of Coral-lines,' and 'The region of Corals.' An extensive series +of researches, chiefly conducted by the members of the committee +appointed by the British Association to investigate the marine geology of +Britain by means of the dredge, have not invalidated this classification, +and the researches of Professor Lovén, in the Norwegian and Lapland seas, +have borne out their correctness The first two of the regions above +mentioned had been previously noticed by Lamoureux, in his account of the +distribution (vertically) of sea-weeds, by Audouin and Milne Edwards in +their _Observations on the Natural History of the coast of France_, and +by Sars in the preface to his _Beskrivelser og Jagttayelser_."] + +On the coasts of the British Islands, Forbes distinguishes four zones or +regions, the Littoral (between tide marks), the Laminarian (between +lowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), and +the Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms). +But, in the deeper waters of the Aegean Sea, between the shore and a depth +of 300 fathoms, Forbes was able to make out no fewer than eight zones of +life, in the course of which the number and variety of forms gradually +diminished until, beyond 300 fathoms, life disappeared altogether. Hence +it appeared as if descent in the sea had much the same effect on life, as +ascent on land. Recent investigations appear to show that Forbes was +right enough in his classification of the facts of distribution in depth +as they are to be observed in the Aegean; and though, at the time he +wrote, one or two observations were extant which might have warned him +not to generalize too extensively from his Aegean experience, his own +dredging work was so much more extensive and systematic than that of any +other naturalist, that it is not wonderful he should have felt justified +in building upon it. Nevertheless, so far as the limit of the range of +life in depth goes, Forbes' conclusion has been completely negatived, and +the greatest depths yet attained show not even an approach to a "zero of +life":-- + +"During the several cruises of H.M. ships _Lightning_ and _Porcupine_ in +the years 1868, 1869, and 1870," says Dr. Wyville Thomson, "fifty-seven +hauls of the dredge were taken in the Atlantic at depths beyond 500 +fathoms, and sixteen at depths beyond 1,000 fathoms, and, in all cases, +life was abundant. In 1869, we took two casts in depths greater than +2,000 fathoms. In both of these life was abundant; and with the deepest +cast, 2,435 fathoms, off the month of the Bay of Biscay, we took living, +well-marked and characteristic examples of all the five invertebrate sub- +kingdoms. And thus the question of the existence of abundant animal life +at the bottom of the sea has been finally settled and for all depths, for +there is no reason to suppose that the depth anywhere exceeds between +three and four thousand fathoms; and if there be nothing in the +conditions of a depth of 2,500 fathoms to prevent the full development of +a varied Fauna, it is impossible to suppose that even an additional +thousand fathoms would make any great difference."[5] + +[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind, +obtained by previous observers, are stated at length in the sixth +chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under +the authority of Professor Peirce, the Superintendent of the United +States Coast Survey, in the years 1867, 1868, and 1869, are particularly +noteworthy, and it is probably not too much to say, in the words of +Professor Agassiz, "that we owe to the coast survey the first broad and +comprehensive basis for an exploration of the sea bottom on a large +scale, opening a new era in zoological and geological research."] + +As Dr. Wyville Thomson's recent letter, cited above, shows, the use of +the trawl, at great depths, has brought to light a still greater +diversity of life. Fishes came up from a depth of 600 to more than 1,000 +fathoms, all in a peculiar condition from the expansion of the air +contained in their bodies. On their relief from the extreme pressure, +their eyes, especially, had a singular appearance, protruding like great +globes from their heads. Bivalve and univalve mollusca seem to be rare at +the greatest depths; but starfishes, sea urchins and other echinoderms, +zoophytes, sponges, and protozoa abound. + +It is obvious that the _Challenger_ has the privilege of opening a new +chapter in the history of the living world. She cannot send down her +dredges and her trawls into these virgin depths of the great ocean +without bringing up a discovery. Even though the thing itself may be +neither "rich nor rare," the fact that it came from that depth, in that +particular latitude and longitude, will be a new fact in distribution, +and, as such, have a certain importance. + +But it may be confidently assumed that the things brought up will very +frequently be zoological novelties; or, better still, zoological +antiquities, which, in the tranquil and little-changed depths of the +ocean, have escaped the causes of destruction at work in the shallows, +and represent the predominant population of a past age. + +It has been seen that Audouin and Milne Edwards foresaw the general +influence of the study of distribution in depth upon the interpretation +of geological phenomena. Forbes connected the two orders of inquiry still +more closely; and in the thoughtful essay "On the connection between the +distribution of the existing Fauna and Flora of the British Isles, and +the geological changes which have affected their area, especially during +the epoch of the Northern drift," to which reference has already been +made, he put forth a most pregnant suggestion. + +In certain parts of the sea bottom in the immediate vicinity of the +British Islands, as in the Clyde district, among the Hebrides, in the +Moray Firth, and in the German Ocean, there are depressed areas, forming a +kind of submarine valleys, the centres of which are from 80 to 100 +fathoms, or more, deep. These depressions are inhabited by assemblages of +marine animals, which differ from those found over the adjacent and +shallower region, and resemble those which are met with much farther +north, on the Norwegian coast. Forbes called these Scandinavian +detachments "Northern outliers." + +How did these isolated patches of a northern population get into these +deep places? To explain the mystery, Forbes called to mind the fact that, +in the epoch which immediately preceded the present, the climate was much +colder (whence the name of "glacial epoch" applied to it); and that the +shells which are found fossil, or sub-fossil, in deposits of that age are +precisely such as are now to be met with only in the Scandinavian, or +still more Arctic, regions. Undoubtedly, during the glacial epoch, the +general population of our seas had, universally, the northern aspect +which is now presented only by the "northern outliers"; just as the +vegetation of the land, down to the sea-level, had the northern character +which is, at present, exhibited only by the plants which live on the tops +of our mountains. But, as the glacial epoch passed away, and the present +climatal conditions were developed, the northern plants were able to +maintain themselves only on the bleak heights, on which southern forms +could not compete with them. And, in like manner, Forbes suggested that, +after the glacial epoch, the northern animals then inhabiting the sea +became restricted to the deeps in which they could hold their own against +invaders from the south, better fitted than they to flourish in the +warmer waters of the shallows. Thus depth in the sea corresponded in its +effect upon distribution to height on the land. + +The same idea is applied to the explanation of a similar anomaly in the +Fauna of the Aegean:-- + +"In the deepest of the regions of depth of the Aegean, the representation +of a Northern Fauna is maintained, partly by identical and partly by +representative forms.... The presence of the latter is essentially due to +the law (of representation of parallels of latitude by zones of depth), +whilst that of the former species depended on their transmission from +their parent seas during a former epoch, and subsequent isolation. That +epoch was doubtless the newer Pliocene or Glacial Era, when the _Mya +truncata_ and other northern forms now extinct in the Mediterranean, and +found fossil in the Sicilian tertiaries, ranged into that sea. The +changes which there destroyed the _shallow water_ glacial forms, did not +affect those living in the depths, and which still survive."[6] + +[Footnote 6: _Memoirs of the Geological Survey of Great Britain_, Vol. i. +p. 390.] + +The conception that the inhabitants of local depressions of the sea +bottom might be a remnant of the ancient population of the area, which +had held their own in these deep fastnesses against an invading Fauna, as +Britons and Gaels have held out in Wales and in Scotland against +encroaching Teutons, thus broached by Forbes, received a wider +application than Forbes had dreamed of when the sounding machine first +brought up specimens of the mud of the deep sea. As I have pointed out +elsewhere,[7] it at once became obvious that the calcareous sticky mud of +the Atlantic was made up, in the main, of shells of _Globigerina_ and +other _Foraminifera_, identical with those of which the true chalk is +composed, and the identity extended even to the presence of those +singular bodies, the Coccoliths and Coccospheres, the true nature of +which is not yet made out. Here then were organisms, as old as the +cretaceous epoch, still alive, and doing their work of rock-making at the +bottom of existing seas. What if _Globigerina_ and the Coccoliths should +not be the only survivors of a world passed away, which are hidden +beneath three miles of salt water? The letter which Dr. Wyville Thomson +wrote to Dr. Carpenter in May, 1868, out of which all these expeditions +have grown, shows that this query had become a practical problem in Dr. +Thomson's mind at that time; and the desirableness of solving the problem +is put in the foreground of his reasons for urging the Government to +undertake the work of exploration:-- + +[Footnote 7: See above, "On a Piece of Chalk," p. 13.] + +"Two years ago, M. Sars, Swedish Government Inspector of Fisheries, had +an opportunity, in his official capacity, of dredging off the Loffoten +Islands at a depth of 300 fathoms. I visited Norway shortly after his +return, and had an opportunity of studying with his father, Professor +Sars, some of his results. Animal forms were _abundant_; many of them +were new to science; and among them was one of surpassing interest, the +small crinoid, of which you have a specimen, and which we at once +recognised as a degraded type of the _Apiocrinidoe_, an order hitherto +regarded as extinct, which attained its maximum in the Pear Encrinites of +the Jurassic period, and whose latest representative hitherto known was +the _Bourguettocrinus_ of the chalk. Some years previously, Mr. +Absjornsen, dredging in 200 fathoms in the Hardangerfjord, procured +several examples of a Starfish (_Brisinga_), which seems to find its +nearest ally in the fossil genus _Protaster_. These observations place it +beyond a doubt that animal life is abundant in the ocean at depths +varying from 200 to 300 fathoms, that the forms at these great depths +differ greatly from those met with in ordinary dredgings, and that, at +all events in some cases, these animals are closely allied to, and would +seem to be directly descended from, the Fauna of the early tertiaries. + +"I think the latter result might almost have been anticipated; and, +probably, further investigation will largely add to this class of data, +and will give us an opportunity of testing our determinations of the +zoological position of some fossil types by an examination of the soft +parts of their recent representatives. The main cause of the destruction, +the migration, and the extreme modification of animal types, appear to be +change of climate, chiefly depending upon oscillations of the earth's +crust. These oscillations do not appear to have ranged, in the Northern +portion of the Northern Hemisphere, much beyond 1,000 feet since the +commencement of the Tertiary Epoch. The temperature of deep waters seems +to be constant for all latitudes at 39°; so that an immense area of the +North Atlantic must have had its conditions unaffected by tertiary or +post-tertiary oscillations."[8] + +[Footnote 8: The Depths of the Sea, pp. 51-52.] + +As we shall see, the assumption that the temperature of the deep sea is +everywhere 39° F. (4° Cent.) is an error, which Dr. Wyville Thomson +adopted from eminent physical writers; but the general justice of the +reasoning is not affected by this circumstance, and Dr. Thomson's +expectation has been, to some extent, already verified. + +Thus besides _Globigerina_, there are eighteen species of deep-sea +_Foraminifera_ identical with species found in the chalk. Imbedded in the +chalky mud of the deep sea, in many localities, are innumerable cup- +shaped sponges, provided with six-rayed silicious spicula, so disposed +that the wall of the cup is formed of a lacework of flinty thread. Not +less abundant, in some parts of the chalk formation, are the fossils +known as _Ventriculites_, well described by Dr. Thomson as "elegant vases +or cups, with branching root-like bases, or groups of regularly or +irregularly spreading tubes delicately fretted on the surface with an +impressed network like the finest lace"; and he adds, "When we compare +such recent forms as _Aphrocallistes, Iphiteon, Holtenia_, and +_Askonema_, with certain series of the chalk _Ventriculites_, there +cannot be the slightest doubt that they belong to the same family--in +some cases to very nearly allied genera."[9] + +[Footnote 9: _The Depths of the Sea_, p. 484.] + +Professor Duncan finds "several corals from the coast of Portugal more +nearly allied to chalk forms than to any others." + +The Stalked Crinoids or Feather Stars, so abundant in ancient times, are +now exclusively confined to the deep sea, and the late explorations have +yielded forms of old affinity, the existence of which has hitherto been +unsuspected. The general character of the group of star fishes imbedded +in the white chalk is almost the same as in the modern Fauna of the deep +Atlantic. The sea urchins of the deep sea, while none of them are +specifically identical with any chalk form, belong to the same general +groups, and some closely approach extinct cretaceous genera. + +Taking these facts in conjunction with the positive evidence of the +existence, during the Cretaceous epoch, of a deep ocean where now lies +the dry land of central and southern Europe, northern Africa, and western +and southern Asia; and of the gradual diminution of this ocean during the +older tertiary epoch, until it is represented at the present day by such +teacupfuls as the Caspian, the Black Sea, and the Mediterranean; the +supposition of Dr. Thomson and Dr. Carpenter that what is now the deep +Atlantic, was the deep Atlantic (though merged in a vast easterly +extension) in the Cretaceous epoch, and that the _Globigerina_ mud has +been accumulating there from that time to this, seems to me to have a +great degree of probability. And I agree with Dr. Wyville Thomson against +Sir Charles Lyell (it takes two of us to have any chance against his +authority) in demurring to the assertion that "to talk of chalk having +been uninterruptedly formed in the Atlantic is as inadmissible in a +geographical as in a geological sense." + +If the word "chalk" is to be used as a stratigraphical term and +restricted to _Globigerina_ mud deposited during the Cretaceous epoch, of +course it is improper to call the precisely similar mud of more recent +date, chalk. If, on the other hand, it is to be used as a mineralogical +term, I do not see how the modern and the ancient chalks are to be +separated--and, looking at the matter geographically, I see no reason to +doubt that a boring rod driven from the surface of the mud which forms +the floor of the mid-Atlantic would pass through one continuous mass of +_Globigerina_ mud, first of modern, then of tertiary, and then of +mesozoic date; the "chalks" of different depths and ages being +distinguished merely by the different forms of other organisms associated +with the _Globigerinoe_. + +On the other hand, I think it must be admitted that a belief in the +continuity of the modern with the ancient chalk has nothing to do with +the proposition that we can, in any sense whatever, be said to be still +living in the Cretaceous epoch. When the _Challenger's_ trawl brings up +an _Ichthyosaurus_, along with a few living specimens of _Belemnites_ and +_Turrilites_, it may be admitted that she has come upon a cretaceous +"outlier." A geological period is characterized not only by the presence +of those creatures which lived in it, but by the absence of those which +have only come into existence later; and, however large a proportion of +true cretaceous forms may be discovered in the deep sea, the modern types +associated with them must be abolished before the Fauna, as a whole, +could, with any propriety, be termed Cretaceous. + + +I have now indicated some of the chief lines of Biological inquiry, in +which the _Challenger_ has special opportunities for doing good service, +and in following which she will be carrying out the work already +commenced by the _Lightning_ and _Porcupine_ in their cruises of 1868 and +subsequent years. + +But biology, in the long run, rests upon physics, and the first condition +for arriving at a sound theory of distribution in the deep sea, is the +precise ascertainment of the conditions of life; or, in other words, a +full knowledge of all those phenomena which are embraced under the head +of the Physical Geography of the Ocean. + +Excellent work has already been done in this direction, chiefly under the +superintendence of Dr. Carpenter, by the _Lightning_ and the +_Porcupine_,[10] and some data of fundamental importance to the physical +geography of the sea have been fixed beyond a doubt. + +[Footnote 10: _Proceedings of the Royal Society_, 1870 and 1872] + +Thus, though it is true that sea-water steadily contracts as it cools +down to its freezing point, instead of expanding before it reaches its +freezing point as fresh water does, the truth has been steadily ignored +by even the highest authorities in physical geography, and the erroneous +conclusions deduced from their erroneous premises have been widely +accepted as if they were ascertained facts. Of course, if sea-water, like +fresh water, were heaviest at a temperature of 39° F. and got lighter as +it approached 32° F., the water of the bottom of the deep sea could not +be colder than 39°. But one of the first results of the careful +ascertainment of the temperature at different depths, by means of +thermometers specially contrived for the avoidance of the errors produced +by pressure, was the proof that, below 1000 fathoms in the Atlantic, down +to the greatest depths yet sounded, the water has a temperature always +lower than 38° Fahr., whatever be the temperature of the water at the +surface. And that this low temperature of the deepest water is probably +the universal rule for the depths of the open ocean is shown, among +others, by Captain Chimmo's recent observations in the Indian ocean, +between Ceylon and Sumatra, where, the surface water ranging from 85°-81° +Fahr., the temperature at the bottom, at a depth of 2270 to 2656 fathoms, +was only from 34° to 32° Fahr. + +As the mean temperature of the superficial layer of the crust of the +earth may be taken at about 50° Fahr., it follows that the bottom layer +of the deep sea in temperate and hot latitudes, is, on the average, much +colder than either of the bodies with which it is in contact; for the +temperature of the earth is constant, while that of the air rarely falls +so low as that of the bottom water in the latitudes in question; and even +when it does, has time to affect only a comparatively thin stratum of the +surface water before the return of warm weather. + +How does this apparently anomalous state of things come about? If we +suppose the globe to be covered with a universal ocean, it can hardly be +doubted that the cold of the regions towards the poles must tend to cause +the superficial water of those regions to contract and become +specifically heavier. Under these circumstances, it would have no +alternative but to descend and spread over the sea bottom, while its +place would be taken by warmer water drawn from the adjacent regions. +Thus, deep, cold, polar-equatorial currents, and superficial, warmer, +equatorial-polar currents, would be set up; and as the former would have +a less velocity of rotation from west to east than the regions towards +which they travel, they would not be due southerly or northerly currents, +but south-westerly in the northern hemisphere, and north-westerly in the +southern; while, by a parity of reasoning, the equatorial-polar warm +currents would be north-easterly in the northern hemisphere, and south- +easterly in the southern. Hence, as a north-easterly current has the same +direction as a south-westerly wind, the direction of the northern +equatorial-polar current in the extra-tropical part of its course would +pretty nearly coincide with that of the anti-trade winds. The freezing of +the surface of the polar sea would not interfere with the movement thus +set up. For, however bad a conductor of heat ice may be, the unfrozen +sea-water immediately in contact with the undersurface of the ice must +needs be colder than that further off; and hence will constantly tend to +descend through the subjacent warmer water. + +In this way, it would seem inevitable that the surface waters of the +northern and southern frigid zones must, sooner or later, find their way +to the bottom of the rest of the ocean; and there accumulate to a +thickness dependent on the rate at which they absorb heat from the crust +of the earth below, and from the surface water above. + +If this hypothesis be correct, it follows that, if any part of the ocean +in warm latitudes is shut off from the influence of the cold polar +underflow, the temperature of its deeps should be less cold than the +temperature of corresponding depths in the open sea. Now, in the +Mediterranean, Nature offers a remarkable experimental proof of just the +kind needed. It is a landlocked sea which runs nearly east and west, +between the twenty-ninth and forty-fifth parallels of north latitude. +Roughly speaking, the average temperature of the air over it is 75° Fahr. +in July and 48° in January. + +This great expanse of water is divided by the peninsula of Italy +(including Sicily), continuous with which is a submarine elevation +carrying less than 1,200 feet of water, which extends from Sicily to Cape +Bon in Africa, into two great pools--an eastern and a western. The +eastern pool rapidly deepens to more than 12,000 feet, and sends off to +the north its comparatively shallow branches, the Adriatic and the Aegean +Seas. The western pool is less deep, though it reaches some 10,000 feet. +And, just as the western end of the eastern pool communicates by a +shallow passage, not a sixth of its greatest depth, with the western +pool, so the western pool is separated from the Atlantic by a ridge which +runs between Capes Trafalgar and Spartel, on which there is hardly 1,000 +feet of water. All the water of the Mediterranean which lies deeper than +about 150 fathoms, therefore, is shut off from that of the Atlantic, and +there is no communication between the cold layer of the Atlantic (below +1,000 fathoms) and the Mediterranean. Under these circumstances, what is +the temperature of the Mediterranean? Everywhere below 600 feet it is +about 55° Fahr.; and consequently, at its greatest depths, it is some 20° +warmer than the corresponding depths of the Atlantic. + +It seems extremely difficult to account for this difference in any other +way, than by adopting the views so strongly and ably advocated by Dr. +Carpenter, that, in the existing distribution of land and water, such a +circulation of the water of the ocean does actually occur, as +theoretically must occur, in the universal ocean, with which we started. + +It is quite another question, however, whether this theoretic +circulation, true cause as it may be, is competent to give rise to such +movements of sea-water, in mass, as those currents, which have commonly +been regarded as northern extensions of the Gulf-stream. I shall not +venture to touch upon this complicated problem; but I may take occasion +to remark that the cause of a much simpler phenomenon--the stream of +Atlantic water which sets through the Straits of Gibraltar, eastward, at +the rate of two or three miles an hour or more, does not seem to be so +clearly made out as is desirable. + +The facts appear to be that the water of the Mediterranean is very +slightly denser than that of the Atlantic (1.0278 to 1.0265), and that +the deep water of the Mediterranean is slightly denser than that of the +surface; while the deep water of the Atlantic is, if anything, lighter +than that of the surface. Moreover, while a rapid superficial current is +setting in (always, save in exceptionally violent easterly winds) through +the Straits of Gibraltar, from the Atlantic to the Mediterranean, a deep +undercurrent (together with variable side currents) is setting out +through the Straits, from the Mediterranean to the Atlantic. + +Dr. Carpenter adopts, without hesitation, the view that the cause of this +indraught of Atlantic water is to be sought in the much more rapid +evaporation which takes place from the surface of the Mediterranean than +from that of the Atlantic; and thus, by lowering the level of the former, +gives rise to an indraught from the latter. + +But is there any sound foundation for the three assumptions involved +here? Firstly, that the evaporation from the Mediterranean, as a whole, +is much greater than that from the Atlantic under corresponding +parallels; secondly, that the rainfall over the Mediterranean makes up +for evaporation less than it does over the Atlantic; and thirdly, +supposing these two questions answered affirmatively: Are not these +sources of loss in the Mediterranean fully covered by the prodigious +quantity of fresh water which is poured into it by great rivers and +submarine springs? Consider that the water of the Ebro, the Rhine, the +Po, the Danube, the Don, the Dnieper, and the Nile, all flow directly or +indirectly into the Mediterranean; that the volume of fresh water which +they pour into it is so enormous that fresh water may sometimes be baled +up from the surface of the sea off the Delta of the Nile, while the land +is not yet in sight; that the water of the Black Sea is half fresh, and +that a current of three or four miles an hour constantly streams from it +Mediterraneanwards through the Bosphorus;--consider, in addition, that no +fewer than ten submarine springs of fresh water are known to burst up in +the Mediterranean, some of them so large that Admiral Smyth calls them +"subterranean rivers of amazing volume and force"; and it would seem, on +the face of the matter, that the sun must have enough to do to keep the +level of the Mediterranean down; and that, possibly, we may have to seek +for the cause of the small superiority in saline contents of the +Mediterranean water in some condition other than solar evaporation. + +Again, if the Gibraltar indraught is the effect of evaporation, why does +it go on in winter as well as in summer? + +All these are questions more easily asked than answered; but they must be +answered before we can accept the Gibraltar stream as an example of a +current produced by indraught with any comfort. + +The Mediterranean is not included in the _Challenger's_ route, but she +will visit one of the most promising and little explored of +hydrographical regions--the North Pacific, between Polynesia and the +Asiatic and American shores; and doubtless the store of observations upon +the currents of this region, which she will accumulate, when compared +with what we know of the North Atlantic, will throw a powerful light upon +the present obscurity of the Gulf-stream problem. + + + +III + + +ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. _CHALLLENGER_ + +[1875] + +In May, 1873, I drew attention[1] to the important problems connected +with the physics and natural history of the sea, to the solution of which +there was every reason to hope the cruise of H.M.S. _Challenger_ would +furnish important contributions. The expectation then expressed has not +been disappointed. Reports to the Admiralty, papers communicated to the +Royal Society, and large collections which have already been sent home, +have shown that the _Challenger's_ staff have made admirable use of their +great opportunities; and that, on the return of the expedition in 1874, +their performance will be fully up to the level of their promise. Indeed, +I am disposed to go so far as to say, that if nothing more came of the +_Challengers_ expedition than has hitherto been yielded by her +exploration of the nature of the sea bottom at great depths, a full +scientific equivalent of the trouble and expense of her equipment would +have been obtained. + +[Footnote 1: See the preceding Essay.] + +In order to justify this assertion, and yet, at the same time, not to +claim more for Professor Wyville Thomson and his colleagues than is their +due, I must give a brief history of the observations which have preceded +their exploration of this recondite field of research, and endeavour to +make clear what was the state of knowledge in December, 1872, and what +new facts have been added by the scientific staff of the _Challenger_. So +far as I have been able to discover, the first successful attempt to +bring up from great depths more of the sea bottom than would adhere to a +sounding-lead, was made by Sir John Ross, in the voyage to the Arctic +regions which he undertook in 1818. In the Appendix to the narrative of +that voyage, there will be found an account of a very ingenious apparatus +called "clams"--a sort of double scoop--of his own contrivance, which Sir +John Ross had made by the ship's armourer; and by which, being in +Baffin's Bay, in 72° 30' N. and 77° 15' W., he succeeded in bringing up +from 1,050 fathoms (or 6,300 feet), "several pounds" of a "fine green +mud," which formed the bottom of the sea in this region. Captain (now Sir +Edward) Sabine, who accompanied Sir John Ross on this cruise, says of +this mud that it was "soft and greenish, and that the lead sunk several +feet into it." A similar "fine green mud" was found to compose the sea +bottom in Davis Straits by Goodsir in 1845. Nothing is certainly known of +the exact nature of the mud thus obtained, but we shall see that the mud +of the bottom of the Antarctic seas is described in curiously similar +terms by Dr. Hooker, and there is no doubt as to the composition of this +deposit. + +In 1850, Captain Penny collected in Assistance Bay, in Kingston Bay, and +in Melville Bay, which lie between 73° 45' and 74° 40' N., specimens of +the residuum left by melted surface ice, and of the sea bottom in these +localities. Dr. Dickie, of Aberdeen, sent these materials to Ehrenberg, +who made out[2] that the residuum of the melted ice consisted for the +most part of the silicious cases of diatomaceous plants, and of the +silicious spicula of sponges; while, mixed with these, were a certain +number of the equally silicious skeletons of those low animal organisms, +which were termed _Polycistineoe_ by Ehrenberg, but are now known as +_Radiolaria_. + +[Footnote 2: _Ueber neue Anschauungen des kleinsten nördlichen +Polarlebens_.--Monatsberichte d. K. Akad. Berlin, 1853.] + +In 1856, a very remarkable addition to our knowledge of the nature of the +sea bottom in high northern latitudes was made by Professor Bailey of +West Point. Lieutenant Brooke, of the United States Navy, who was +employed in surveying the Sea of Kamschatka, had succeeded in obtaining +specimens of the sea bottom from greater depths than any hitherto +reached, namely from 2,700 fathoms (16,200 feet) in 56° 46' N., and 168° +18' E.; and from 1,700 fathoms (10,200 feet) in 60° 15' N. and 170° 53' +E. On examining these microscopically, Professor Bailey found, as +Ehrenberg had done in the case of mud obtained on the opposite side of +the Arctic region, that the fine mud was made up of shells of +_Diatomacoe_, of spicula of sponges, and of _Radiolaria_, with a small +admixture of mineral matters, but without a trace of any calcareous +organisms. + +Still more complete information has been obtained concerning the nature +of the sea bottom in the cold zone around the south pole. Between the +years 1839 and 1843, Sir James Clark Ross executed his famous Antarctic +expedition, in the course of which he penetrated, at two widely distant +points of the Antarctic zone, into the high latitudes of the shores of +Victoria Land and of Graham's Land, and reached the parallel of 80° S. +Sir James Ross was himself a naturalist of no mean acquirements, and Dr. +Hooker,[3] the present President of the Royal Society, accompanied him as +naturalist to the expedition, so that the observations upon the fauna and +flora of the Antarctic regions made during this cruise were sure to have +a peculiar value and importance, even had not the attention of the +voyagers been particularly directed to the importance of noting the +occurrence of the minutest forms of animal and vegetable life in the +ocean. + +[Footnote 3: Now Sir Joseph Hooker. 1894.] + +Among the scientific instructions for the voyage drawn up by a committee +of the Royal Society, however, there is a remarkable letter from Von +Humboldt to Lord Minto, then First Lord of the Admiralty, in which, among +other things, he dwells upon the significance of the researches into the +microscopic composition of rocks, and the discovery of the great share +which microscopic organisms take in the formation of the crust of the +earth at the present day, made by Ehrenberg in the years 1836-39. +Ehrenberg, in fact, had shown that the extensive beds of "rotten-stone" +or "Tripoli" which occur in various parts of the world, and notably at +Bilin in Bohemia, consisted of accumulations of the silicious cases and +skeletons of _Diatomaceoe_, sponges, and _Radiolaria_; he had proved that +similar deposits were being formed by _Diatomaceoe_, in the pools of the +Thiergarten in Berlin and elsewhere, and had pointed out that, if it were +commercially worth while, rotten-stone might be manufactured by a process +of diatom-culture. Observations conducted at Cuxhaven in 1839, had +revealed the existence, at the surface of the waters of the Baltic, of +living Diatoms and _Radiolaria_ of the same species as those which, in a +fossil state, constitute extensive rocks of tertiary age at Caltanisetta, +Zante, and Oran, on the shores of the Mediterranean. + +Moreover, in the fresh-water rotten-stone beds of Bilin, Ehrenberg had +traced out the metamorphosis, effected apparently by the action of +percolating water, of the primitively loose and friable deposit of +organized particles, in which the silex exists in the hydrated or soluble +condition. The silex, in fact, undergoes solution and slow redeposition, +until, in ultimate result, the excessively fine-grained sand, each +particle of which is a skeleton, becomes converted into a dense opaline +stone, with only here and there an indication of an organism. + +From the consideration of these facts, Ehrenberg, as early as the year +1839, had arrived at the conclusion that rocks, altogether similar to +those which constitute a large part of the crust of the earth, must be +forming, at the present day, at the bottom of the sea; and he threw out +the suggestion that even where no trace of organic structure is to be +found in the older rocks, it may have been lost by metamorphosis.[4] + +[Footnote 4: _Ueber die noch jetzt zahlreich lebende Thierarten der +Kreidebildung und den Organismus der Polythalamien. Abhandlungen der Kön. +Akad. der Wissenchaften._ 1839. _Berlin_. 1841. I am afraid that this +remarkable paper has been somewhat overlooked in the recent discussions +of the relation of ancient rocks to modern deposits.] + +The results of the Antarctic exploration, as stated by Dr. Hooker in the +"Botany of the Antarctic Voyage," and in a paper which he read before +the British Association in 1847, are of the greatest importance in +connection with these views, and they are so clearly stated in the former +work, which is somewhat inaccessible, that I make no apology for quoting +them at length-- + +"The waters and the ice of the South Polar Ocean were alike found to +abound with microscopic vegetables belonging to the order _Diatomaceoe_. +Though much too small to be discernible by the naked eye, they occurred +in such countless myriads as to stain the berg and the pack ice wherever +they were washed by the swell of the sea; and, when enclosed in the +congealing surface of the water, they imparted to the brash and pancake +ice a pale ochreous colour. In the open ocean, northward of the frozen +zone, this order, though no doubt almost universally present, generally +eludes the search of the naturalist; except when its species are +congregated amongst that mucous scum which is sometimes seen floating on +the waves, and of whose real nature we are ignorant; or when the coloured +contents of the marine animals who feed on these Algae are examined. To +the south, however, of the belt of ice which encircles the globe, between +the parallels of 50° and 70° S., and in the waters comprised between that +belt and the highest latitude ever attained by man, this vegetation is +very conspicuous, from the contrast between its colour and the white snow +and ice in which it is imbedded. Insomuch, that in the eightieth degree, +all the surface ice carried along by the currents, the sides of every +berg and the base of the great Victoria Barrier itself, within reach of +the swell, were tinged brown, as if the polar waters were charged with +oxide of iron. + +"As the majority of these plants consist of very simple vegetable cells, +enclosed in indestructible silex (as other Algae are in carbonate of +lime), it is obvious that the death and decomposition of such multitudes +must form sedimentary deposits, proportionate in their extent to the +length and exposure of the coast against which they are washed, in +thickness to the power of such agents as the winds, currents, and sea, +which sweep them more energetically to certain positions, and in purity, +to the depth of the water and nature of the bottom. Hence we detected +their remains along every icebound shore, in the depths of the adjacent +ocean, between 80 and 400 fathoms. Off Victoria Barrier (a perpendicular +wall of ice between one and two hundred feet above the level of the sea) +the bottom of the ocean was covered with a stratum of pure white or green +mud, composed principally of the silicious shells of the _Diatomaceoe_. +These, on being put into water, rendered it cloudy like milk, and took +many hours to subside. In the very deep water off Victoria and Graham's +Land, this mud was particularly pure and fine; but towards the shallow +shores there existed a greater or less admixture of disintegrated rock +and sand; so that the organic compounds of the bottom frequently bore but +a small proportion to the inorganic." ... + +"The universal existence of such an invisible vegetation as that of the +Antarctic Ocean, is a truly wonderful fact, and the more from its not +being accompanied by plants of a high order. During the years we spent +there, I had been accustomed to regard the phenomena of life as differing +totally from what obtains throughout all other latitudes, for everything +living appeared to be of animal origin. The ocean swarmed with +_Mollusca_, and particularly entomostracous _Crustacea_, small whales, +and porpoises; the sea abounded with penguins and seals, and the air with +birds; the animal kingdom was ever present, the larger creatures preying +on the smaller, and these again on smaller still; all seemed carnivorous. +The herbivorous were not recognised, because feeding on a microscopic +herbage, of whose true nature I had formed an erroneous impression. It +is, therefore, with no little satisfaction that I now class the +_Diatomaceoe_ with plants, probably maintaining in the South Polar Ocean +that balance between the vegetable and the animal kingdoms which prevails +over the surface of our globe. Nor is the sustenance and nutrition of the +animal kingdom the only function these minute productions may perform; +they may also be the purifiers of the vitiated atmosphere, and thus +execute in the Antarctic latitudes the office of our trees and grass turf +in the temperate regions, and the broad leaves of the palm, &c., in the +tropics." ... + +With respect to the distribution of the _Diatomaceoe_, Dr. Hooker +remarks:-- + +"There is probably no latitude between that of Spitzbergen and Victoria +Land, where some of the species of either country do not exist: Iceland, +Britain, the Mediterranean Sea, North and South America, and the South +Sea Islands, all possess Antarctic _Diatomaceoe_. The silicious coats of +species only known living in the waters of the South Polar Ocean, have, +during past ages, contributed to the formation of rocks; and thus they +outlive several successive creations of organized beings. The phonolite +stones of the Rhine, and the Tripoli stone, contain species identical +with what are now contributing to form a sedimentary deposit (and +perhaps, at some future period, a bed of rock) extending in one +continuous stratum for 400 measured miles. I allude to the shores of the +Victoria Barrier, along whose coast the soundings examined were +invariably charged with diatomaceous remains, constituting a bank which +stretches 200 miles north from the base of Victoria Barrier, while the +average depth of water above it is 300 fathoms, or 1,800 feet. Again, +some of the Antarctic species have been detected floating in the +atmosphere which overhangs the wide ocean between Africa and America. The +knowledge of this marvellous fact we owe to Mr. Darwin, who, when he was +at sea off the Cape de Verd Islands, collected an impalpable powder which +fell on Captain Fitzroy's ship. He transmitted this dust to Ehrenberg, +who ascertained it to consist of the silicious coats, chiefly of American +_Diatomaceoe_, which were being wafted through the upper region of the +air, when some meteorological phenomena checked them in their course and +deposited them on the ship and surface of the ocean. + +"The existence of the remains of many species of this order (and amongst +them some Antarctic ones) in the volcanic ashes, pumice, and scoriae of +active and extinct volcanoes (those of the Mediterranean Sea and +Ascension Island, for instance) is a fact bearing immediately upon the +present subject. Mount Erebus, a volcano 12,400 feet high, of the first +class in dimensions and energetic action, rises at once from the ocean in +the seventy-eighth degree of south latitude, and abreast of the +_Diatomaceoe_ bank, which reposes in part on its base. Hence it may not +appear preposterous to conclude that, as Vesuvius receives the waters of +the Mediterranean, with its fish, to eject them by its crater, so the +subterranean and subaqueous forces which maintain Mount Erebus in +activity may occasionally receive organic matter from the bank, and +disgorge it, together with those volcanic products, ashes and pumice. + +"Along the shores of Graham's Land and the South Shetland Islands, we +have a parallel combination of igneous and aqueous action, accompanied +with an equally copious supply of _Diatomaceoe_. In the Gulf of Erebus +and Terror, fifteen degrees north of Victoria Land, and placed on the +opposite side of the globe, the soundings were of a similar nature with +those of the Victoria Land and Barrier, and the sea and ice as full of +_Diatomaceoe_. This was not only proved by the deep sea lead, but by the +examination of bergs which, once stranded, had floated off and become +reversed, exposing an accumulation of white friable mud frozen to their +bases, which abounded with these vegetable remains." + +The _Challenger_ has explored the Antarctic seas in a region intermediate +between those examined by Sir James Ross's expedition; and the +observations made by Dr. Wyville Thomson and his colleagues in every +respect confirm those of Dr. Hooker:-- + +"On the 11th of February, lat. 60° 52' S., long. 80° 20' E., and March 3, +lat. 53° 55' S., long. 108° 35' E., the sounding instrument came up +filled with a very fine cream-coloured paste, which scarcely effervesced +with acid, and dried into a very light, impalpable, white powder. This, +when examined under the microscope, was found to consist almost entirely +of the frustules of Diatoms, some of them wonderfully perfect in all the +details of their ornament, and many of them broken up. The species of +Diatoms entering into this deposit have not yet been worked up, but they +appear to be referable chiefly to the genera _Fragillaria, Coscinodiscus, +Choetoceros, Asteromphalus_, and _Dictyocha_, with fragments of the +separated rods of a singular silicious organism, with which we were +unacquainted, and which made up a large proportion of the finer matter of +this deposit. Mixed with the Diatoms there were a few small +_Globigerinoe_, some of the tests and spicules of Radiolarians, and some +sand particles; but these foreign bodies were in too small proportion to +affect the formation as consisting practically of Diatoms alone. On the +4th of February, in lat. 52°, 29' S., long., 71° 36" E., a little to the +north of the Heard Islands, the tow-net, dragging a few fathoms below the +surface, came up nearly filled with a pale yellow gelatinous mass. This +was found to consist entirely of Diatoms of the same species as those +found at the bottom. By far the most abundant was the little bundle of +silicious rods, fastened together loosely at one end, separating from one +another at the other end, and the whole bundle loosely twisted into a +spindle. The rods are hollow, and contain the characteristic endochrome +of the _Diatomaceoe_. Like the _Globigerina_ ooze, then, which it +succeeds to the southward in a band apparently of no great width, the +materials of this silicious deposit are derived entirely from the surface +and intermediate depths. It is somewhat singular that Diatoms did not +appear to be in such large numbers on the surface over the Diatom ooze as +they were a little further north. This may perhaps be accounted for by +our not having struck their belt of depth with the tow-net; or it is +possible that when we found it on the 11th of February the bottom deposit +was really shifted a little to the south by the warm current, the +excessively fine flocculent _débris_ of the Diatoms taking a certain time +to sink. The belt of Diatom ooze is certainly a little further to the +southward in long. 83° E., in the path of the reflux of the Agulhas +current, than in long. 108° E. + +"All along the edge of the ice-pack--everywhere, in fact, to the south of +the two stations--on the 11th of February on our southward voyage, and on +the 3rd of March on our return, we brought up fine sand and grayish mud, +with small pebbles of quartz and felspar, and small fragments of mica- +slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, I +have no doubt, was derived from the surface like the others, but in this +case by the melting of icebergs and the precipitation of foreign matter +contained in the ice. + +"We never saw any trace of gravel or sand, or any material necessarily +derived from land, on an iceberg. Several showed vertical or irregular +fissures filled with discoloured ice or snow; but, when looked at +closely, the discoloration proved usually to be very slight, and the +effect at a distance was usually due to the foreign material filling the +fissure reflecting light less perfectly than the general surface of the +berg. I conceive that the upper surface of one of these great tabular +southern icebergs, including by far the greater part of its bulk, and +culminating in the portion exposed above the surface of the sea, was +formed by the piling up of successive layers of snow during the period, +amounting perhaps to several centuries, during which the ice-cap was +slowly forcing itself over the low land and out to sea over a long extent +of gentle slope, until it reached a depth considerably above 200 fathoms, +when the lower specific weight of the ice caused an upward strain which +at length overcame the cohesion of the mass, and portions were rent off +and floated away. If this be the true history of the formation of these +icebergs, the absence of all land _débris_ in the portion exposed above +the surface of the sea is readily understood. If any such exist, it must +be confined to the lower part of the berg, to that part which has at one +time or other moved on the floor of the ice-cap. + +"The icebergs, when they are first dispersed, float in from 200 to 250 +fathoms. When, therefore, they have been drifted to latitudes of 65° or +64° S., the bottom of the berg just reaches the layer at which the +temperature of the water is distinctly rising, and it is rapidly melted, +and the mud and pebbles with which it is more or less charged are +precipitated. That this precipitation takes place all over the area where +the icebergs are breaking up, constantly, and to a considerable extent, +is evident from the fact of the soundings being entirely composed of such +deposits; for the Diatoms, _Globigerinoe_, and radiolarians are present +on the surface in large numbers; and unless the deposit from the ice were +abundant it would soon be covered and masked by a layer of the exuvia of +surface organisms." + +The observations which have been detailed leave no doubt that the +Antarctic sea bottom, from a little to the south of the fiftieth +parallel, as far as 80° S., is being covered by a fine deposit of +silicious mud, more or less mixed, in some parts, with the ice-borne +_débris_ of polar lands and with the ejections of volcanoes. The +silicious particles which constitute this mud, are derived, in part, from +the diatomaceous plants and radiolarian animals which throng the surface, +and, in part, from the spicula of sponges which live at the bottom. The +evidence respecting the corresponding Arctic area is less complete, but +it is sufficient to justify the conclusion that an essentially similar +silicious cap is being formed around the northern pole. + +There is no doubt that the constituent particles of this mud may +agglomerate into a dense rock, such as that formed at Oran on the shores +of the Mediterranean, which is made up of similar materials. Moreover, in +the case of freshwater deposits of this kind it is certain that the +action of percolating water may convert the originally soft and friable, +fine-grained sandstone into a dense, semi-transparent opaline stone, the +silicious organized skeletons being dissolved, and the silex re-deposited +in an amorphous state. Whether such a metamorphosis as this occurs in +submarine deposits, as well as in those formed in fresh water, does not +appear; but there seems no reason to doubt that it may. And hence it may +not be hazardous to conclude that very ordinary metamorphic agencies may +convert these polar caps into a form of quartzite. + +In the great intermediate zone, occupying some 110° of latitude, which +separates the circumpolar Arctic and Antarctic areas of silicious +deposit, the Diatoms and _Radiolaria_ of the surface water and the +sponges of the bottom do not die out, and, so far as some forms are +concerned, do not even appear to diminish in total number; though, on a +rough estimate, it would appear that the proportion of _Radiolaria_ to +Diatoms is much greater than in the colder seas. Nevertheless the +composition of the deep-sea mud of this intermediate zone is entirely +different from that of the circumpolar regions. + +The first exact information respecting the nature of this mud at depths +greater than 1,000 fathoms was given by Ehrenberg, in the account which +he published in the "Monatsberichte" of the Berlin Academy for the year +1853, of the soundings obtained by Lieut. Berryman, of the United States +Navy, in the North Atlantic, between Newfoundland and the Azores. + +Observations which confirm those of Ehrenberg in all essential respects +have been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter, +and Professor Wyville Thomson, in their earlier cruises; and the +continuation of the _Globigerina_ ooze over the South Pacific has been +proved by the recent work of the _Challenger_, by which it is also shown, +for the first time, that, in passing from the equator to high southern +latitudes, the number and variety of the _Foraminifera_ diminishes, and +even the _Globigerinoe_ become dwarfed. And this result, it will be +observed, is in entire accordance with the fact already mentioned that, +in the sea of Kamschatka, the deep-sea mud was found by Bailey to contain +no calcareous organisms. + +Thus, in the whole of the "intermediate zone," the silicious deposit +which is being formed there, as elsewhere, by the accumulation of sponge- +spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by the +immensely greater amount of calcareous sediment, which arises from the +aggregation of the skeletons of dead _Foraminifera_. The similarity of +the deposit, thus composed of a large percentage of carbonate of lime, +and a small percentage of silex, to chalk, regarded merely as a kind of +rock, which was first pointed out by Ehrenberg,[5] is now admitted on all +hands; nor can it be reasonably doubted, that ordinary metamorphic +agencies are competent to convert the "modern chalk" into hard limestone +or even into crystalline marble. + +[Footnote 5: The following passages in Ehrenberg's memoir on _The +Organisms in the Chalk which are still living_ (1839), are conclusive:-- + +"7. The dawning period of the existing living organic creation, if such a +period is distinguishable (which is doubtful), can only be supposed to +have existed on the other side of, and below, the chalk formation; and +thus, either the chalk, with its widespread and thick beds, must enter +into the series of newer formations; or some of the accepted four great +geological periods, the quaternary, tertiary, and secondary formations, +contain organisms which still live. It is more probable, in the +proportion of 3 to 1, that the transition or primary period is not +different, but that it is only more difficult to examine and understand, +by reason of the gradual and prolonged chemical decomposition and +metamorphosis of many of its organic constituents." + +"10. By the mass-forming _Infasoria_ and _Polythalamia_, secondary are +not distinguishable from tertiary formations; and, from what has been +said, it is possible that, at this very day, rock masses are forming in +the sea, and being raised by volcanic agencies, the constitution of +which, on the whole, is altogether similar to that of the chalk. The +chalk remains distinguishable by its organic remains as a formation, but +not as a kind of rock."] + +Ehrenberg appears to have taken it for granted that the _Globigerinoe_ +and other _Foraminifera_ which are found in the deep-sea mud, live at the +great depths in which their remains are found; and he supports this +opinion by producing evidence that the soft parts of these organisms are +preserved, and may be demonstrated by removing the calcareous matter with +dilute acids. In 1857, the evidence for and against this conclusion +appeared to me to be insufficient to warrant a positive conclusion one +way or the other, and I expressed myself in my report to the Admiralty on +Captain Dayman's soundings in the following terms:-- + +"When we consider the immense area over which this deposit is spread, the +depth at which its formation is going on, and its similarity to chalk, +and still more to such rocks as the marls of Caltanisetta, the question, +whence are all these organisms derived? becomes one of high scientific +interest. + +"Three answers have suggested themselves:-- + +"In accordance with the prevalent view of the limitation of life to +comparatively small depths, it is imagined either: 1, that these +organisms have drifted into their present position from shallower waters; +or 2, that they habitually live at the surface of the ocean, and only +fall down into their present position. + +"1. I conceive that the first supposition is negatived by the extremely +marked zoological peculiarity of the deep-sea fauna. + +"Had the _Globigerinoe_ been drifted into their present position from +shallow water, we should find a very large proportion of the +characteristic inhabitants of shallow waters mixed with them, and this +would the more certainly be the case, as the large _Globigerinoe_, so +abundant in the deep-sea soundings, are, in proportion to their size, +more solid and massive than almost any other _Foraminifera_. But the fact +is that the proportion of other _Foraminifera_ is exceedingly small, nor +have I found as yet, in the deep-sea deposits, any such matters as +fragments of molluscous shells, of _Echini_, &c., which abound in shallow +waters, and are quite as likely to be drifted as the heavy +_Globigerinoe_. Again, the relative proportions of young and fully formed +_Globigerinoe_ seem inconsistent with the notion that they have travelled +far. And it seems difficult to imagine why, had the deposit been +accumulated in this way, _Coscinodisci_ should so almost entirely +represent the _Diatomaceoe_. + +"2. The second hypothesis is far more feasible, and is strongly supported +by the fact that many _Polycistineoe [Radiolaria]_ and _Coscinodisci_ are +well known to live at the surface of the ocean. Mr. Macdonald, Assistant- +Surgeon of H.M.S. _Herald_, now in the South-Western Pacific, has lately +sent home some very valuable observations on living forms of this kind, +met with in the stomachs of oceanic mollusks, and therefore certainly +inhabitants of the superficial layer of the ocean. But it is a singular +circumstance that only one of the forms figured by Mr. Macdonald is at +all like a _Globigerina_, and there are some peculiarities about even +this which make me greatly doubt its affinity with that genus. The form, +indeed, is not unlike that of a _Globigerina_, but it is provided with +long radiating processes, of which I have never seen any trace in +_Globigerina_. Did they exist, they might explain what otherwise is a +great objection to this view, viz., how is it conceivable that the heavy +_Globigerina_ should maintain itself at the surface of the water? + +"If the organic bodies in the deep-sea soundings have neither been +drifted, nor have fallen from above, there remains but one alternative-- +they must have lived and died where they are. + +"Important objections, however, at once suggest themselves to this view. +How can animal life be conceived to exist under such conditions of light, +temperature, pressure, and aeration as must obtain at these vast depths? + +"To this one can only reply that we know for a certainty that even very +highly-organized animals do continue to live at a depth of 300 and 400 +fathoms, inasmuch as they have been dredged up thence; and that the +difference in the amount of light and heat at 400 and at 2,000 fathoms is +probably, so to speak, very far less than the difference in complexity of +organisation between these animals and the humbler _Protozoa_ and +_Protophyta_ of the deep-sea soundings. + +"I confess, though as yet far from regarding it proved that the +_Globigerinoe_ live at these depths, the balance of probabilities seems +to me to incline in that direction. And there is one circumstance which +weighs strongly in my mind. It may be taken as a law that any genus of +animals which is found far back in time is capable of living under a +great variety of circumstances as regards light, temperature, and +pressure. Now, the genus _Globigerina_ is abundantly represented in the +cretaceous epoch, and perhaps earlier. + +"I abstain, however, at present from drawing any positive conclusions, +preferring rather to await the result of more extended observations."[6] + +[Footnote 6: Appendix to Report on Deep-sea Soundings in the Atlantic +Ocean, by Lieut.-Commander Joseph Dayman. 1857.] + +Dr. Wallich, Professor Wyville Thomson, and Dr. Carpenter concluded that +the _Globigerinoe_ live at the bottom. Dr. Wallich writes in 1862--"By +sinking very fine gauze nets to considerable depths, I have repeatedly +satisfied myself that _Globigerina_ does not occur in the superficial +strata of the ocean."[7] Moreover, having obtained certain living star- +fish from a depth of 1,260 fathoms, and found their stomachs full of +"fresh-looking _Globigerinoe_" and their _débris_--he adduces this fact +in support of his belief that the _Globigerinoe_ live at the bottom. + +[Footnote 7: The _North Atlantic Sea-bed_, p. 137.] + +On the other hand, Müller, Haeckel, Major Owen, Mr. Gwyn Jeffries, and +other observers, found that _Globigerinoe_, with the allied genera +_Orbulina_ and _Pulvinulina_, sometimes occur abundantly at the surface +of the sea, the shells of these pelagic forms being not unfrequently +provided with the long spines noticed by Macdonald; and in 1865 and 1866, +Major Owen more especially insisted on the importance of this fact. The +recent work of the _Challenger_ fully confirms Major Owen's statement. In +the paper recently published in the proceedings of the Royal Society,[8] +from which a quotation has already been made, Professor Wyville Thomson +says:-- + +"I had formed and expressed a very strong opinion on the matter. It +seemed to me that the evidence was conclusive that the _Foraminifera_ +which formed the _Globigerina_ ooze lived on the bottom, and that the +occurrence of individuals on the surface was accidental and exceptional; +but after going into the thing carefully, and considering the mass of +evidence which has been accumulated by Mr. Murray, I now admit that I was +in error; and I agree with him that it may be taken as proved that all +the materials of such deposits, with the exception, of course, of the +remains of animals which we now know to live at the bottom at all depths, +which occur in the deposit as foreign bodies, are derived from the +surface. + +[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procured +by the soundings of H.M.S. _Challenger_ during her cruise in the Southern +Seas, in the early part of the year 1874."--_Proceedings of the Royal +Society_, Nov. 26, 1874.] + +"Mr. Murray has combined with a careful examination of the soundings a +constant use of the tow-net, usually at the surface, but also at depths +of from ten to one hundred fathoms; and he finds the closest relation to +exist between the surface fauna of any particular locality and the +deposit which is taking place at the bottom. In all seas, from the +equator to the polar ice, the tow-net contains _Globigerinoe_. They are +more abundant and of a larger size in warmer seas; several varieties, +attaining a large size and presenting marked varietal characters, are +found in the intertropical area of the Atlantic. In the latitude of +Kerguelen they are less numerous and smaller, while further south they +are still more dwarfed, and only one variety, the typical _Globigerina +bulloides_, is represented. The living _Globigerinoe_ from the tow-net +are singularly different in appearance from the dead shells we find at +the bottom. The shell is clear and transparent, and each of the pores +which penetrate it is surrounded by a raised crest, the crest round +adjacent pores coalescing into a roughly hexagonal network, so that the +pores appear to lie at the bottom of a hexagonal pit. At each angle of +this hexagon the crest gives off a delicate flexible calcareous spine, +which is sometimes four or five times the diameter of the shell in +length. The spines radiate symmetrically from the direction of the centre +of each chamber of the shell, and the sheaves of long transparent needles +crossing one another in different directions have a very beautiful +effect. The smaller inner chambers of the shell are entirely filled with +an orange-yellow granular sarcode; and the large terminal chamber usually +contains only a small irregular mass, or two or three small masses run +together, of the same yellow sarcode stuck against one side, the +remainder of the chamber being empty. No definite arrangement and no +approach to structure was observed in the sarcode, and no +differentiation, with the exception of round bright-yellow oil-globules, +very much like those found in some of the radiolarians, which are +scattered, apparently irregularly, in the sarcode. We never have been +able to detect, in any of the large number of _Globigerinoe_ which we +have examined, the least trace of pseudopodia, or any extension, in any +form, of the sarcode beyond the shell. + + * * * * * + +"In specimens taken with the tow-net the spines are very usually absent; +but that is probably on account of their extreme tenuity; they are broken +off by the slightest touch. In fresh examples from the surface, the dots +indicating the origin of the lost spines may almost always be made out +with a high power. There are never spines on the _Globigerinoe_ from the +bottom, even in the shallowest water." + + +There can now be no doubt, therefore, that _Globigerinoe_ live at the top +of the sea; but the question may still be raised whether they do not also +live at the bottom. In favour of this view, it has been urged that the +shells of the _Globigerinoe_ of the surface never possess such thick +walls as those which are fouled at the bottom, but I confess that I doubt +the accuracy of this statement. Again, the occurrence of minute +_Globigerinoe_ in all stages of development, at the greatest depths, is +brought forward as evidence that they live _in situ_. But considering the +extent to which the surface organisms are devoured, without +discrimination of young and old, by _Salpoe_ and the like, it is not +wonderful that shells of all ages should be among the rejectamenta. Nor +can the presence of the soft parts of the body in the shells which form +the _Globigerina_ ooze, and the fact, if it be one, that animals living +at the bottom use them as food, be considered as conclusive evidence that +the _Globigerinoe_ live at the bottom. Such as die at the surface, and +even many of those which are swallowed by other animals, may retain much +of their protoplasmic matter when they reach the depths at which the +temperature sinks to 34° or 32° Fahrenheit, where decomposition must +become exceedingly slow. + +Another consideration appears to me to be in favour of the view that the +_Globigerinoe_ and their allies are essentially surface animals. This is +the fact brought out by the _Challenger's_ work, that they have a +southern limit of distribution, which can hardly depend upon anything but +the temperature of the surface water. And it is to be remarked that this +southern limit occurs at a lower latitude in the Antarctic seas than it +does in the North Atlantic. According to Dr. Wallich ("The North Atlantic +Sea Bed," p. 157) _Globigerina_ is the prevailing form in the deposits +between the Faroe Islands and Iceland, and between Iceland and East +Greenland--or, in other words, in a region of the sea-bottom which lies +altogether north of the parallel of 60° N.; while in the southern seas, +the _Globigerinoe_ become dwarfed and almost disappear between 50° and +55° S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_ +have vanished in 56° N., so that the persistence of the _Globigerina_ +ooze in high latitudes, in the North Atlantic, would seem to depend on +the northward curve of the isothermals peculiar to this region; and it is +difficult to understand how the formation of _Globigerina_ ooze can be +affected by this climatal peculiarity unless it be effected by surface +animals. + +Whatever may be the mode of life of the _Foraminifera_, to which the +calcareous element of the deep-sea "chalk" owes its existence, the fact +that it is the chief and most widely spread material of the sea-bottom in +the intermediate zone, throughout both the Atlantic and Pacific Oceans, +and the Indian Ocean, at depths from a few hundred to over two thousand +fathoms, is established. But it is not the only extensive deposit which +is now taking place. In 1853, Count Pourtalès, an officer of the United +States Coast Survey, which has done so much for scientific hydrography, +observed, that the mud forming the sea-bottom at depths of one hundred +and fifty fathoms, in 31° 32' N., 79° 35' W., off the Coast of Florida, +was "a mixture, in about equal proportions, of _Globigerinoe_ and black +sand, probably greensand, as it makes a green mark when crushed on +paper." Professor Bailey, examining these grains microscopically, found +that they were casts of the interior cavities of _Foraminifera_, +consisting of a mineral known as _Glauconite_, which is a silicate of +iron and alumina. In these casts the minutest cavities and finest tubes +in the Foraminifer were sornetilnes reproduced in solid counterparts of +the glassy mineral, while the calcareous original had been entirely +dissolved away. + +Contemporaneously with these observations, the indefatigable Ehrenberg +had discovered that the "greensands" of the geologist were largely made +up of casts of a similar character, and proved the existence of +_Foraminifera_ at a very ancient geological epoch, by discovering such +casts in a greensand of Lower Silurian age, which occurs near St. +Petersburg. + +Subsequently, Messrs. Parker and Jones discovered similar casts in +process of formation, the original shell not having disappeared, in +specimens of the sea-bottom of the Australian seas, brought home by the +late Professor Jukes. And the _Challenger_ has observed a deposit of a +similar character in the course of the Agulhas current, near the Cape of +Good Hope, and in some other localities not yet defined. + +It would appear that this infiltration of _Foraminifera_ shells with +_Glauconite_ does not take place at great depths, but rather in what may +be termed a sublittoral region, ranging from a hundred to three hundred +fathoms. It cannot be ascribed to any local cause, for it takes place, +not only over large areas in the Gulf of Mexico and the Coast of Florida, +but in the South Atlantic and in the Pacific. But what are the conditions +which determine its occurrence, and whence the silex, the iron, and the +alumina (with perhaps potash and some other ingredients in small +quantity) of which the _Glauconite_ is composed, proceed, is a point on +which no light has yet been thrown. For the present we must be content +with the fact that, in certain areas of the "intermediate zone," +greensand is replacing and representing the primitively calcareo- +silicious ooze. + +The investigation of the deposits which are now being formed in the basin +of the Mediterranean, by the late Professor Edward Forbes, by Professor +Williamson and more recently by Dr. Carpenter, and a comparison of the +results thus obtained with what is known of the surface fauna, have +brought to light the remarkable fact, that while the surface and the +shallows abound with _Foraminifera_ and other calcareous shelled +organisms, the indications of life become scanty at depths beyond 500 or +600 fathoms, while almost all traces of it disappear at greater depths, +and at 1,000 to 2,000 fathoms the bottom is covered with a fine clay. + +Dr. Carpenter has discussed the significance of this remarkable fact, and +he is disposed to attribute the absence of life at great depths, partly +to the absence of any circulation of the water of the Mediterranean at +such depths, and partly to the exhaustion of the oxygen of the water by +the organic matter contained in the fine clay, which he conceives to be +formed by the finest particles of the mud brought down by the rivers +which flow into the Mediterranean. + +However this may be, the explanation thus offered of the presence of the +fine mud, and of the absence of organisms which ordinarily live at the +bottom, does not account for the absence of the skeletons of the +organisms which undoubtedly abound at the surface of the Mediterranean; +and it would seem to have no application to the remarkable fact +discovered by the _Challenger_, that in the open Atlantic and Pacific +Oceans, in the midst of the great intermediate zone, and thousands of +miles away from the embouchure of any river, the sea-bottom, at depths +approaching to and beyond 3,000 fathoms, no longer consists of +_Globigerina_ ooze, but of an excessively fine red clay. + +Professor Thomson gives the following account of this capital +discovery:-- + +"According to our present experience, the deposit of _Globigerina_ ooze +is limited to water of a certain depth, the extreme limit of the pure +characteristic formation being placed at a depth of somewhere about 2,250 +fathoms. Crossing from these shallower regions occupied by the ooze into +deeper soundings, we find, universally, that the calcareous formation +gradually passes into, and is finally replaced by, an extremely fine pure +clay, which occupies, speaking generally, all depths below 2,500 fathoms, +and consists almost entirely of a silicate of the red oxide of iron and +alumina. The transition is very slow, and extends over several hundred +fathoms of increasing depth; the shells gradually lose their sharpness of +outline, and assume a kind of 'rotten' look and a brownish colour, and +become more and more mixed with a fine amorphous red-brown powder, which +increases steadily in proportion until the lime has almost entirely +disappeared. This brown matter is in the finest possible state of +subdivision, so fine that when, after sifting it to separate any +organisms it might contain, we put it into jars to settle, it remained +for days in suspension, giving the water very much the appearance and +colour of chocolate. + +"In indicating the nature of the bottom on the charts, we came, from +experience and without any theoretical considerations, to use three terms +for soundings in deep water. Two of these, Gl. oz. and r. cl., were very +definite, and indicated strongly-marked formations, with apparently but +few characters in common; but we frequently got soundings which we could +not exactly call '_Globigerina_ ooze' or 'red clay,' and before we were +fully aware of the nature of these, we were in the habit of indicating +them as 'grey ooze' (gr. oz.) We now recognise the 'grey ooze' as an +intermediate stage between the _Globigerina_ ooze and the red clay; we +find that on one side, as it were, of an ideal line, the red clay +contains more and more of the material of the calcareous ooze, while on +the other, the ooze is mixed with an increasing proportion of 'red clay.' + +"Although we have met with the same phenomenon so frequently, that we +were at length able to predict the nature of the bottom from the depth of +the soundings with absolute certainty for the Atlantic and the Southern +Sea, we had, perhaps, the best opportunity of observing it in our first +section across the Atlantic, between Teneriffe and St. Thomas. The first +four stations on this section, at depths from 1,525 to 2,220 fathoms, +show _Globigerina_ ooze. From the last of these, which is about 300 miles +from Teneriffe, the depth gradually increases to 2,740 fathoms at 500, +and 2,950 fathoms at 750 miles from Teneriffe. The bottom in these two +soundings might have been called 'grey ooze,' for although its nature has +altered entirely from the _Globigerina_ ooze, the red clay into which it +is rapidly passing still contains a considerable admixture of carbonate +of lime. + +"The depth goes on increasing to a distance of 1,150 miles from +Teneriffe, when it reaches 3,150 fathoms; there the clay is pure and +smooth, and contains scarcely a trace of lime. From this great depth the +bottom gradually rises, and, with decreasing depth, the grey colour and +the calcareous composition of the ooze return. Three soundings in 2,050, +1,900, and 1,950 fathoms on the 'Dolphin Rise' gave highly characteristic +examples of the _Globigerina_ formation. Passing from the middle plateau +of the Atlantic into the western trough, with depths a little over 3,000 +fathoms, the red clay returned in all its purity; and our last sounding, +in 1,420 fathoms, before reaching Sombrero, restored the _Globigerina_ +ooze with its peculiar associated fauna. + +"This section shows also the wide extension and the vast geological +importance of the red clay formation. The total distance from Teneriffe +to Sombrero is about 2,700 miles. Proceeding from east to west, we have-- + +About 80 miles of volcanic mud and sand, + " 350 " _Globigerina_ ooze, + " 1,050 " red clay, + " 330 " _Globigerina_ ooze, + " 850 " red clay, + " 40 " _Globigerina_ ooze; + +giving a total of 1,900 miles of red clay to 720 miles of _Globigerina_ +ooze. + +"The nature and origin of this vast deposit of clay is a question of the +very greatest interest; and although I think there can be no doubt that +it is in the main solved, yet some matters of detail are still involved +in difficulty. My first impression was that it might be the most minutely +divided material, the ultimate sediment produced by the disintegration of +the land, by rivers and by the action of the sea on exposed coasts, and +held in suspension and distributed by ocean currents, and only making +itself manifest in places unoccupied by the _Globigerina_ ooze. Several +circumstances seemed, however, to negative this mode of origin. The +formation seemed too uniform: wherever we met with it, it had the same +character, and it only varied in composition in containing less or more +carbonate of lime. + +"Again, the were gradually becoming more and more convinced that all the +important elements of the _Globigerina_ ooze lived on the surface, and it +seemed evident that, so long as the condition on the surface remained the +same, no alteration of contour at the bottom could possibly prevent its +accumulation; and the surface conditions in the Mid-Atlantic were very +uniform, a moderate current of a very equal temperature passing +continuously over elevations and depressions, and everywhere yielding to +the tow-net the ooze-forming _Foraminifera_ in the same proportion. The +Mid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, the +shells of these are constantly mixed with the _Globigerina_ ooze, +sometimes in number sufficient to make up a considerable portion of its +bulk. It is clear that these shells must fall in equal numbers upon the +red clay, but scarcely a trace of one of them is ever brought up by the +dredge on the red clay area. It might be possible to explain the absence +of shell-secreting animals living on the bottom, on the supposition that +the nature of the deposit was injurious to them; but then the idea of a +current sufficiently strong to sweep them away is negatived by the +extreme fineness of the sediment which is being laid down; the absence of +surface shells appears to be intelligible only on the supposition that +they are in some way removed. + +"We conclude, therefore, that the 'red clay' is not an additional +substance introduced from without, and occupying certain depressed +regions on account of some law regulating its deposition, but that it is +produced by the removal, by some means or other, over these areas, of the +carbonate of lime, which forms probably about 98 per cent. of the +material of the _Globigerina_ ooze. We can trace, indeed, every +successive stage in the removal of the carbonate of lime in descending +the slope of the ridge or plateau where the _Globigerina_ ooze is +forming, to the region of the clay. We find, first, that the shells of +pteropods and other surface _Mollusca_ which are constantly falling on +the bottom, are absent, or, if a few remain, they are brittle and yellow, +and evidently decaying rapidly. These shells of _Mollusca_ decompose more +easily and disappear sooner than the smaller, and apparently more +delicate, shells of rhizopods. The smaller _Foraminifera_ now give way, +and are found in lessening proportion to the larger; the coccoliths first +lose their thin outer border and then disappear; and the clubs of the +rhabdoliths get worn out of shape, and are last seen, under a high power, +as infinitely minute cylinders scattered over the field. The larger +_Foraminifera_ are attacked, and instead of being vividly white and +delicately sculptured, they become brown and worn, and finally they break +up, each according to its fashion; the chamber-walls of _Globigerina_ +fall into wedge-shaped pieces, which quickly disappear, and a thick rough +crust breaks away from the surface of _Orbulina_, leaving a thin inner +sphere, at first beautifully transparent, but soon becoming opaque and +crumbling away. + +"In the meantime the proportion of the amorphous 'red clay' to the +calcareous elements of all kinds increases, until the latter disappear, +with the exception of a few scattered shells of the larger +_Foraminifera_, which are still found even in the most characteristic +samples of the 'red clay.' + +"There seems to be no room left for doubt that the red clay is +essentially the insoluble residue, the _ash_, as it were, of the +calcareous organisms which form the _Globigerina_ ooze, after the +calcareous matter has been by some means removed. An ordinary mixture of +calcareous _Foraminifera_ with the shells of pteropods, forming a fair +sample of _Globigerina_ ooze from near St. Thomas, was carefully washed, +and subjected by Mr. Buchanan to the action of weak acid; and he found +that there remained after the carbonate of lime had been removed, about 1 +per cent. of a reddish mud, consisting of silica, alumina, and the red +oxide of iron. This experiment has been frequently repeated with +different samples of _Globigerina_ ooze, and always with the result that +a small proportion of a red sediment remains, which possesses all the +characters of the red clay." + + * * * * * + +"It seems evident from the observations here recorded, that _clay_, which +we have hitherto looked upon as essentially the product of the +disintegration of older rocks, may be, under certain circumstances, an +organic formation like chalk; that, as a matter of fact, an area on the +surface of the globe, which we have shown to be of vast extent, although +we are still far from having ascertained its limits, is being covered by +such a deposit at the present day. + +"It is impossible to avoid associating such a formation with the fine, +smooth, homogeneous clays and schists, poor in fossils, but showing worm- +tubes and tracks, and bunches of doubtful branching things, such as +Oldhamia, silicious sponges, and thin-shelled peculiar shrimps. Such +formations, more or less metamorphosed, are very familiar, especially to +the student of palaeozoic geology, and they often attain a vast thickness. +One is inclined, from the great resemblance between them in composition +and in the general character of the included fauna, to suspect that these +may be organic formations, like the modern red clay of the Atlantic and +Southern Sea, accumulations of the insoluble ashes of shelled creatures. + +"The dredging in the red clay on the 13th of March was usually rich. The +bag contained examples, those with calcareous shells rather stunted, of +most of the characteristic deep-water groups of the Southern Sea, +including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha, +Pourtalesia_, and one or two _Mollusca_. This is, however, very rarely +the case. Generally the red clay is barren, or contains only a very small +number of forms." + +It must be admitted that it is very difficult, at present, to frame any +satisfactory explanation of the mode of origin of this singular deposit +of red clay. + +I cannot say that the theory put forward tentatively, and with much +reservation by Professor Thomson, that the calcareous matter is dissolved +out by the relatively fresh water of the deep currents from the Antarctic +regions, appears satisfactory to me. Nor do I see my way to the +acceptance of the suggestion of Dr. Carpenter, that the red clay is the +result of the decomposition of previously-formed greensand. At present +there is no evidence that greensand casts are ever formed at great +depths; nor has it been proved that _Glauconite_ is decomposable by the +agency of water and carbonic acid. + +I think it probable that we shall have to wait some time for a sufficient +explanation of the origin of the abyssal red clay, no less than for that +of the sublittoral greensand in the intermediate zone. But the importance +of the establishment of the fact that these various deposits are being +formed in the ocean, at the present day, remains the same; whether its +_rationale_ be understood or not. + +For, suppose the globe to be evenly covered with sea, to a depth say of a +thousand fathoms--then, whatever might be the mineral matter composing +the sea-bottom, little or no deposit would be formed upon it, the +abrading and denuding action of water, at such a depth, being exceedingly +slight. + +Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceous +plants, such as those which now exist in the deep-sea, to be introduced: +they would be distributed according to the same laws as at present, the +sponges (and possibly some of the _Foraminifera_), covering the bottom, +while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, would +increase and multiply in the surface waters. In accordance with the +existing state of things, the _Radiolaria_ and Diatoms would have a +universal distribution, the latter gathering most thickly in the polar +regions, while the _Foraminifera_ would be largely, if not exclusively, +confined to the intermediate zone; and, as a consequence of this +distribution, a bed of "chalk" would begin to form in the intermediate +zone, while caps of silicious rock would accumulate on the circumpolar +regions. + +Suppose, further, that a part of the intermediate area were raised to +within two or three hundred fathoms of the surface--for anything that we +know to the contrary, the change of level might determine the +substitution of greensand for the "chalk"; while, on the other hand, if +part of the same area were depressed to three thousand fathoms, that +change might determine the substitution of a different silicate of +alumina and iron--namely, clay--for the "chalk" that would otherwise be +formed. + +If the _Challenger_ hypothesis, that the red clay is the residue left by +dissolved _Foraminiferous_ skeletons, is correct, then all these deposits +alike would be directly, or indirectly, the product of living organisms. +But just as a silicious deposit may be metamorphosed into opal or +quartzite, and chalk into marble, so known metamorphic agencies may +metamorphose clay into schist, clay-slate, slate, gneiss, or even +granite. And thus, by the agency of the lowest and simplest of organisms, +our imaginary globe might be covered with strata, of all the chief kinds +of rock of which the known crust of the earth is composed, of indefinite +thickness and extent. + +The bearing of the conclusions which are now either established, or +highly probable, respecting the origin of silicious, calcareous, and +clayey rocks, and their metamorphic derivatives, upon the archaeology of +the earth, the elucidation of which is the ultimate object of the +geologist, is of no small importance. + +A hundred years ago the singular insight of Linnaeus enabled him to say +that "fossils are not the children but the parents of rocks,"[9] and the +whole effect of the discoveries made since his time has been to compile a +larger and larger commentary upon this text. It is, at present, a +perfectly tenable hypothesis that all siliceous and calcareous rocks are +either directly, or indirectly, derived from material which has, at one +time or other, formed part of the organized framework of living +organisms. Whether the same generalization may be extended to aluminous +rocks, depends upon the conclusion to be drawn from the facts respecting +the red clay areas brought to light by the _Challenger_. If we accept the +view taken by Wyville Thomson and his colleagues--that the red clay is +the residuum left after the calcareous matter of the _Globigerinoe_ ooze +has been dissolved away--then clay is as much a product of life as +limestone, and all known derivatives of clay may have formed part of +animal bodies. + +[Footnote 9: "Petrificata montium calcariorum non filii sed parentes +sunt, cum omnis calx oriatur ab animalibus."--_Systema Naturae_, Ed. xii., +t. iii., p. 154. It must be recollected that Linnaeus included silex, as +well as limestone, under the name of "calx," and that he would probably +have arranged Diatoms among animals, as part of "chaos." Ehrenberg quotes +another even more pithy passage, which I have not been able to find in +any edition of the _Systema_ accessible to me: "Sic lapides ab +animalibus, nec vice versa. Sic runes saxei non primaevi, sed temporis +filiae."] + +So long as the _Globigerinoe_;, actually collected at the surface, have +not been demonstrated to contain the elements of clay, the _Challenger_ +hypothesis, as I may term it, must be accepted with reserve and +provisionally, but, at present, I cannot but think that it is more +probable than any other suggestion which has been made. + +Accepting it provisionally, we arrive at the remarkable result that all +the chief known constituents of the crust of the earth may have formed +part of living bodies; that they may be the "ash" of protoplasm; that the +"_rupes saxei_" are not only _"temporis,"_ but "_vitae filiae_"; and, +consequently, that the time during which life has been active on the +globe may be indefinitely greater than the period, the commencement of +which is marked by the oldest known rocks, whether fossiliferous or +unfossiliferous. + +And thus we are led to see where the solution of a great problem and +apparent paradox of geology may lie. Satisfactory evidence now exists +that some animals in the existing world have been derived by a process of +gradual modification from pre-existing forms. It is undeniable, for +example, that the evidence in favour of the derivation of the horse from +the later tertiary _Hipparion_, and that of the _Hipparion_ from +_Anchitherium_, is as complete and cogent as such evidence can reasonably +be expected to be; and the further investigations into the history of the +tertiary mammalia are pushed, the greater is the accumulation of evidence +having the same tendency. So far from palaeontology lending no support to +the doctrine of evolution--as one sees constantly asserted--that +doctrine, if it had no other support, would have been irresistibly forced +upon us by the palaeontological discoveries of the last twenty years. + +If, however, the diverse forms of life which now exist have been produced +by the modification of previously-existing less divergent forms, the +recent and extinct species, taken as a whole, must fall into series which +must converge as we go back in time. Hence, if the period represented by +the rocks is greater than, or co-extensive with, that during which life +has existed, we ought, somewhere among the ancient formations, to arrive +at the point to which all these series converge, or from which, in other +words, they have diverged--the primitive undifferentiated protoplasmic +living things, whence the two great series of plants and animals have +taken their departure. + +But, as a matter of fact, the amount of convergence of series, in +relation to the time occupied by the deposition of geological formations, +is extraordinarily small. Of all animals the higher _Vertebrata_ are the +most complex; and among these the carnivores and hoofed animals +(_Ungulata_) are highly differentiated. Nevertheless, although the +different lines of modification of the _Carnivora_ and those of the +_Ungulata_, respectively, approach one another, and, although each group +is represented by less differentiated forms in the older tertiary rocks +than at the present day, the oldest tertiary rocks do not bring us near +the primitive form of either. If, in the same way, the convergence of the +varied forms of reptiles is measured against the time during which their +remains are preserved--which is represented by the whole of the tertiary +and mesozoic formations--the amount of that convergence is far smaller +than that of the lines of mammals between the present time and the +beginning of the tertiary epoch. And it is a broad fact that, the lower +we go in the scale of organization, the fewer signs are there of +convergence towards the primitive form from whence all must have +diverged, if evolution be a fact. Nevertheless, that it is a fact in some +cases, is proved, and I, for one, have not the courage to suppose that +the mode in which some species have taken their origin is different from +that in which the rest have originated. + +What, then, has become of all the marine animals which, on the hypothesis +of evolution, must have existed in myriads in those seas, wherein the +many thousand feet of Cambrian and Laurentian rocks now devoid, or almost +devoid, of any trace of life were deposited? + +Sir Charles Lyell long ago suggested that the azoic character of these +ancient formations might be due to the fact that they had undergone +extensive metamorphosis; and readers of the "Principles of Geology" will +be familiar with the ingenious manner in which he contrasts the theory of +the Gnome, who is acquainted only with the interior of the earth, with +those of ordinary philosophers, who know only its exterior. + +The metamorphism contemplated by the great modern champion of rational +geology is, mainly, that brought about by the exposure of rocks to +subterranean heat; and where no such heat could be shown to have +operated, his opponents assumed that no metamorphosis could have taken +place. But the formation of greensand, and still more that of the "red +clay" (if the _Challenger_ hypothesis be correct) affords an insight into +a new kind of metamorphosis--not igneous, but aqueous--by which the +primitive nature of a deposit may be masked as completely as it can be by +the agency of heat. And, as Wyville Thomson suggests, in the passage I +have quoted above (p. 17), it further enables us to assign a new cause +for the occurrence, so puzzling hitherto, of thousands of feet of +unfossiliferous fine-grained schists and slates, in the midst of +formations deposited in seas which certainly abounded in life. If the +great deposit of "red clay" now forming in the eastern valley of the +Atlantic were metamorphosed into slate and then upheaved, it would +constitute an "azoic" rock of enormous extent. And yet that rock is now +forming in the midst of a sea which swarms with living beings, the great +majority of which are provided with calcareous or silicious shells and +skeletons; and, therefore, are such as, up to this time, we should have +termed eminently preservable. + +Thus the discoveries made by the _Challenger_ expedition, like all recent +advances in our knowledge of the phenomena of biology, or of the changes +now being effected in the structure of the surface of the earth, are in +accordance with and lend strong support to, that doctrine of +Uniformitarianism, which, fifty years ago, was held only by a small +minority of English geologists--Lyell, Scrope, and De la Beche--but now, +thanks to the long-continued labours of the first two, and mainly to +those of Sir Charles Lyell, has gradually passed from the position of a +heresy to that of catholic doctrine. + +Applied within the limits of the time registered by the known fraction of +the crust of the earth, I believe that uniformitarianism is unassailable. +The evidence that, in the enormous lapse of time between the deposition +of the lowest Laurentian strata and the present day, the forces which +have modified the surface of the crust of the earth were different in +kind, or greater in the intensity of their action, than those which are +now occupied in the same work, has yet to be produced. Such evidence as +we possess all tends in the contrary direction, and is in favour of the +same slow and gradual changes occurring then as now. + +But this conclusion in nowise conflicts with the deductions of the +physicist from his no less clear and certain data. It may be certain that +this globe has cooled down from a condition in which life could not have +existed; it may be certain that, in so cooling, its contracting crust +must have undergone sudden convulsions, which were to our earthquakes as +an earthquake is to the vibration caused by the periodical eruption of a +Geyser; but in that case, the earth must, like other respectable parents, +have sowed her wild oats, and got through her turbulent youth, before we, +her children, have any knowledge of her. + +So far as the evidence afforded by the superficial crust of the earth +goes, the modern geologist can, _ex animo_, repeat the saying of Hutton, +"We find no vestige of a beginning--no prospect of an end." However, he +will add, with Hutton, "But in thus tracing back the natural operations +which have succeeded each other, and mark to us the course of time past, +we come to a period in which we cannot see any further." And if he seek +to peer into the darkness of this period, he will welcome the light +proffered by physics and mathematics. + + + +IV + + +YEAST + +[1871] + +It has been known, from time immemorial, that the sweet liquids which may +be obtained by expressing the juices of the fruits and stems of various +plants, or by steeping malted barley in hot water, or by mixing honey +with water--are liable to undergo a series of very singular changes, if +freely exposed to the air and left to themselves, in warm weather. +However clear and pellucid the liquid may have been when first prepared, +however carefully it may have been freed, by straining and filtration, +from even the finest visible impurities, it will not remain clear. After +a time it will become cloudy and turbid; little bubbles will be seen +rising to the surface, and their abundance will increase until the liquid +hisses as if it were simmering on the fire. By degrees, some of the solid +particles which produce the turbidity of the liquid collect at its +surface into a scum, which is blown up by the emerging air-bubbles into a +thick, foamy froth. Another moiety sinks to the bottom, and accumulates +as a muddy sediment, or "lees." + +When this action has continued, with more or less violence, for a certain +time, it gradually moderates. The evolution of bubbles slackens, and +finally comes to an end; scum and lees alike settle at the bottom, and +the fluid is once more clear and transparent. But it has acquired +properties of which no trace existed in the original liquid. Instead of +being a mere sweet fluid, mainly composed of sugar and water, the sugar +has more or less completely disappeared; and it has acquired that +peculiar smell and taste which we call "spirituous." Instead of being +devoid of any obvious effect upon the animal economy, it has become +possessed of a very wonderful influence on the nervous system; so that in +small doses it exhilarates, while in larger it stupefies, and may even +destroy life. + +Moreover, if the original fluid is put into a still, and heated +moderately, the first and last product of its distillation is simple +water; while, when the altered fluid is subjected to the same process, +the matter which is first condensed in the receiver is found to be a +clear, volatile substance, which is lighter than water, has a pungent +taste and smell, possesses the intoxicating powers of the fluid in an +eminent degree, and takes fire the moment it is brought in contact with a +flame. The Alchemists called this volatile liquid, which they obtained +from wine, "spirits of wine," just as they called hydrochloric acid +"spirits of salt," and as we, to this day, call refined turpentine +"spirits of turpentine." As the "spiritus," or breath, of a man was +thought to be the most refined and subtle part of him, the intelligent +essence of man was also conceived as a sort of breath, or spirit; and, by +analogy, the most refined essence of anything was called its "spirit." +And thus it has come about that we use the same word for the soul of man +and for a glass of gin. + +At the present day, however, we even more commonly use another name for +this peculiar liquid--namely, "alcohol," and its origin is not less +singular. The Dutch physician, Van Helmont, lived in the latter part of +the sixteenth and the beginning of the seventeenth century--in the +transition period between alchemy and chemistry--and was rather more +alchemist than chemist. Appended to his "Opera Omnia," published in 1707, +there is a very needful "Clavis ad obscuriorum sensum referendum," in +which the following passage occurs.-- + +"ALCOHOL.--Chymicis est liquor aut pulvis summé subtilisatus, vocabulo +Orientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_ +speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat +... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorum +cancri summé subtilisatus _alcohol_ audit, haud aliter ac spiritus +rectificatissimi _alcolisati_ dicuntur." + +Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, so +late as the middle of the last century, the English lexicographer, Nathan +Bailey, defines "alcohol" as "the pure substance of anything separated +from the more gross, a very fine and impalpable powder, or a very pure, +well-rectified spirit." But, by the time of the publication of +Lavoisier's "Traité Elémentaire de Chimie," in 1789, the term "alcohol," +"alkohol," or "alkool" (for it is spelt in all three ways), which Van +Helmont had applied primarily to a fine powder, and only secondarily to +spirits of wine, had lost its primary meaning altogether; and, from the +end of the last century until now, it has, I believe, been used +exclusively as the denotation of spirits of wine, and bodies chemically +allied to that substance. + +The process which gives rise to alcohol in a saccharine fluid is known +tones as "fermentation"; a term based upon the apparent boiling up or +"effervescence" of the fermenting liquid, and of Latin origin. + +Our Teutonic cousins call the same process "gähren," "gäsen," "göschen," +and "gischen"; but, oddly enough, we do not seem to have retained their +verb or their substantive denoting the action itself, though we do use +names identical with, or plainly derived from, theirs for the scum and +lees. These are called, in Low German, "gäscht" and "gischt"; in Anglo- +Saxon, "gest," "gist," and "yst," whence our "yeast." Again, in Low +German and in Anglo-Saxon there is another name for yeast, having the +form "barm," or "beorm"; and, in the Midland Counties, "barm" is the name +by which yeast is still best known. In High German, there is a third name +for yeast, "hefe," which is not represented in English, so far as I know. + +All these words are said by philologers to be derived from roots +expressive of the intestine motion of a fermenting substance. Thus "hefe" +is derived from "heben," to raise; "barm" from "beren" or "bären," to +bear up; "yeast," "yst," and "gist," have all to do with seething and +foam, with "yeasty" waves, and "gusty" breezes. + +The same reference to the swelling up of the fermenting substance is seen +in the Gallo-Latin terms "levure" and "leaven." + +It is highly creditable to the ingenuity of our ancestors that the +peculiar property of fermented liquids, in virtue of which they "make +glad the heart of man," seems to have been known in the remotest periods +of which we have any record. All savages take to alcoholic fluids as if +they were to the manner born. Our Vedic forefathers intoxicated +themselves with the juice of the "soma"; Noah, by a not unnatural +reaction against a superfluity of water, appears to have taken the +earliest practicable opportunity of qualifying that which he was obliged +to drink; and the ghosts of the ancient Egyptians were solaced by +pictures of banquets in which the wine-cup passes round, graven on the +walls of their tombs. A knowledge of the process of fermentation, +therefore, was in all probability possessed by the prehistoric +populations of the globe; and it must have become a matter of great +interest even to primaeval wine-bibbers to study the methods by which +fermented liquids could be surely manufactured. No doubt it was soon +discovered that the most certain, as well as the most expeditious, way of +making a sweet juice ferment was to add to it a little of the scum, or +lees, of another fermenting juice. And it can hardly be questioned that +this singular excitation of fermentation in one fluid, by a sort of +infection, or inoculation, of a little ferment taken from some other +fluid, together with the strange swelling, foaming, and hissing of the +fermented substance, must have always attracted attention from the more +thoughtful. Nevertheless, the commencement of the scientific analysis of +the phenomena dates from a period not earlier than the first half of the +seventeenth century. + +At this time, Van Helmont made a first step, by pointing out that the +peculiar hissing and bubbling of a fermented liquid is due, not to the +evolution of common air (which he, as the inventor of the term "gas," +calls "gas ventosum"), but to that of a peculiar kind of air such as is +occasionally met with in caves, mines, and wells, and which he calls "gas +sylvestre." + +But a century elapsed before the nature of this "gas sylvestre," or, as +it was afterwards called, "fixed air," was clearly determined, and it was +found to be identical with that deadly "choke-damp" by which the lives of +those who descend into old wells, or mines, or brewers' vats, are +sometimes suddenly ended; and with the poisonous aëriform fluid which is +produced by the combustion of charcoal, and now goes by the name of +carbonic acid gas. + +During the same time it gradually became evident that the presence of +sugar was essential to the production of alcohol and the evolution of +carbonic acid gas, which are the two great and conspicuous products of +fermentation. And finally, in 1787, the Italian chemist, Fabroni, made +the capital discovery that the yeast ferment, the presence of which is +necessary to fermentation, is what he termed a "vegeto-animal" substance; +that is, a body which gives of ammoniacal salts when it is burned, and +is, in other ways, similar to the gluten of plants and the albumen and +casein of animals. + +These discoveries prepared the way for the illustrious Frenchman, +Lavoisier, who first approached the problem of fermentation with a +complete conception of the nature of the work to be done. The words in +which he expresses this conception, in the treatise on elementary +chemistry to which reference has already been made, mark the year 1789 as +the commencement of a revolution of not less moment in the world of +science than that which simultaneously burst over the political world, +and soon engulfed Lavoisier himself in one of its mad eddies. + +"We may lay it down as an incontestable axiom that, in all the operations +of art and nature, nothing is created; an equal quantity of matter exists +both before, and after the experiment: the quality and quantity of the +elements remain precisely the same, and nothing takes place beyond +changes and modifications in the combinations of these elements. Upon +this principle the whole art of performing chemical experiments depends; +we must always suppose an exact equality between the elements of the body +examined and those of the products of its analysis. + +"Hence, since from must of grapes we procure alcohol and carbonic acid, I +have an undoubted right to suppose that must consists of carbonic acid +and alcohol. From these premisses we have two modes of ascertaining what +passes during vinous fermentation: either by determining the nature of, +and the elements which compose, the fermentable substances; or by +accurately examining the products resulting from fermentation; and it is +evident that the knowledge of either of these must lead to accurate +conclusions concerning the nature and composition of the other. From +these considerations it became necessary accurately to determine the +constituent elements of the fermentable substances; and for this purpose +I did not make use of the compound juices of fruits, the rigorous +analysis of which is perhaps impossible, but made choice of sugar, which +is easily analysed, and the nature of which I have already explained. +This substance is a true vegetable oxyd, with two bases, composed of +hydrogen and carbon, brought to the state of an oxyd by means of a +certain proportion of oxygen; and these three elements are combined in +such a way that a very slight force is sufficient to destroy the +equilibrium of their connection." + +After giving the details of his analysis of sugar and of the products of +fermentation, Lavoisier continues:-- + +"The effect of the vinous fermentation upon sugar is thus reduced to the +mere separation of its elements into two portions; one part is oxygenated +at the expense of the other, so as to form carbonic acid; while the other +part, being disoxygenated in favour of the latter, is converted into the +combustible substance called alkohol; therefore, if it were possible to +re-unite alkohol and carbonic acid together, we ought to form sugar."[1] + +[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated by +Robert Kerr. Second Edition, 1793 (pp. 186-196).] + +Thus Lavoisier thought he had demonstrated that the carbonic acid and the +alcohol which are produced by the process of fermentation, are equal in +weight to the sugar which disappears; but the application of the more +refined methods of modern chemistry to the investigation of the products +of fermentation by Pasteur, in 1860, proved that this is not exactly +true, and that there is a deficit of from 5 to 7 per cent of the sugar +which is not covered by the alcohol and carbonic acid evolved. The +greater part of this deficit is accounted for by the discovery of two +substances, glycerine and succinic acid, of the existence of which +Lavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent. +still remains to be made good. According to Pasteur, it has been +appropriated by the yeast, but the fact that such appropriation takes +place cannot be said to be actually proved. + +However this may be, there can be no doubt that the constituent elements +of fully 98 per cent. of the sugar which has vanished during fermentation +have simply undergone rearrangement; like the soldiers of a brigade, who +at the word of command divide themselves into the independent regiments +to which they belong. The brigade is sugar, the regiments are carbonic +acid, succinic acid, alcohol, and glycerine. + +From the time of Fabroni, onwards, it has been admitted that the agent by +which this surprising rearrangement of the particles of the sugar is +effected is the yeast. But the first thoroughly conclusive evidence of +the necessity of yeast for the fermentation of sugar was furnished by +Appert, whose method of preserving perishable articles of food excited so +much attention in France at the beginning of this century. Gay-Lussac, in +his "Mémoire sur la Fermentation,"[2] alludes to Appert's method of +preserving beer-wort unfermented for an indefinite time, by simply +boiling the wort and closing the vessel in which the boiling fluid is +contained, in such a way as thoroughly to exclude air; and he shows that, +if a little yeast be introduced into such wort, after it has cooled, the +wort at once begins to ferment, even though every precaution be taken to +exclude air. And this statement has since received full confirmation from +Pasteur. + +[Footnote 2: _Annales de Chimie_, 1810.] + +On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amply +proved that air may be allowed to have free access to beer-wort, without +exciting fermentation, if only efficient precautions are taken to prevent +the entry of particles of yeast along with the air. + +Thus, the truth that the fermentation of a simple solution of sugar in +water depends upon the presence of yeast, rests upon an unassailable +foundation; and the inquiry into the exact nature of the substance which +possesses such a wonderful chemical influence becomes profoundly +interesting. + +The first step towards the solution of this problem was made two +centuries ago by the patient and painstaking Dutch naturalist, +Leeuwenhoek, who in the year 1680 wrote thus:-- + +"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis per +materiam pellucidam fluitantibus, quarm cerevisiam esse censui, constare +observavi: vidi etiam evidentissime, unumquemque hujus fermenti globulum +denuo ex sex distinctis globulis constare, accurate eidem quantitate et +formae, cui globulis sanguinis nostri, respondentibus. + +"Verum talis mihi de horum origine et formatione conceptus formabam; +globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se +constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam +cerevisiam vocare licet, refrigescente, multos ex minimis particulis in +cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae +sexta pars est globuli faecis, et iterum sex ex hisce globulis +conjungi."[3] + +[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.] + +Thus Leeuwenhoek discovered that yeast consists of globules floating in a +fluid; but he thought that they were merely the starchy particles of the +grain from which the wort was made, rearranged. He discovered the fact +that yeast had a definite structure, but not the meaning of the fact. A +century and a half elapsed, and the investigation of yeast was +recommenced almost simultaneously by Cagniard de la Tour in France, and +by Schwann and Kützing in Germany. The French observer was the first to +publish his results; and the subject received at his hands and at those +of his colleague, the botanist Turpin, full and satisfactory +investigation. + +The main conclusions at which they arrived are these. The globular, or +oval, corpuscles which float so thickly in the yeast as to make it muddy, +though the largest are not more than one two-thousandth of an inch in +diameter, and the smallest may measure less than one seven-thousandth of +an inch, are living organisms. They multiply with great rapidity by +giving off minute buds, which soon attain the size of their parent, and +then either become detached or remain united, forming the compound +globules of which Leeuwenhoek speaks, though the constancy of their +arrangement in sixes existed only in the worthy Dutchman's imagination. + +It was very soon made out that these yeast organisms, to which Turpin +gave the name of _Torula cerevisioe_, were more nearly allied to the +lower Fungi than to anything else. Indeed Turpin, and subsequently +Berkeley and Hoffmann, believed that they had traced the development of +the _Torula_ into the well-known and very common mould--the _Penicillium +glaucum_. Other observers have not succeeded in verifying these +statements; and my own observations lead me to believe, that while the +connection between _Torula_ and the moulds is a very close one, it is of +a different nature from that which has been supposed. I have never been +able to trace the development of _Torula_ into a true mould; but it is +quite easy to prove that species of true mould, such as _Penicillium_, +when sown in an appropriate nidus, such as a solution of tartrate of +ammonia and yeast-ash, in water, with or without sugar, give rise to +_Toruloe_, similar in all respects to _T. cerevisioe_, except that they +are, on the average, smaller. Moreover, Bail has observed the development +of a _Torula_ larger than _T. cerevisioe_, from a _Mucor_, a mould allied +to _Penicillium_. + +It follows, therefore, that the _Toruloe_, or organisms of yeast, are +veritable plants; and conclusive experiments have proved that the power +which causes the rearrangement of the molecules of the sugar is +intimately connected with the life and growth of the plant. In fact, +whatever arrests the vital activity of the plant also prevents it from +exciting fermentation. + +Such being the facts with regard to the nature of yeast, and the changes +which it effects in sugar, how are they to be accounted for? Before +modern chemistry had come into existence, Stahl, stumbling, with the +stride of genius, upon the conception which lies at the bottom of all +modern views of the process, put forward the notion that the ferment, +being in a state of internal motion, communicated that motion to the +sugar, and thus caused its resolution into new substances. And Lavoisier, +as we have seen, adopts substantially the same view. But Fabroni, full of +the then novel conception of acids and bases and double decompositions, +propounded the hypothesis that sugar is an oxide with two bases, and the +ferment a carbonate with two bases; that the carbon of the ferment unites +with the oxygen of the sugar, and gives rise to carbonic acid; while the +sugar, uniting with the nitrogen of the ferment, produces a new substance +analogous to opium. This is decomposed by distillation, and gives rise to +alcohol. Next, in 1803, Thénard propounded a hypothesis which partakes +somewhat of the nature of both Stahl's and Fabroni's views. "I do not +believe with Lavoisier," he says, "that all the carbonic acid formed +proceeds from the sugar. How, in that case, could we conceive the action +of the ferment on it? I think that the first portions of the acid are due +to a combination of the carbon of the ferment with the oxygen of the +sugar, and that it is by carrying off a portion of oxygen from the last +that the ferment causes the fermentation to commence--the equilibrium +between the principles of the sugar being disturbed, they combine afresh +to form carbonic acid and alcohol." + +The three views here before us may be familiarly exemplified by supposing +the sugar to be a card-house. According to Stahl, the ferment is somebody +who knocks the table, and shakes the card-house down; according to +Fabroni, the ferment takes out some cards, but puts others in their +places; according to Thénard, the ferment simply takes a card out of the +bottom story, the result of which is that all the others fall. + +As chemistry advanced, facts came to light which put a new face upon +Stahl's hypothesis, and gave it a safer foundation than it previously +possessed. The general nature of these phenomena may be thus stated:--A +body, A, without giving to, or taking from, another body B, any material +particles, causes B to decompose into other substances, C, D, E, the sum +of the weights of which is equal to the weight of B, which decomposes. +Thus, bitter almonds contain two substances, amygdalin and synaptase, +which can be extracted, in a separate state, from the bitter almonds. The +amygdalin thus obtained, if dissolved in water, undergoes no change; but +if a little synaptase be added to the solution, the amygdalin splits up +into bitter almond oil, prussic acid, and a kind of sugar. + +A short time after Cagniard de la Tour discovered the yeast plant, +Liebig, struck with the similarity between this and other such processes +and the fermentation of sugar, put forward the hypothesis that yeast +contains a substance which acts upon sugar, as synaptase acts upon +amygdalin. And as the synaptase is certainly neither organized nor alive, +but a mere chemical substance, Liebig treated Cagniard de la Tour's +discovery with no small contempt, and, from that time to the present, has +steadily repudiated the notion that the decomposition of the sugar is, in +any sense, the result of the vital activity of the _Torula_. But, though +the notion that the _Torula_ is a creature which eats sugar and excretes +carbonic acid and alcohol, which is not unjustly ridiculed in the most +surprising paper that ever made its appearance in a grave scientific +journal,[4] may be untenable, the fact that the _Toruloe_ are alive, and +that yeast does not excite fermentation unless it contains living +_Toruloe_, stands fast. Moreover, of late years, the essential +participation of living organisms in fermentation other than the +alcoholic, has been clearly made out by Pasteur and other chemists. + +[Footnote 4: "Das enträthselte Geheimniss der geistigen Gährung +(Vorlänfige briefliche Mittheilung)" is the title of an anonymous +contribution to Wöhler and Liebig's _Annalen der Pharmacie_ for 1839, in +which a somewhat Rabelaisian imaginary description of the organisation of +the "yeast animals" and of the manner in which their functions are +performed, is given with a circumstantiality worthy of the author of +_Gulliver's Travels_. As a specimen of the writer's humour, his account +of what happens when fermentation comes to an end may suffice. "Sobald +nämlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich +gegenseitig selbst auf, was durch eine eigene Manipulation geschieht; +alles wird verdant bis auf die Eier, welche unverändert durch den +Darmkanal hineingehen; man hat zuletzt wieder gährungsfähige Hefe, +nämlich den Saamen der Thiere, der übrig bleibt."] However, it may be +asked, is there any necessary opposition between the so-called "vital" +and the strictly physico-chemical views of fermentation? It is quite +possible that the living _Torula_ may excite fermentation in sugar, +because it constantly produces, as an essential part of its vital +manifestations, some substance which acts upon the sugar, just as the +synaptase acts upon the amygdalin. Or it may be, that, without the +formation of any such special substance, the physical condition of the +living tissue of the yeast plant is sufficient to effect that small +disturbance of the equilibrium of the particles of the sugar, which +Lavoisier thought sufficient to effect its decomposition. + +Platinum in a very fine state of division--known as platinum black, or +_noir de platine_--has the very singular property of causing alcohol to +change into acetic acid with great rapidity. The vinegar plant, which is +closely allied to the yeast plant, has a similar effect upon dilute +alcohol, causing it to absorb the oxygen of the air, and become converted +into vinegar; and Liebig's eminent opponent, Pasteur, who has done so +much for the theory and the practice of vinegar-making, himself suggests +that in this case-- + +"La cause du phénomène physique qui accompagne la vie de la plante réside +dans un état physique propre, analogue à celui du noir de platine. Mais +il est essentiel de remarquer que cet état physique de la plante est +étroitement lié avec la vie de cette plante."[5] + +[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.] + +Now, if the vinegar plant gives rise to the oxidation of alcohol, on +account of its merely physical constitution, it is at any rate possible +that the physical constitution of the yeast plant may exert a decomposing +influence on sugar. + +But, without presuming to discuss a question which leads us into the very +arcana of chemistry, the present state of speculation upon the _modus +operandi_ of the yeast plant in producing fermentation is represented, on +the one hand, by the Stahlian doctrine, supported by Liebig, according to +which the atoms of the sugar are shaken into new combinations either +directly by the _Toruloe_, or indirectly, by some substance formed by +them; and, on the other hand, by the Thénardian doctrine, supported by +Pasteur, according to which the yeast plant assimilates part of the +sugar, and, in so doing, disturbs the rest, and determines its resolution +into the products of fermentation. Perhaps the two views are not so much +opposed as they seem at first sight to be. + +But the interest which attaches to the influence of the yeast plants upon +the medium in which they live and grow does not arise solely from its +bearing upon the theory of fermentation. So long ago as 1838, Turpin +compared the _Toruloe_ to the ultimate elements of the tissues of animals +and plants--"Les organes élémentaires de leurs tissus, comparables aux +petits végétaux des levures ordinaires, sont aussi les décompositeurs des +substances qui les environnent." + +Almost at the same time, and, probably, equally guided by his study of +yeast, Schwann was engaged in those remarkable investigations into the +form and development of the ultimate structural elements of the tissues +of animals, which led him to recognise their fundamental identity with +the ultimate structural elements of vegetable organisms. + +The yeast plant is a mere sac, or "cell," containing a semi-fluid matter, +and Schwann's microscopic analysis resolved all living organisms, in the +long run, into an aggregation of such sacs or cells, variously modified; +and tended to show, that all, whatever their ultimate complication, begin +their existence in the condition of such simple cells. + +In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_ +as a "cell"; and, in a remarkable note to the passage in which he refers +to the yeast plant, Schwann says:-- + +"I have been unable to avoid mentioning fermentation, because it is the +most fully and exactly known operation of cells, and represents, in the +simplest fashion, the process which is repeated by every cell of the +living body." + +In other words, Schwann conceives that every cell of the living body +exerts an influence on the matter which surrounds and permeates it, +analogous to that which a _Torula_ exerts on the saccharine solution by +which it is bathed. A wonderfully suggestive thought, opening up views of +the nature of the chemical processes of the living body, which have +hardly yet received all the development of which they are capable. + +Kant defined the special peculiarity of the living body to be that the +parts exist for the sake of the whole and the whole for the sake of the +parts. But when Turpin and Schwann resolved the living body into an +aggregation of quasi-independent cells, each, like a _Torula_, leading +its own life and having its own laws of growth and development, the +aggregation being dominated and kept working towards a definite end only +by a certain harmony among these units, or by the superaddition of a +controlling apparatus, such as a nervous system, this conception ceased +to be tenable. The cell lives for its own sake, as well as for the sake +of the whole organism; and the cells which float in the blood, live at +its expense, and profoundly modify it, are almost as much independent +organisms as the _Toruloe_ which float in beer-wort. + +Schwann burdened his enunciation of the "cell theory" with two false +suppositions; the one, that the structures he called "nucleus"[6] and +"cell-wall" are essential to a cell; the other, that cells are usually +formed independently of other cells; but, in 1839, it was a vast and +clear gain to arrive at the conception, that the vital functions of all +the higher animals and plants are the resultant of the forces inherent in +the innumerable minute cells of which they are composed, and that each of +them is, itself, an equivalent of one of the lowest and simplest of +independent living beings--the _Torula_. + +[Footnote 6: Later investigations have thrown an entirely new light upon +the structure and the functional importance of the nucleus; and have +proved that Schwann did not over-estimate its importance. 1894.] + +From purely morphological investigations, Turpin and Schwann, as we have +seen, arrived at the notion of the fundamental unity of structure of +living beings. And, before long, the researches of chemists gradually led +up to the conception of the fundamental unity of their composition. + +So far back as 1803, Thénard pointed out, in most distinct terms, the +important fact that yeast contains a nitrogenous "animal" substance; and +that such a substance is contained in all ferments. Before him, Fabroni +and Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulder +endeavoured to demonstrate that a peculiar substance, which he called +"protein," was essentially characteristic of living matter. + +In 1846, Payen writes:-- + +"Enfin, une loi sans exception me semble apparaître dans les faits +nombreux que j'ai observés et conduire à envisager sous un nouveau jour +la vie végétale; si je ne m'abuse, tout ce que dans les tissus végétaux +la vue directe où amplifiée nous permet de discerner sous la forme de +cellules et de vaisseaux, ne représente autre chose que les enveloppes +protectrices, les réservoirs et les conduits, à l'aide desquels les corps +animés qui les secrètent et les façonnent, se logent, puisent et +charrient leurs aliments, déposent et isolent les matières excrétées." + +And again:-- + +"Afin de compléter aujourd'hui l'énoncé du fait général, je rappellerai +que les corps, doué des fonctions accomplies dans les tissus des plantes, +sont formés des éléments qui constituent, en proportion peu variable, les +organismes animaux; qu'ainsi l'on est conduit à reconnaître une immense +unité de composition élémentaire dans tous les corps vivants de la +nature."[7] + +[Footnote 7: Mém. sur les Développements des Végétaux, &c.--_Mém. +Présentées_. ix. 1846.] + +In the year (1846) in which these remarkable passages were published, the +eminent German botanist, Von Mohl invented the word "protoplasm," as a +name for one portion of those nitrogenous contents of the cells of living +plants, the close chemical resemblance of which to the essential +constituents of living animals is so strongly indicated by Payen. And +through the twenty-five years that have passed, since the matter of life +was first called protoplasm, a host of investigators, among whom Cohn, +Max Schulze, and Kühne must be named as leaders, have accumulated +evidence, morphological, physiological, and chemical, in favour of that +"immense unité de composition élémentaire dans tous les corps vivants de +la nature," into which Payen had, so early, a clear insight. + +As far back as 1850, Cohn wrote, apparently without any knowledge of what +Payen had said before him:-- + +"The protoplasm of the botanist, and the contractile substance and +sarcode of the zoologist, must be, if not identical, yet in a high degree +analogous substances. Hence, from this point of view, the difference +between animals and plants consists in this; that, in the latter, the +contractile substance, as a primordial utricle, is enclosed within an +inert cellulose membrane, which permits it only to exhibit an internal +motion, expressed by the phenomena of rotation and circulation, while, in +the former, it is not so enclosed. The protoplasm in the form of the +primordial utricle is, as it were, the animal element in the plant, but +which is imprisoned, and only becomes free in the animal; or, to strip +off the metaphor which obscures simple thought, the energy of organic +vitality which is manifested in movement is especially exhibited by a +nitrogenous contractile substance, which in plants is limited and +fettered by an inert membrane, in animals not so."[8] + +[Footnote 8: Cohn, "Ueber Protococcus pluvialis," in the _Nova Acta_ for +1850.] + +In 1868, thinking that an untechnical statement of the views current +among the leaders of biological science might be interesting to the +general public, I gave a lecture embodying them in Edinburgh. Those who +have not made the mistake of attempting to approach biology, either by +the high _à priori_ road of mere philosophical speculation, or by the +mere low _à posteriori_ lane offered by the tube of a microscope, but +have taken the trouble to become acquainted with well-ascertained facts +and with their history, will not need to be told that in what I had to +say "as regards protoplasm" in my lecture "On the Physical Basis of Life" +(Vol. I. of these Essays, p. 130), there was nothing new; and, as I hope, +nothing that the present state of knowledge does not justify us in +believing to be true. Under these circumstances, my surprise may be +imagined, when I found, that the mere statement of facts and of views, +long familiar to me as part of the common scientific property of +Continental workers, raised a sort of storm in this country, not only by +exciting the wrath of unscientific persons whose pet prejudices they +seemed to touch, but by giving rise to quite superfluous explosions on +the part of some who should have been better informed. + +Dr. Stirling, for example, made my essay the subject of a special +critical lecture,[9] which I have read with much interest, though, I +confess, the meaning of much of it remains as dark to me as does the +"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr. +Stirling's method of dealing with the subject is peculiar. "Protoplasm" +is a question of history, so far as it is a name; of fact, so far as it +is a thing. Dr. Stirling, has not taken the trouble to refer to the +original authorities for his history, which is consequently a travesty; +and still less has he concerned himself with looking at the facts, but +contents himself with taking them also at second-hand. A most amusing +example of this fashion of dealing with scientific statements is +furnished by Dr. Stirling's remarks upon my account of the protoplasm of +the nettle hair. That account was drawn up from careful and often- +repeated observation of the facts. Dr. Stirling thinks he is offering a +valid criticism, when he says that my valued friend Professor Stricker +gives a somewhat different statement about protoplasm. But why in the +world did not this distinguished Hegelian look at a nettle hair for +himself, before venturing to speak about the matter at all? Why trouble +himself about what either Stricker or I say, when any tyro can see the +facts for himself, if he is provided with those not rare articles, a +nettle and a microscope? But I suppose this would have been +"_Aufklärung_"--a recurrence to the base common-sense philosophy of the +eighteenth century, which liked to see before it believed, and to +understand before it criticised Dr. Stirling winds up his paper with the +following paragraph:-- + +[Footnote 9: Subsequently published under the title of "As regards +Protoplasm."] + +"In short, the whole position of Mr. Huxley, (1) that all organisms +consist alike of the same life-matter, (2) which life-matter is, for its +part, due only to chemistry, must be pronounced untenable--nor less +untenable (3) the materialism he would found on it." + +The paragraph contains three distinct assertions concerning my views, and +just the same number of utter misrepresentations of them. That which I +have numbered (1) turns on the ambiguity of the word "same," for a +discussion of which I would refer Dr. Stirling to a great hero of +"_Aufklärung_" Archbishop Whately; statement number (2) is, in my +judgment, absurd, and certainly I have never said anything resembling it; +while, as to number (3), one great object of my essay was to show that +what is called "materialism" has no sound philosophical basis! + +As we have seen, the study of yeast has led investigators face to face +with problems of immense interest in pure chemistry, and in animal and +vegetable morphology. Its physiology is not less rich in subjects for +inquiry. Take, for example, the singular fact that yeast will increase +indefinitely when grown in the dark, in water containing only tartrate of +ammonia a small percentage of mineral salts and sugar. Out of these +materials the _Toruloe_ will manufacture nitrogenous protoplasm, +cellulose, and fatty matters, in any quantity, although they are wholly +deprived of those rays of the sun, the influence of which is essential to +the growth of ordinary plants. There has been a great deal of speculation +lately, as to how the living organisms buried beneath two or three +thousand fathoms of water, and therefore in all probability almost +deprived of light, live. If any of them possess the same powers as yeast +(and the same capacity for living without light is exhibited by some +other fungi) there would seem to be no difficulty about the matter. + +Of the pathological bearings of the study of yeast, and other such +organisms, I have spoken elsewhere. It is certain that, in some animals, +devastating epidemics are caused by fungi of low order--similar to those +of which _Torula_ is a sort of offshoot. It is certain that such diseases +are propagated by contagion and infection, in just the same way as +ordinary contagious and infectious diseases are propagated. Of course, it +does not follow from this, that all contagious and infectious diseases +are caused by organisms of as definite and independent a character as the +_Torula_; but, I think, it does follow that it is prudent and wise to +satisfy one's self in each particular case, that the "germ theory" cannot +and will not explain the facts, before having recourse to hypotheses +which have no equal support from analogy. + + + +V + + +ON THE FORMATION OF COAL + +[1870] + +The lumps of coal in a coal-scuttle very often have a roughly cubical +form. If one of them be picked out and examined with a little care, it +will be found that its six sides are not exactly alike. Two opposite +sides are comparatively smooth and shining, while the other four are much +rougher, and are marked by lines which run parallel with the smooth +sides. The coal readily splits along these lines, and the split surfaces +thus formed are parallel with the smooth faces. In other words, there is +a sort of rough and incomplete stratification in the lump of coal, as if +it were a book, the leaves of which had stuck together very closely. + +Sometimes the faces along which the coal splits are not smooth, but +exhibit a thin layer of dull, charred-looking substance, which is known +as "mineral charcoal." + +Occasionally one of the faces of a lump of coal will present impressions, +which are obviously those of the stem, or leaves, of a plant; but though +hard mineral masses of pyrites, and even fine mud, may occur here and +there, neither sand nor pebbles are met with. + +When the coal burns, the chief ultimate products of its combustion are +carbonic acid, water, and ammoniacal products, which escape up the +chimney; and a greater or less amount of residual earthy salts, which +take the form of ash. These products are, to a great extent, such as +would result from the burning of so much wood. + +These properties of coal may be made out without any very refined +appliances, but the microscope reveals something more. Black and opaque +as ordinary coal is, slices of it become transparent if they are cemented +in Canada balsam, and rubbed down very thin, in the ordinary way of +making thin sections of non-transparent bodies. But as the thin slices, +made in this way, are very apt to crack and break into fragments, it is +better to employ marine glue as the cementing material. By the use of +this substance, slices of considerable size and of extreme thinness and +transparency may be obtained.[1] + +[Footnote 1: My assistant in the Museum of Practical Geology, Mr. Newton, +invented this excellent method of obtaining thin slices of coal.] + +Now let us suppose two such slices to be prepared from our lump of coal-- +one parallel with the bedding, the other perpendicular to it; and let us +call the one the horizontal, and the other the vertical, section. The +horizontal section will present more or less rounded yellow patches and +streaks, scattered irregularly through the dark brown, or blackish, +ground substance; while the vertical section will exhibit mere elongated +bars and granules of the same yellow materials, disposed in lines which +correspond, roughly, with the general direction of the bedding of the +coal. + +This is the microscopic structure of an ordinary piece of coal. But if a +great series of coals, from different localities and seams, or even from +different parts of the same seam, be examined, this structure will be +found to vary in two directions. In the anthracitic, or stone-coals, +which burn like coke, the yellow matter diminishes, and the ground +substance becomes more predominant, blacker, and more opaque, until it +becomes impossible to grind a section thin enough to be translucent; +while, on the other hand, in such as the "Better-Bed" coal of the +neighbourhood of Bradford, which burns with much flame, the coal is of a +far lighter, colour and transparent sections are very easily obtained. In +the browner parts of this coal, sharp eyes will readily detect multitudes +of curious little coin-shaped bodies, of a yellowish brown colour, +embedded in the dark brown ground substance. On the average, these little +brown bodies may have a diameter of about one-twentieth of an inch. They +lie with their flat surfaces nearly parallel with the two smooth faces of +the block in which they are contained; and, on one side of each, there +may be discerned a figure, consisting of three straight linear marks, +which radiate from the centre of the disk, but do not quite reach its +circumference. In the horizontal section these disks are often converted +into more or less complete rings; while in the vertical sections they +appear like thick hoops, the sides of which have been pressed together. +The disks are, therefore, flattened bags; and favourable sections show +that the three-rayed marking is the expression of three clefts, which +penetrate one wall of the bag. + +The sides of the bags are sometimes closely approximated; but, when the +bags are less flattened, their cavities are, usually, filled with +numerous, irregularly rounded, hollow bodies, having the same kind of +wall as the large ones, but not more than one seven-hundredth of an inch +in diameter. + +In favourable specimens, again, almost the whole ground substance appears +to be made up of similar bodies--more or less carbonized or blackened-- +and, in these, there can be no doubt that, with the exception of patches +of mineral charcoal, here and there, the whole mass of the coal is made +up of an accumulation of the larger and of the smaller sacs. + +But, in one and the same slice, every transition can be observed from +this structure to that which has been described as characteristic of +ordinary coal. The latter appears to rise out of the former, by the +breaking-up and increasing carbonization of the larger and the smaller +sacs. And, in the anthracitic coals, this process appears to have gone to +such a length, as to destroy the original structure altogether, and to +replace it by a completely carbonized substance. + +Thus coal may be said, speaking broadly, to be composed of two +constituents: firstly, mineral charcoal; and, secondly, coal proper. The +nature of the mineral charcoal has long since been determined. Its +structure shows it to consist of the remains of the stems and leaves of +plants, reduced a little more than their carbon. Again, some of the coal +is made up of the crushed and flattened bark, or outer coat, of the stems +of plants, the inner wood of which has completely decayed away. But what +I may term the "saccular matter" of the coal, which, either in its +primary or in its degraded form constitutes by far the greater part of +all the bituminous coals I have examined, is certainly not mineral +charcoal; nor is its structure that of any stem or leaf. Hence its real +nature is at first by no means apparent, and has been the subject of much +discussion. + +The first person who threw any light upon the problem, as far as I have +been able to discover, was the well-known geologist, Professor Morris. It +is now thirty-four years since he carefully described and figured the +coin-shaped bodies, or larger sacs, as I have called them, in a note +appended to the famous paper "On the Coalbrookdale Coal-Field," published +at that time, by the present President of the Geological Society, Mr. +Prestwich. With much sagacity, Professor Morris divined the real nature +of these bodies, and boldly affirmed them to be the spore-cases of a +plant allied to the living club-mosses. + +But discovery sometimes makes a long halt; and it is only a few years +since Mr. Carruthers determined the plant (or rather one of the plants) +which produces these spore-cases, by finding the discoidal sacs still +adherent to the leaves of the fossilized cone which produced them. He +gave the name of _Flemingites gracilis_ to the plant of which the cones +form a part. The branches and stem of this plant are not yet certainly +known, but there is no sort of doubt that it was closely allied to the +_Lepidodendron_, the remains of which abound in the coal formation. The +_Lepidodendra_ were shrubs and trees which put one more in mind of an +_Araucaria_ than of any other familiar plant; and the ends of the +fruiting branches were terminated by cones, or catkins, somewhat like the +bodies so named in a fir, or a willow. These conical fruits, however, did +not produce seeds; but the leaves of which they were composed bore upon +their surfaces sacs full of spores or sporangia, such as those one sees +on the under surface of a bracken leaf. Now, it is these sporangia of the +Lepidodendroid plant _Flemingites_ which were identified by Mr. +Carruthers with the free sporangia described by Professor Morris, which +are the same as the large sacs of which I have spoken. And, more than +this, there is no doubt that the small sacs are the spores, which were +originally contained in the sporangia. + +The living club-mosses are, for the most part, insignificant and creeping +herbs, which, superficially, very closely resemble true mosses, and none +of them reach more than two or three feet in height. But, in their +essential structure, they very closely resemble the earliest +Lepidodendroid trees of the coal: their stems and leaves are similar; so +are their cones; and no less like are the sporangia and spores; while +even in their size, the spores of the _Lepidodendron_ and those of the +existing _Lycopodium_, or club-moss, very closely approach one another. + +Thus, the singular conclusion is forced upon us, that the greater and the +smaller sacs of the "Better-Bed" and other coals, in which the primitive +structure is well preserved, are simply the sporangia and spores of +certain plants, many of which were closely allied to the existing club- +mosses. And if, as I believe, it can be demonstrated that ordinary coal +is nothing but "saccular" coal which has undergone a certain amount of +that alteration which, if continued, would convert it into anthracite; +then, the conclusion is obvious, that the great mass of the coal we burn +is the result of the accumulation of the spores and spore-cases of +plants, other parts of which have furnished the carbonized stems and the +mineral charcoal, or have left their impressions on the surfaces of the +layer. + +Of the multitudinous speculations which, at various times, have been +entertained respecting the origin and mode of formation of coal, several +appear to be negatived, and put out of court, by the structural facts the +significance of which I have endeavoured to explain. These facts, for +example, do not permit us to suppose that coal is an accumulation of +peaty matter, as some have held. + +Again, the late Professor Quekett was one of the first observers who gave +a correct description of what I have termed the "saccular" structure of +coal; and, rightly perceiving that this structure was something quite +different from that of any known plant, he imagined that it proceeded +from some extinct vegetable organism which was peculiarly abundant +amongst the coal-forming plants. But this explanation is at once shown to +be untenable when the smaller and the larger sacs are proved to be spores +or sporangia. + +Some, once more, have imagined that coal was of submarine origin; and +though the notion is amply and easily refuted by other considerations, it +may be worth while to remark, that it is impossible to comprehend how a +mass of light and resinous spores should have reached the bottom of the +sea, or should have stopped in that position if they had got there. + +At the same time, it is proper to remark that I do not presume to suggest +that all coal must needs have the same structure; or that there may not +be coals in which the proportions of wood and spores, or spore-cases, are +very different from those which I have examined. All I repeat is, that +none of the coals which have come under my notice have enabled me to +observe such a difference. But, according to Principal Dawson, who has so +sedulously examined the fossil remains of plants in North America, it is +otherwise with the vast accumulations of coal in that country. + +"The true coal," says Dr. Dawson, "consists principally of the flattened +bark of Sigillarioid and other trees, intermixed with leaves of Ferns and +_Cordaites_, and other herbaceous _débris_, and with fragments of decayed +wood, constituting 'mineral charcoal,' all these materials having +manifestly alike grown and accumulated where we find them."[2] + +[Footnote 2: _Acadian Geology_, 2nd edition, p. 135.] + +When I had the pleasure of seeing Principal Dawson in London last summer, +I showed him my sections of coal, and begged him to re-examine some of +the American coals on his return to Canada, with an eye to the presence +of spores and sporangia, such as I was able to show him in our English +and Scotch coals. He has been good enough to do so; and in a letter dated +September 26th, 1870, he informs me that-- + +"Indications of spore-cases are rare, except in certain coarse shaly +coals and portions of coals, and in the roofs of the seams. The most +marked case I have yet met with is the shaly coal referred to as +containing _Sporangites_ in my paper on the conditions of accumulation of +coal ("Journal of the Geological Society," vol. xxii. pp. 115, 139, and +165). The purer coals certainly consist principally of cubical tissues +with some true woody matter, and the spore-cases, &c., are chiefly in the +coarse and shaly layers. This is my old doctrine in my two papers in the +"Journal of the Geological Society," and I see nothing to modify it. Your +observations, however, make it probable that the frequent _clear spots_ +in the cannels are spore-cases." + +Dr. Dawson's results are the more remarkable, as the numerous specimens +of British coal, from various localities, which I have examined, tell one +tale as to the predominance of the spore and sporangium element in their +composition; and as it is exactly in the finest and purest coals, such as +the "Better-Bed" coal of Lowmoor, that the spores and sporangia obviously +constitute almost the entire mass of the deposit. + +Coal, such as that which has been described, is always found in sheets, +or "seams," varying from a fraction of an inch to many feet in thickness, +enclosed in the substance of the earth at very various depths, between +beds of rock of different kinds. As a rule, every seam of coal rests upon +a thicker, or thinner, bed of clay, which is known as "under-clay." These +alternations of beds of coal, clay, and rock may be repeated many times, +and are known as the "coal-measures"; and in some regions, as in South +Wales and in Nova Scotia, the coal-measures attain a thickness of twelve +or fourteen thousand feet, and enclose eighty or a hundred seams of coal, +each with its under-clay, and separated from those above and below by +beds of sandstone and shale. + +The position of the beds which constitute the coal-measures is infinitely +diverse. Sometimes they are tilted up vertically, sometimes they are +horizontal, sometimes curved into great basins; sometimes they come to +the surface, sometimes they are covered up by thousands of feet of rock. +But, whatever their present position, there is abundant and conclusive +evidence that every under-clay was once a surface soil. Not only do +carbonized root-fibres frequently abound in these under-clays; but the +stools of trees, the trunks of which are broken off and confounded with +the bed of coal, have been repeatedly found passing into radiating roots, +still embedded in the under-clay. On many parts of the coast of England, +what are commonly known as "submarine forests" are to be seen at low +water. They consist, for the most part, of short stools of oak, beech, +and fir-trees, still fixed by their long roots in the bed of blue clay in +which they originally grew. If one of these submarine forest beds should +be gradually depressed and covered up by new deposits, it would present +just the same characters as an under-clay of the coal, if the +_Sigillaria_ and _Lepidodendron_ of the ancient world were substituted +for the oak, or the beech, of our own times. + +In a tropical forest, at the present day, the trunks of fallen trees, and +the stools of such trees as may have been broken by the violence of +storms, remain entire for but a short time. Contrary to what might be +expected, the dense wood of the tree decays, and suffers from the ravages +of insects, more swiftly than the bark. And the traveller, setting his +foot on a prostrate trunk, finds that it is a mere shell, which breaks +under his weight, and lands his foot amidst the insects, or the reptiles, +which have sought food or refuge within. + +The trees of the coal forests present parallel conditions. When the +fallen trunks which have entered into the composition of the bed of coal +are identifiable, they are mere double shells of bark, flattened together +in consequence of the destruction of the woody core; and Sir Charles +Lyell and Principal Dawson discovered, in the hollow stools of coal trees +of Nova Scotia, the remains of snails, millipedes, and salamander-like +creatures, embedded in a deposit of a different character from that which +surrounded the exterior of the trees. Thus, in endeavouring to comprehend +the formation of a seam of coal, we must try to picture to ourselves a +thick forest, formed for the most part of trees like gigantic club- +mosses, mares'-tails, and tree-ferns, with here and there some that had +more resemblance to our existing yews and fir-trees. We must suppose +that, as the seasons rolled by, the plants grew and developed their +spores and seeds; that they shed these in enormous quantities, which +accumulated on the ground beneath; and that, every now and then, they +added a dead frond or leaf; or, at longer intervals, a rotten branch, or +a dead trunk, to the mass. + +A certain proportion of the spores and seeds no doubt fulfilled their +obvious function, and, carried by the wind to unoccupied regions, +extended the limits of the forest; many might be washed away by rain into +streams, and be lost; but a large portion must have remained, to +accumulate like beech-mast, or acorns, beneath the trees of a modern +forest. + +But, in this case it may be asked, why does not our English coal consist +of stems and leaves to a much greater extent than it does? What is the +reason of the predominance of the spores and spore-cases in it? + +A ready answer to this question is afforded by the study of a living +full-grown club-moss. Shake it upon a piece of paper, and it emits a +cloud of fine dust, which falls over the paper, and is the well-known +Lycopodium powder. Now this powder used to be, and I believe still is, +employed for two objects which seem, at first sight, to have no +particular connection with one another. It is, or was, employed in making +lightning, and in making pills. The coats of the spores contain so much +resinous matter, that a pinch of Lycopodium powder, thrown through the +flame of a candle, burns with an instantaneous flash, which has long done +duty for lightning on the stage. And the same character makes it a +capital coating for pills; for the resinous powder prevents the drug from +being wetted by the saliva, and thus bars the nauseous flavour from the +sensitive papilla; of the tongue. + +But this resinous matter, which lies in the walls of the spores and +sporangia, is a substance not easily altered by air and water, and hence +tends to preserve these bodies, just as the bituminized cerecloth +preserves an Egyptian mummy; while, on the other hand, the merely woody +stem and leaves tend to rot, as fast as the wood of the mummy's coffin +has rotted. Thus the mixed heap of spores, leaves, and stems in the coal- +forest would be persistently searched by the long-continued action of air +and rain; the leaves and stems would gradually be reduced to little but +their carbon, or, in other words, to the condition of mineral charcoal in +which we find them; while the spores and sporangia remained as a +comparatively unaltered and compact residuum. + +There is, indeed, tolerably clear evidence that the coal must, under some +circumstances, have been converted into a substance hard enough to be +rolled into pebbles, while it yet lay at the surface of the earth; for in +some seams of coal, the courses of rivulets, which must have been living +water, while the stratum in which their remains are found was still at +the surface, have been observed to contain rolled pebbles of the very +coal through which the stream has cut its way. + +The structural facts are such as to leave no alternative but to adopt the +view of the origin of such coal as I have described, which has just been +stated; but, happily, the process is not without analogy at the present +day. I possess a specimen of what is called "white coal" from Australia. +It is an inflammable material, burning with a bright flame and having +much the consistence and appearance of oat-cake, which, I am informed +covers a considerable area. It consists, almost entirely, of a compacted +mass of spores and spore-cases. But the fine particles of blown sand +which are scattered through it, show that it must have accumulated, +subaërially, upon the surface of a soil covered by a forest of +cryptogamous plants, probably tree-ferns. + +As regards this important point of the subaërial region of coal, I am +glad to find myself in entire accordance with Principal Dawson, who bases +his conclusions upon other, but no less forcible, considerations. In a +passage, which is the continuation of that already cited, he writes:-- + +"(3) The microscopical structure and chemical composition of the beds of +cannel coal and earthy bitumen, and of the more highly bituminous and +carbonaceous shale, show them to have been of the nature of the fine +vegetable mud which accumulates in the ponds and shallow lakes of modern +swamps. When such tine vegetable sediment is mixed, as is often the case, +with clay, it becomes similar to the bituminous limestone and calcareo- +bituminous shales of the coal-measures. (4) A few of the under-clays, +which support beds of coal, are of the nature of the vegetable mud above +referred to; but the greater part are argillo-arenaceous in composition, +with little vegetable matter, and bleached by the drainage from them of +water containing the products of vegetable decay. They are, in short, +loamy or clay soils, and must have been sufficiently above water to admit +of drainage. The absence of sulphurets, and the occurrence of carbonate +of iron in connection with them, prove that, when they existed as soils, +rain-water, and not sea-water, percolated them. (5) The coal and the +fossil forests present many evidences of subaërial conditions. Most of +the erect and prostrate trees had become hollow shells of bark before +they were finally embedded, and their wood had broken into cubical pieces +of mineral charcoal. Land-snails and galley-worms (_Xylobius_) crept into +them, and they became dens, or traps, for reptiles. Large quantities of +mineral charcoal occur on the surface of all the large beds of coal. None +of these appearances could have been produced by subaqueous action. (6) +Though the roots of the _Sigillaria_ bear more resemblance to the +rhizomes of certain aquatic plants; yet, structurally, they are +absolutely identical with the roots of Cycads, which the stems also +resemble. Further, the _Sigillarioe_ grew on the same soils which +supported Conifers, _Lepidodendra_, _Cordaites_, and Ferns-plants which +could not have grown in water. Again, with the exception perhaps of some +_Pinnularioe_, and _Asterophyllites_, there is a remarkable absence from +the coal measures of any form of properly aquatic vegetation. (7) The +occurrence of marine, or brackish-water animals, in the roofs of coal- +beds, or even in the coal itself, affords no evidence of subaqueous +accumulation, since the same thing occurs in the case of modern submarine +forests. For these and other reasons, some of which are more fully stated +in the papers already referred to, while I admit that the areas of coal +accumulation were frequently submerged, I must maintain that the true +coal is a subaërial accumulation by vegetable growth on soils, wet and +swampy it is true, but not submerged." + +I am almost disposed to doubt whether it is necessary to make the +concession of "wet and swampy"; otherwise, there is nothing that I know +of to be said against this excellent conspectus of the reasons for +believing in the subaërial origin of coal. + +But the coal accumulated upon the area covered by one of the great +forests of the carboniferous epoch would in course of time, have been +wasted away by the small, but constant, wear and tear of rain and streams +had the land which supported it remained at the same level, or been +gradually raised to a greater elevation. And, no doubt, as much coal as +now exists has been destroyed, after its formation, in this way. What are +now known as coal districts owe their importance to the fact that they +were areas of slow depression, during a greater or less portion of the +carboniferous epoch; and that, in virtue of this circumstance, Mother +Earth was enabled to cover up her vegetable treasures, and preserve them +from destruction. + +Wherever a coal-field now exists, there must formerly have been free +access for a great river, or for a shallow sea, bearing sediment in the +shape of sand and mud. When the coal-forest area became slowly depressed, +the waters must have spread over it, and have deposited their burden upon +the surface of the bed of coal, in the form of layers, which are now +converted into shale, or sandstone. Then followed a period of rest, in +which the superincumbent shallow waters became completely filled up, and +finally replaced, by fine mud, which settled down into a new under-clay, +and furnished the soil for a fresh forest growth. This flourished, and +heaped up its spores and wood into coal, until the stage of slow +depression recommenced. And, in some localities, as I have mentioned, the +process was repeated until the first of the alternating beds had sunk to +near three miles below its original level at the surface of the earth. + +In reflecting on the statement, thus briefly made, of the main facts +connected with the origin of the coal formed during the carboniferous +epoch, two or three considerations suggest themselves. + +In the first place, the great phantom of geological time rises before the +student of this, as of all other, fragments of the history of our earth-- +springing irrepressibly out of the facts, like the Djin from the jar +which the fishermen so incautiously opened; and like the Djin again, +being vaporous, shifting, and indefinable, but unmistakably gigantic. +However modest the bases of one's calculation may be, the minimum of time +assignable to the coal period remains something stupendous. + +Principal Dawson is the last person likely to be guilty of exaggeration +in this matter, and it will be well to consider what he has to say about +it:-- + +"The rate of accumulation of coal was very slow. The climate of the +period, in the northern temperate zone, was of such a character that the +true conifers show rings of growth, not larger, nor much less distinct, +than those of many of their modern congeners. The _Sigillarioe_ and +_Calamites_ were not, as often supposed, composed wholly, or even +principally, of lax and soft tissues, or necessarily short-lived. The +former had, it is true, a very thick inner bark; but their dense woody +axis, their thick and nearly imperishable outer bark, and their scanty +and rigid foliage, would indicate no very rapid growth or decay. In the +case of the _Sigillarioe_, the variations in the leaf-scars in different +parts of the trunk, the intercalation of new ridges at the surface +representing that of new woody wedges in the axis, the transverse marks +left by the stages of upward growth, all indicate that several years must +have been required for the growth of stems of moderate size. The enormous +roots of these trees, and the condition of the coal-swamps, must have +exempted them from the danger of being overthrown by violence. They +probably fell in successive generations from natural decay; and making +every allowance for other materials, we may safely assert that every foot +of thickness of pure bituminous coal implies the quiet growth and fall of +at least fifty generations of _Sigillarioe_, and therefore an undisturbed +condition of forest growth enduring through many centuries. Further, +there is evidence that an immense amount of loose parenchymatous tissue, +and even of wood, perished by decay, and we do not know to what extent +even the most durable tissues may have disappeared in this way; so that, +in many coal-seams, we may have only a very small part of the vegetable +matter produced." + +Undoubtedly the force of these reflections is not diminished when the +bituminous coal, as in Britain, consists of accumulated spores and spore- +cases, rather than of stems. But, suppose we adopt Principal Dawson's +assumption, that one foot of coal represents fifty generations of coal +plants; and, further, make the moderate supposition that each generation +of coal plants took ten years to come to maturity--then, each foot- +thickness of coal represents five hundred years. The superimposed beds of +coal in one coal-field may amount to a thickness of fifty or sixty feet, +and therefore the coal alone, in that field, represents 500 x 50 = 25,000 +years. But the actual coal is but an insignificant portion of the total +deposit, which, as has been seen, may amount to between two and three +miles of vertical thickness. Suppose it be 12,000 feet--which is 240 +times the thickness of the actual coal--is there any reason why we should +believe it may not have taken 240 times as long to form? I know of none. +But, in this case, the time which the coal-field represents would be +25,000 x 240 = 6,000,000 years. As affording a definite chronology, of +course such calculations as these are of no value; but they have much use +in fixing one's attention upon a possible minimum. A man may be puzzled +if he is asked how long Rome took a-building; but he is proverbially safe +if he affirms it not to have been built in a day; and our geological +calculations are all, at present, pretty much on that footing. + +A second consideration which the study of the coal brings prominently +before the mind of any one who is familiar with palaeontology is, that the +coal Flora, viewed in relation to the enormous period of time which it +lasted, and to the still vaster period which has elapsed since it +flourished, underwent little change while it endured, and in its peculiar +characters, differs strangely little from that which at present exist. + +The same species of plants are to be met with throughout the whole +thickness of a coal-field, and the youngest are not sensibly different +from the oldest. But more than this. Notwithstanding that the +carboniferous period is separated from us by more than the whole time +represented by the secondary and tertiary formations, the great types of +vegetation were as distinct then as now. The structure of the modern +club-moss furnishes a complete explanation of the fossil remains of the +_Lepidodendra_, and the fronds of some of the ancient ferns are hard to +distinguish from existing ones. At the same time, it must be remembered, +that there is nowhere in the world, at present, any _forest_ which bears +more than a rough analogy with a coal-forest. The types may remain, but +the details of their form, their relative proportions, their associates, +are all altered. And the tree-fern forest of Tasmania, or New Zealand, +gives one only a faint and remote image of the vegetation of the ancient +world. + +Once more, an invariably-recurring lesson of geological history, at +whatever point its study is taken up: the lesson of the almost infinite +slowness of the modification of living forms. The lines of the pedigrees +of living things break off almost before they begin to converge. + +Finally, yet another curious consideration. Let us suppose that one of +the stupid, salamander-like Labyrinthodonts, which pottered, with much +belly and little leg, like Falstaff in his old age, among the coal- +forests, could have had thinking power enough in his small brain to +reflect upon the showers of spores which kept on falling through years +and centuries, while perhaps not one in ten million fulfilled its +apparent purpose, and reproduced the organism which gave it birth: surely +he might have been excused for moralizing upon the thoughtless and wanton +extravagance which Nature displayed in her operations. + +But we have the advantage over our shovel-headed predecessor--or possibly +ancestor--and can perceive that a certain vein of thrift runs through +this apparent prodigality. Nature is never in a hurry, and seems to have +had always before her eyes the adage, "Keep a thing long enough, and you +will find a use for it." She has kept her beds of coal many millions of +years without being able to find much use for them; she has sent them +down beneath the sea, and the sea-beasts could make nothing of them; she +has raised them up into dry land, and laid the black veins bare, and +still, for ages and ages, there was no living thing on the face of the +earth that could see any sort of value in them; and it was only the other +day, so to speak, that she turned a new creature out of her workshop, who +by degrees acquired sufficient wits to make a fire, and then to discover +that the black rock would burn. + +I suppose that nineteen hundred years ago, when Julius Caesar was good +enough to deal with Britain as we have dealt with New Zealand, the +primaeval Briton, blue with cold and woad, may have known that the strange +black stone, of which he found lumps here and there in his wanderings, +would burn, and so help to warm his body and cook his food. Saxon, Dane, +and Norman swarmed into the land. The English people grew into a powerful +nation, and Nature still waited for a full return of the capital she had +invested in the ancient club-mosses. The eighteenth century arrived, and +with it James Watt. The brain of that man was the spore out of which was +developed the modern steam-engine, and all the prodigious trees and +branches of modern industry which have grown out of this. But coal is as +much an essential condition of this growth and development as carbonic +acid is for that of a club-moss. Wanting coal, we could not have smelted +the iron needed to make our engines, nor have worked our engines when we +had got them. But take away the engines, and the great towns of Yorkshire +and Lancashire vanish like a dream. Manufactures give place to +agriculture and pasture, and not ten men can live where now ten thousand +are amply supported. + +Thus, all this abundant wealth of money and of vivid life is Nature's +interest upon her investment in club-mosses, and the like, so long ago. +But what becomes of the coal which is burnt in yielding this interest? +Heat comes out of it, light comes out of it; and if we could gather +together all that goes up the chimney, and all that remains in the grate +of a thoroughly-burnt coal-fire, we should find ourselves in possession +of a quantity of carbonic acid, water, ammonia, and mineral matters, +exactly equal in weight to the coal. But these are the very matters with +which Nature supplied the club-mosses which made the coal She is paid +back principal and interest at the same time; and she straightway invests +the carbonic acid, the water, and the ammonia in new forms of life, +feeding with them the plants that now live. Thrifty Nature! Surely no +prodigal, but most notable of housekeepers! + + + +VI + + +ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS + +[1876] + +In the whole history of science there is nothing more remarkable than the +rapidity of the growth of biological knowledge within the last half- +century, and the extent of the modification which has thereby been +effected in some of the fundamental conceptions of the naturalist. + +In the second edition of the "Règne Animal," published in 1828, Cuvier +devotes a special section to the "Division of Organised Beings into +Animals and Vegetables," in which the question is treated with that +comprehensiveness of knowledge and clear critical judgment which +characterise his writings, and justify us in regarding them as +representative expressions of the most extensive, if not the profoundest, +knowledge of his time. He tells us that living beings have been +subdivided from the earliest times into _animated beings_, which possess +sense and motion, and _inanimated beings_, which are devoid of these +functions and simply vegetate. + +Although the roots of plants direct themselves towards moisture, and +their leaves towards air and light,--although the parts of some plants +exhibit oscillating movements without any perceptible cause, and the +leaves of others retract when touched,--yet none of these movements +justify the ascription to plants of perception or of will. From the +mobility of animals, Cuvier, with his characteristic partiality for +teleological reasoning, deduces the necessity of the existence in them of +an alimentary cavity, or reservoir of food, whence their nutrition may be +drawn by the vessels, which are a sort of internal roots; and, in the +presence of this alimentary cavity, he naturally sees the primary and the +most important distinction between animals and plants. + +Following out his teleological argument, Cuvier remarks that the +organisation of this cavity and its appurtenances must needs vary +according to the nature of the aliment, and the operations which it has +to undergo, before it can be converted into substances fitted for +absorption; while the atmosphere and the earth supply plants with juices +ready prepared, and which can be absorbed immediately. As the animal body +required to be independent of heat and of the atmosphere, there were no +means by which the motion of its fluids could be produced by internal +causes. Hence arose the second great distinctive character of animals, or +the circulatory system, which is less important than the digestive, since +it was unnecessary, and therefore is absent, in the more simple animals. + +Animals further needed muscles for locomotion and nerves for sensibility. +Hence, says Cuvier, it was necessary that the chemical composition of the +animal body should be more complicated than that of the plant; and it is +so, inasmuch as an additional substance, nitrogen, enters into it as an +essential element; while, in plants, nitrogen is only accidentally joined +with he three other fundamental constituents of organic beings--carbon, +hydrogen, and oxygen. Indeed, he afterwards affirms that nitrogen is +peculiar to animals; and herein he places the third distinction between +the animal and the plant. The soil and the atmosphere supply plants with +water, composed of hydrogen and oxygen; air, consisting of nitrogen and +oxygen; and carbonic acid, containing carbon and oxygen. They retain the +hydrogen and the carbon, exhale the superfluous oxygen, and absorb little +or no nitrogen. The essential character of vegetable life is the +exhalation of oxygen, which is effected through the agency of light. +Animals, on the contrary, derive their nourishment either directly or +indirectly from plants. They get rid of the superfluous hydrogen and +carbon, and accumulate nitrogen. The relations of plants and animals to +the atmosphere are therefore inverse. The plant withdraws water and +carbonic acid from the atmosphere, the animal contributes both to it. +Respiration--that is, the absorption of oxygen and the exhalation of +carbonic acid--is the specially animal function of animals, and +constitutes their fourth distinctive character. + +Thus wrote Cuvier in 1828. But, in the fourth and fifth decades of this +century, the greatest and most rapid revolution which biological science +has ever undergone was effected by the application of the modern +microscope to the investigation of organic structure; by the introduction +of exact and easily manageable methods of conducting the chemical +analysis of organic compounds; and finally, by the employment of +instruments of precision for the measurement of the physical forces which +are at work in the living economy. + +That the semi-fluid contents (which we now term protoplasm) of the cells +of certain plants, such as the _Charoe_ are in constant and regular +motion, was made out by Bonaventura Corti a century ago; but the fact, +important as it was, fell into oblivion, and had to be rediscovered by +Treviranus in 1807. Robert Brown noted the more complex motions of the +protoplasm in the cells of _Tradescantia_ in 1831; and now such movements +of the living substance of plants are well known to be some of the most +widely-prevalent phenomena of vegetable life. + +Agardh, and other of the botanists of Cuvier's generation, who occupied +themselves with the lower plants, had observed that, under particular +circumstances, the contents of the cells of certain water-weeds were set +free, and moved about with considerable velocity, and with all the +appearances of spontaneity, as locomotive bodies, which, from their +similarity to animals of simple organisation, were called "zoospores." +Even as late as 1845, however, a botanist of Schleiden's eminence dealt +very sceptically with these statements; and his scepticism was the more +justified, since Ehrenberg, in his elaborate and comprehensive work on +the _Infusoria_, had declared the greater number of what are now +recognised as locomotive plants to be animals. + +At the present day, innumerable plants and free plant cells are known to +pass the whole or part of their lives in an actively locomotive +condition, in no wise distinguishable from that of one of the simpler +animals; and, while in this condition, their movements are, to all +appearance, as spontaneous--as much the product of volition--as those of +such animals. + +Hence the teleological argument for Cuvier's first diagnostic character-- +the presence in animals of an alimentary cavity, or internal pocket, in +which they can carry about their nutriment--has broken down, so far, at +least, as his mode of stating it goes. And, with the advance of +microscopic anatomy, the universality of the fact itself among animals +has ceased to be predicable. Many animals of even complex structure, +which live parasitically within others, are wholly devoid of an +alimentary cavity. Their food is provided for them, not only ready +cooked, but ready digested, and the alimentary canal, become superfluous, +has disappeared. Again, the males of most Rotifers have no digestive +apparatus; as a German naturalist has remarked, they devote themselves +entirely to the "Minnedienst," and are to be reckoned among the few +realisations of the Byronic ideal of a lover. Finally, amidst the lowest +forms of animal life, the speck of gelatinous protoplasm, which +constitutes the whole body, has no permanent digestive cavity or mouth, +but takes in its food anywhere; and digests, so to speak, all over its +body. But although Cuvier's leading diagnosis of the animal from the +plant will not stand a strict test, it remains one of the most constant +of the distinctive characters of animals. And, if we substitute for the +possession of an alimentary cavity, the power of taking solid nutriment +into the body and there digesting it, the definition so changed will +cover all animals except certain parasites, and the few and exceptional +cases of non-parasitic animals which do not feed at all. On the other +hand, the definition thus amended will exclude all ordinary vegetable +organisms. + +Cuvier himself practically gives up his second distinctive mark when he +admits that it is wanting in the simpler animals. + +The third distinction is based on a completely erroneous conception of +the chemical differences and resemblances between the constituents of +animal and vegetable organisms, for which Cuvier is not responsible, as +it was current among contemporary chemists. It is now established that +nitrogen is as essential a constituent of vegetable as of animal living +matter; and that the latter is, chemically speaking, just as complicated +as the former. Starchy substances, cellulose and sugar, once supposed to +be exclusively confined to plants, are now known to be regular and normal +products of animals. Amylaceous and saccharine substances are largely +manufactured, even by the highest animals; cellulose is widespread as a +constituent of the skeletons of the lower animals; and it is probable +that amyloid substances are universally present in the animal organism, +though not in the precise form of starch. + +Moreover, although it remains true that there is an inverse relation +between the green plant in sunshine and the animal, in so far as, under +these circumstances, the green plant decomposes carbonic acid and exhales +oxygen, while the animal absorbs oxygen and exhales carbonic acid; yet, +the exact researches of the modern chemical investigators of the +physiological processes of plants have clearly demonstrated the fallacy +of attempting to draw any general distinction between animals and +vegetables on this ground. In fact, the difference vanishes with the +sunshine, even in the case of the green plant; which, in the dark, +absorbs oxygen and gives out carbonic acid like any animal.[1] On the +other hand, those plants, such as the fungi, which contain no chlorophyll +and are not green, are always, so far as respiration is concerned, in the +exact position of animals. They absorb oxygen and give out carbonic acid. + +[Footnote 1: There is every reason to believe that living plants, like +living animals, always respire, and, in respiring, absorb oxygen and give +off carbonic acid; but, that in green plants exposed to daylight or to +the electric light, the quantity of oxygen evolved in consequence of the +decomposition of carbonic acid by a special apparatus which green plants +possess exceeds that absorbed in the concurrent respiratory process.] + +Thus, by the progress of knowledge, Cuvier's fourth distinction between +the animal and the plant has been as completely invalidated as the third +and second; and even the first can be retained only in a modified form +and subject to exceptions. + +But has the advance of biology simply tended to break down old +distinctions, without establishing new ones? + +With a qualification, to be considered presently, the answer to this +question is undoubtedly in the affirmative. The famous researches of +Schwann and Schleiden in 1837 and the following years, founded the modern +science of histology, or that branch of anatomy which deals with the +ultimate visible structure of organisms, as revealed by the microscope; +and, from that day to this, the rapid improvement of methods of +investigation, and the energy of a host of accurate observers, have given +greater and greater breadth and firmness to Schwann's great +generalisation, that a fundamental unity of structure obtains in animals +and plants; and that, however diverse may be the fabrics, or _tissues_, +of which their bodies are composed, all these varied structures result +from the metamorphosis of morphological units (termed _cells_, in a more +general sense than that in which the word "cells" was at first employed), +which are not only similar in animals and in plants respectively, but +present a close resemblance, when those of animals and those of plants +are compared together. + +The contractility which is the fundamental condition of locomotion, has +not only been discovered to exist far more widely among plants than was +formerly imagined; but, in plants, the act of contraction has been found +to be accompanied, as Dr. Burdon Sanderson's interesting investigations +have shown, by a disturbance of the electrical state of the contractile +substance, comparable to that which was found by Du Bois Reymond to be a +concomitant of the activity of ordinary muscle in animals. + +Again, I know of no test by which the reaction of the leaves of the +Sundew and of other plants to stimuli, so fully and carefully studied by +Mr. Darwin, can be distinguished from those acts of contraction following +upon stimuli, which are called "reflex" in animals. + +On each lobe of the bilobed leaf of Venus's fly-trap (_Dionoea +muscipula_) are three delicate filaments which stand out at right angle +from the surface of the leaf. Touch one of them with the end of a fine +human hair and the lobes of the leaf instantly close together[2] in +virtue of an act of contraction of part of their substance, just as the +body of a snail contracts into its shell when one of its "horns" is +irritated. + +[Footnote 2: Darwin, _Insectivorous Plants_, p. 289.] + +The reflex action of the snail is the result of the presence of a nervous +system in the animal. A molecular change takes place in the nerve of the +tentacle, is propagated to the muscles by which the body is retracted, +and causing them to contract, the act of retraction is brought about. Of +course the similarity of the acts does not necessarily involve the +conclusion that the mechanism by which they are effected is the same; but +it suggests a suspicion of their identity which needs careful testing. + +The results of recent inquiries into the structure of the nervous system +of animals converge towards the conclusion that the nerve fibres, which +we have hitherto regarded as ultimate elements of nervous tissue, are not +such, but are simply the visible aggregations of vastly more attenuated +filaments, the diameter of which dwindles down to the limits of our +present microscopic vision, greatly as these have been extended by modern +improvements of the microscope; and that a nerve is, in its essence, +nothing but a linear tract of specially modified protoplasm between two +points of an organism--one of which is able to affect the other by means +of the communication so established. Hence, it is conceivable that even +the simplest living being may possess a nervous system. And the question +whether plants are provided with a nervous system or not, thus acquires a +new aspect, and presents the histologist and physiologist with a problem +of extreme difficulty, which must be attacked from a new point of view +and by the aid of methods which have yet to be invented. + +Thus it must be admitted that plants may be contractile and locomotive; +that, while locomotive, their movements may have as much appearance of +spontaneity as those of the lowest animals; and that many exhibit +actions, comparable to those which are brought about by the agency of a +nervous system in animals. And it must be allowed to be possible that +further research may reveal the existence of something comparable to a +nervous system in plants. So that I know not where we can hope to find +any absolute distinction between animals and plants, unless we return to +their mode of nutrition, and inquire whether certain differences of a +more occult character than those imagined to exist by Cuvier, and which +certainly hold good for the vast majority of animals and plants, are of +universal application. + +A bean may be supplied with water in which salts of ammonia and certain +other mineral salts are dissolved in due proportion; with atmospheric air +containing its ordinary minute dose of carbonic acid; and with nothing +else but sunlight and heat. Under these circumstances, unnatural as they +are, with proper management, the bean will thrust forth its radicle and +its plumule; the former will grow down into roots, the latter grow up +into the stem and leaves of a vigorous bean-plant; and this plant will, +in due time, flower and produce its crop of beans, just as if it were +grown in the garden or in the field. + +The weight of the nitrogenous protein compounds, of the oily, starchy, +saccharine and woody substances contained in the full-grown plant and its +seeds, will be vastly greater than the weight of the same substances +contained in the bean from which it sprang. But nothing has been supplied +to the bean save water, carbonic acid, ammonia, potash, lime, iron, and +the like, in combination with phosphoric, sulphuric, and other acids. +Neither protein, nor fat, nor starch, nor sugar, nor any substance in the +slightest degree resembling them, has formed part of the food of the +bean. But the weights of the carbon, hydrogen, oxygen, nitrogen, +phosphorus, sulphur, and other elementary bodies contained in the bean- +plant, and in the seeds which it produces, are exactly equivalent to the +weights of the same elements which have disappeared from the materials +supplied to the bean during its growth. Whence it follows that the bean +has taken in only the raw materials of its fabric, and has manufactured +them into bean-stuffs. + +The bean has been able to perform this great chemical feat by the help of +its green colouring matter, or chlorophyll; for it is only the green +parts of the plant which, under the influence of sunlight, have the +marvellous power of decomposing carbonic acid, setting free the oxygen +and laying hold of the carbon which it contains. In fact, the bean +obtains two of the absolutely indispensable elements of its substance +from two distinct sources; the watery solution, in which its roots are +plunged, contains nitrogen but no carbon; the air, to which the leaves +are exposed, contains carbon, but its nitrogen is in the state of a free +gas, in which condition the bean can make no use of it;[3] and the +chlorophyll[4] is the apparatus by which the carbon is extracted from the +atmospheric carbonic acid--the leaves being the chief laboratories in +which this operation is effected. + +[Footnote 3: I purposely assume that the air with which the bean is +supplied in the case stated contains no ammoniacal salts.] + +[Footnote 4: The recent researches of Pringsheim have raised a host of +questions as to the exact share taken by chlorophyll in the chemical +operations which are effected by the green parts of plants. It may be +that the chlorophyll is only a constant concomitant of the actual +deoxidising apparatus.] + +The great majority of conspicuous plants are, as everybody knows, green; +and this arises from the abundance of their chlorophyll. The few which +contain no chlorophyll and are colourless, are unable to extract the +carbon which they require from atmospheric carbonic acid, and lead a +parasitic existence upon other plants; but it by no means follows, often +as the statement has been repeated, that the manufacturing power of +plants depends on their chlorophyll, and its interaction with the rays of +the sun. On the contrary, it is easily demonstrated, as Pasteur first +proved, that the lowest fungi, devoid of chlorophyll, or of any +substitute for it, as they are, nevertheless possess the characteristic +manufacturing powers of plants in a very high degree. Only it is +necessary that they should be supplied with a different kind of raw +material; as they cannot extract carbon from carbonic acid, they must be +furnished with something else that contains carbon. Tartaric acid is such +a substance; and if a single spore of the commonest and most troublesome +of moulds--_Penicillium_--be sown in a saucerful of water, in which +tartrate of ammonia, with a small percentage of phosphates and sulphates +is contained, and kept warm, whether in the dark or exposed to light, it +will, in a short time, give rise to a thick crust of mould, which +contains many million times the weight of the original spore, in protein +compounds and cellulose. Thus we have a very wide basis of fact for the +generalisation that plants are essentially characterised by their +manufacturing capacity--by their power of working up mere mineral matters +into complex organic compounds. + +Contrariwise, there is a no less wide foundation for the generalisation +that animals, as Cuvier puts it, depend directly or indirectly upon +plants for the materials of their bodies; that is, either they are +herbivorous, or they eat other animals which are herbivorous. + +But for what constituents of their bodies are animals thus dependent upon +plants? Certainly not for their horny matter; nor for chondrin, the +proximate chemical element of cartilage; nor for gelatine; nor for +syntonin, the constituent of muscle; nor for their nervous or biliary +substances; nor for their amyloid matters; nor, necessarily, for their +fats. + +It can be experimentally demonstrated that animals can make these for +themselves. But that which they cannot make, but must, in all known +cases, obtain directly or indirectly from plants, is the peculiar +nitrogenous matter, protein. Thus the plant is the ideal _prolétaire_ of +the living world, the worker who produces; the animal, the ideal +aristocrat, who mostly occupies himself in consuming, after the manner of +that noble representative of the line of Zähdarm, whose epitaph is +written in "Sartor Resartus." + +Here is our last hope of finding a sharp line of demarcation between +plants and animals; for, as I have already hinted, there is a border +territory between the two kingdoms, a sort of no-man's-land, the +inhabitants of which certainly cannot be discriminated and brought to +their proper allegiance in any other way. + +Some months ago, Professor Tyndall asked me to examine a drop of infusion +of hay, placed under an excellent and powerful microscope, and to tell +him what I thought some organisms visible in it were. I looked and +observed, in the first place, multitudes of _Bacteria_ moving about with +their ordinary intermittent spasmodic wriggles. As to the vegetable +nature of these there is now no doubt. Not only does the close +resemblance of the _Bacteria_ to unquestionable plants, such as the +_Oscillatorioe_ and the lower forms of _Fungi_, justify this conclusion, +but the manufacturing test settles the question at once. It is only +needful to add a minute drop of fluid containing _Bacteria_, to water in +which tartrate, phosphate, and sulphate of ammonia are dissolved; and, in +a very short space of time, the clear fluid becomes milky by reason of +their prodigious multiplication, which, of course, implies the +manufacture of living Bacterium-stuff out of these merely saline matters. + +But other active organisms, very much larger than the _Bacteria_, +attaining in fact the comparatively gigantic dimensions of 1/3000 of an +inch or more, incessantly crossed the field of view. Each of these had a +body shaped like a pear, the small end being slightly incurved and +produced into a long curved filament, or _cilium_, of extreme tenuity. +Behind this, from the concave side of the incurvation, proceeded another +long cilium, so delicate as to be discernible only by the use of the +highest powers and careful management of the light. In the centre of the +pear-shaped body a clear round space could occasionally be discerned, but +not always; and careful watching showed that this clear vacuity appeared +gradually, and then shut up and disappeared suddenly, at regular +intervals. Such a structure is of common occurrence among the lowest +plants and animals, and is known as a _contractile vacuole_. + +The little creature thus described sometimes propelled itself with great +activity, with a curious rolling motion, by the lashing of the front +cilium, while the second cilium trailed behind; sometimes it anchored +itself by the hinder cilium and was spun round by the working of the +other, its motions resembling those of an anchor buoy in a heavy sea. +Sometimes, when two were in full career towards one another, each would +appear dexterously to get out of the other's way; sometimes a crowd would +assemble and jostle one another, with as much semblance of individual +effort as a spectator on the Grands Mulets might observe with a telescope +among the specks representing men in the valley of Chamounix. + +The spectacle, though always surprising, was not new to me. So my reply +to the question put to me was, that these organisms were what biologists +call _Monads_, and though they might be animals, it was also possible +that they might, like the _Bacteria_, be plants. My friend received my +verdict with an expression which showed a sad want of respect for +authority. He would as soon believe that a sheep was a plant. Naturally +piqued by this want of faith, I have thought a good deal over the matter; +and, as I still rest in the lame conclusion I originally expressed, and +must even now confess that I cannot certainly say whether this creature +is an animal or a plant, I think it may be well to state the grounds of +my hesitation at length. But, in the first place, in order that I may +conveniently distinguish this "Monad" from the multitude of other things +which go by the same designation, I must give it a name of its own. I +think (though, for reasons which need not be stated at present, I am not +quite sure) that it is identical with the species _Monas lens_ as defined +by the eminent French microscopist Dujardin, though his magnifying power +was probably insufficient to enable him to see that it is curiously like +a much larger form of monad which he has named _Heteromita_. I shall, +therefore, call it not _Monas_, but _Heteromita lens_. + +I have been unable to devote to my _Heteromita_ the prolonged study +needful to work out its whole history, which would involve weeks, or it +may be months, of unremitting attention. But I the less regret this +circumstance, as some remarkable observations recently published by +Messrs. Dallinger and Drysdale[5] on certain Monads, relate, in part, to +a form so similar to my _Heteromita lens_, that the history of the one +may be used to illustrate that of the other. These most patient and +painstaking observers, who employed the highest attainable powers of the +microscope and, relieving one another, kept watch day and night over the +same individual monads, have been enabled to trace out the whole history +of their _Heteromita_; which they found in infusions of the heads of +fishes of the Cod tribe. + +[Footnote 5: "Researches in the Life-history of a Cercomonad: a Lesson in +Biogenesis"; and "Further Researches in the Life-history of the Monads," +--_Monthly Microscopical Journal_, 1873.] + +Of the four monads described and figured by these investigators, one, as +I have said, very closely resembles _Heteromita lens_ in every +particular, except that it has a separately distinguishable central +particle or "nucleus," which is not certainly to be made out in +_Heteromita lens_; and that nothing is said by Messrs. Dallinger and +Drysdale of the existence of a contractile vacuole in this monad, though +they describe it in another. + +Their _Heteromita_, however, multiplied rapidly by fission. Sometimes a +transverse constriction appeared; the hinder half developed a new cilium, +and the hinder cilium gradually split from its base to its free end, +until it was divided into two; a process which, considering the fact that +this fine filament cannot be much more than 1/100000 of an inch in +diameter, is wonderful enough. The constriction of the body extended +inwards until the two portions were united by a narrow isthmus; finally, +they separated and each swam away by itself, a complete _Heteromita_, +provided with its two cilia. Sometimes the constriction took a +longitudinal direction, with the same ultimate result. In each case the +process occupied not more than six or seven minutes. At this rate, a +single _Heteromita_ would give rise to a thousand like itself in the +course of an hour, to about a million in two hours, and to a number +greater than the generally assumed number of human beings now living in +the world in three hours; or, if we give each _Heteromita_ an hour's +enjoyment of individual existence, the same result will be obtained in +about a day. The apparent suddenness of the appearance of multitudes of +such organisms as these in any nutritive fluid to which one obtains +access is thus easily explained. + +During these processes of multiplication by fission, the _Heteromita_ +remains active; but sometimes another mode of fission occurs. The body +becomes rounded and quiescent, or nearly so; and, while in this resting +state, divides into two portions, each of which is rapidly converted into +an active _Heteromita_. + +A still more remarkable phenomenon is that kind of multiplication which +is preceded by the union of two monads, by a process which is termed +_conjugation_. Two active _Heteromitoe_ become applied to one another, +and then slowly and gradually coalesce into one body. The two nuclei run +into one; and the mass resulting from the conjugation of the two +_Heteromitoe_, thus fused together, has a triangular form. The two pairs +of cilia are to be seen, for some time, at two of the angles, which +answer to the small ends of the conjoined monads; but they ultimately +vanish, and the twin organism, in which all visible traces of +organisation have disappeared, falls into a state of rest. Sudden wave- +like movements of its substance next occur; and, in a short time, the +apices of the triangular mass burst, and give exit to a dense yellowish, +glairy fluid, filled with minute granules. This process, which, it will +be observed, involves the actual confluence and mixture of the substance +of two distinct organisms, is effected in the space of about two hours. + +The authors whom I quote say that they "cannot express" the excessive +minuteness of the granules in question, and they estimate their diameter +at less than 1/200000 of an inch. Under the highest powers of the +microscope, at present applicable, such specks are hardly discernible. +Nevertheless, particles of this size are massive when compared to +physical molecules; whence there is no reason to doubt that each, small +as it is, may have a molecular structure sufficiently complex to give +rise to the phenomena of life. And, as a matter of fact, by patient +watching of the place at which these infinitesimal living particles were +discharged, our observers assured themselves of their growth and +development into new monads. In about four hours from their being set +free, they had attained a sixth of the length of the parent, with the +characteristic cilia, though at first they were quite motionless; and, in +four hours more, they had attained the dimensions and exhibited all the +activity of the adult. These inconceivably minute particles are therefore +the germs of the _Heteromita_; and from the dimensions of these germs it +is easily shown that the body formed by conjugation may, at a low +estimate, have given exit to thirty thousand of them; a result of a +matrimonial process whereby the contracting parties, without a metaphor, +"become one flesh," enough to make a Malthusian despair of the future of +the Universe. + +I am not aware that the investigators from whom I have borrowed this +history have endeavoured to ascertain whether their monads take solid +nutriment or not; so that though they help us very much to fill up the +blanks in the history of my _Heteromita_, their observations throw no +light on the problem we are trying to solve--Is it an animal or is it a +plant? + +Undoubtedly it is possible to bring forward very strong arguments in +favour of regarding _Heteromita_ as a plant. + +For example, there is a Fungus, an obscure and almost microscopic mould, +termed _Peronospora infestans_. Like many other Fungi, the _Peronosporoe_ +are parasitic upon other plants; and this particular _Peronospora_ +happens to have attained much notoriety and political importance, in a +way not without a parallel in the career of notorious politicians, +namely, by reason of the frightful mischief it has done to mankind. For +it is this _Fungus_ which is the cause of the potato disease; and, +therefore, _Peronospora infestans_ (doubtless of exclusively Saxon +origin, though not accurately known to be so) brought about the Irish +famine. The plants afflicted with the malady are found to be infested by +a mould, consisting of fine tubular filaments, termed _hyphoe_, which +burrow through the substance of the potato plant, and appropriate to +themselves the substance of their host; while, at the same time, directly +or indirectly, they set up chemical changes by which even its woody +framework becomes blackened, sodden, and withered. + +In structure, however, the _Peronospora_ is as much a mould as the common +_Penicillium_; and just as the _Penicillium_ multiplies by the breaking +up of its hyphoe into separate rounded bodies, the spores; so, in the +_Peronospora_, certain of the hyphoe grow out into the air through the +interstices of the superficial cells of the potato plant, and develop +spores. Each of these hyphoe usually gives off several branches. The ends +of the branches dilate and become closed sacs, which eventually drop off +as spores. The spores falling on some part of the same potato plant, or +carried by the wind to another, may at once germinate, throwing out +tubular prolongations which become hyphoe, and burrow into the substance +of the plant attacked. But, more commonly, the contents of the spore +divide into six or eight separate portions. The coat of the spore gives +way, and each portion then emerges as an independent organism, which has +the shape of a bean, rather narrower at one end than the other, convex on +one side, and depressed or concave on the opposite. From the depression, +two long and delicate cilia proceed, one shorter than the other, and +directed forwards. Close to the origin of these cilia, in the substance +of the body, is a regularly pulsating, contractile vacuole. The shorter +cilium vibrates actively, and effects the locomotion of the organism, +while the other trails behind; the whole body rolling on its axis with +its pointed end forwards. + +The eminent botanist, De Bary, who was not thinking of our problem, tells +us, in describing the movements of these "Zoospores," that, as they swim +about, "Foreign bodies are carefully avoided, and the whole movement has +a deceptive likeness to the voluntary changes of place which are observed +in microscopic animals." + +After swarming about in this way in the moisture on the surface of a leaf +or stem (which, film though it may be, is an ocean to such a fish) for +half an hour, more or less, the movement of the zoospore becomes slower, +and is limited to a slow turning upon its axis, without change of place. +It then becomes quite quiet, the cilia disappear, it assumes a spherical +form, and surrounds itself with a distinct, though delicate, membranous +coat. A protuberance then grows out from one side of the sphere, and +rapidly increasing in length, assumes the character of a hypha. The +latter penetrates into the substance of the potato plant, either by +entering a stomate, or by boring through the wall of an epidermic cell, +and ramifies, as a mycelium, in the substance of the plant, destroying +the tissues with which it comes in contact. As these processes of +multiplication take place very rapidly, millions of spores are soon set +free from a single infested plant; and, from their minuteness, they are +readily transported by the gentlest breeze. Since, again, the zoospores +set free from each spore, in virtue of their powers of locomotion, +swiftly disperse themselves over the surface, it is no wonder that the +infection, once started, soon spreads from field to field, and extends +its ravages over a whole country. + +However, it does not enter into my present plan to treat of the potato +disease, instructively as its history bears upon that of other epidemics; +and I have selected the case of the _Peroganspora_ simply because it +affords an example of an organism, which, in one stage of its existence, +is truly a "Monad," indistinguishable by any important character from our +_Heteromita_, and extraordinarily like it in some respects. And yet this +"Monad" can be traced, step by step, through the series of metamorphoses +which I have described, until it assumes the features of an organism, +which is as much a plant as is an oak or an elm. + +Moreover, it would be possible to pursue the analogy farther. Under +certain circumstances, a process of conjugation takes place in the +_Peronospora_. Two separate portions of its protoplasm become fused +together, surround themselves with a thick coat and give rise to a sort +of vegetable egg called an _oospore_. After a period of rest, the +contents of the oospore break up into a number of zoospores like those +already described, each of which, after a period of activity, germinates +in the ordinary way. This process obviously corresponds with the +conjugation and subsequent setting free of germs in the _Heteromita_. + +But it may be said that the _Peronospora_ is, after all, a questionable +sort of plant; that it seems to be wanting in the manufacturing power, +selected as the main distinctive character of vegetable life; or, at any +rate, that there is no proof that it does not get its protein matter +ready made from the potato plant. + +Let us, therefore, take a case which is not open to these objections. + +There are some small plants known to botanists as members of the genus +_Colcochaete_, which, without being truly parasitic, grow upon certain +water-weeds, as lichens grow upon trees. The little plant has the form of +an elegant green star, the branching arms of which are divided into +cells. Its greenness is due to its chlorophyll, and it undoubtedly has +the manufacturing power in full degree, decomposing carbonic acid and +setting oxygen free, under the influence of sunlight. But the +protoplasmic contents of some of the cells of which the plant is made up +occasionally divide, by a method similar to that which effects the +division of the contents of the _Peronospora_ spore; and the severed +portions are then set free as active monad-like zoospores. Each is oval +and is provided at one extremity with two long active cilia. Propelled by +these, it swims about for a longer or shorter time, but at length comes +to a state of rest and gradually grows into a _Coleochaete_. Moreover, as +in the _Peronospora_, conjugation may take place and result in an +oospore; the contents of which divide and are set free as monadiform +germs. + +If the whole history of the zoospores of _Peronospora_ and of +_Coleochaete_ were unknown, they would undoubtedly be classed among +"Monads" with the same right as _Heteromita_; why then may not +_Heteromita_ be a plant, even though the cycle of forms through which it +passes shows no terms quite so complex as those which occur in +_Peronospora_ and _Coleochaete_? And, in fact, there are some green +organisms, in every respect characteristically plants, such as +_Chlamydomonas_, and the common _Volvox_, or so-called "Globe +animalcule," which run through a cycle of forms of just the same simple +character as those of _Heteromita_. + +The name of _Chlamydomonas_ is applied to certain microscopic green +bodies, each of which consists of a protoplasmic central substance +invested by a structureless sac. The latter contains cellulose, as in +ordinary plants; and the chlorophyll which gives the green colour enables +the _Chlamydomonas_ to decompose carbonic acid and fix carbon as they do. +Two long cilia protrude through the cell-wall, and effect the rapid +locomotion of this "monad," which, in all respects except its mobility, +is characteristically a plant. Under ordinary circumstances, the +_Chlamydomonas_ multiplies by simple fission, each splitting into two or +into four parts, which separate and become independent organisms. +Sometimes, however, the _Chlamydomonas_ divides into eight parts, each of +which is provided with four instead of two cilia. These "zoospores" +conjugate in pairs, and give rise to quiescent bodies, which multiply by +division, find eventually pass into the active state. + +Thus, so far as outward form and the general character of the cycle of +modifications, through which the organism passes in the course of its +life, are concerned, the resemblance between _Chlamydomonas_ and +_Heteromita_ is of the closest description. And on the face of the matter +there is no ground for refusing to admit that _Heteromita_ may be related +to _Chlamydomonas_, as the colourless fungus is to the green alga. +_Volvox_ may be compared to a hollow sphere, the wall of which is made up +of coherent Chlamydomonads; and which progresses with a rotating motion +effected by the paddling of the multitudinous pairs of cilia which +project from its surface. Each _Volvox_-monad, moreover, possesses a red +pigment spot, like the simplest form of eye known among animals. The +methods of fissive multiplication and of conjugation observed in the +monads of this locomotive globe are essentially similar to those observed +in _Chlamydomonas_; and, though a hard battle has been fought over it, +_Volvox_ is now finally surrendered to the Botanists. + +Thus there is really no reason why _Heteromita_ may not be a plant; and +this conclusion would be very satisfactory, if it were not equally easy +to show that there is really no reason why it should not be an animal. +For there are numerous organisms presenting the closest resemblance to +_Heteromita_, and, like it, grouped under the general name of "Monads," +which, nevertheless, can be observed to take in solid nutriment, and +which, therefore, have a virtual, if not an actual, mouth and digestive +cavity, and thus come under Cuvier's definition of an animal. Numerous +forms of such animals have been described by Ehrenberg, Dujardin, H. +James Clark, and other writers on the _Infusoria_. Indeed, in another +infusion of hay in which my _Heteromita lens_ occurred, there were +innumerable such infusorial animalcules belonging to the well-known +species _Colpoda cucullus_.[6] + +[Footnote 6: Excellently described by Stein, almost all of whose +statements I have verified.] + +Full-sized specimens of this animalcule attain a length of between 1/300 +or 1/400 of an inch, so that it may have ten times the length and a +thousand times the mass of a _Heteromita_. In shape, it is not altogether +unlike _Heteromita_. The small end, however, is not produced into one +long cilium, but the general surface of the body is covered with small +actively vibrating ciliary organs, which are only longest at the small +end. At the point which answers to that from which the two cilia arise in +_Heteromita_, there is a conical depression, the mouth; and, in young +specimens, a tapering filament, which reminds one of the posterior cilium +of _Heteromita_, projects from this region. + +The body consists of a soft granular protoplasmic substance, the middle +of which is occupied by a large oval mass called the "nucleus"; while, at +its hinder end, is a "contractile vacuole," conspicuous by its regular +rhythmic appearances and disappearances. Obviously, although the +_Colpoda_ is not a monad, it differs from one only in subordinate +details. Moreover, under certain conditions, it becomes quiescent, +incloses itself in a delicate case or _cyst_, and then divides into two, +four, or more portions, which are eventually set free and swim about as +active _Colpodoe_. + +But this creature is an unmistakable animal, and full-sized _Colpodoe_ +may be fed as easily as one feeds chickens. It is only needful to diffuse +very finely ground carmine through the water in which they live, and, in +a very short time, the bodies of the _Colpodoe_ are stuffed with the +deeply-coloured granules of the pigment. + +And if this were not sufficient evidence of the animality of _Colpoda_, +there comes the fact that it is even more similar to another well-known +animalcule, _Paramoecium_, than it is to a monad. But _Paramoecium_ is so +huge a creature compared with those hitherto discussed--it reaches 1/120 +of an inch or more in length--that there is no difficulty in making out +its organisation in detail; and in proving that it is not only an animal, +but that it is an animal which possesses a somewhat complicated +organisation. For example, the surface layer of its body is different in +structure from the deeper parts. There are two contractile vacuoles, from +each of which radiates a system of vessel-like canals; and not only is +there a conical depression continuous with a tube, which serve as mouth +and gullet, but the food ingested takes a definite course, and refuse is +rejected from a definite region. Nothing is easier than to feed these +animals, and to watch the particles of indigo or carmine accumulate at +the lower end of the gullet. From this they gradually project, surrounded +by a ball of water, which at length passes with a jerk, oddly simulating +a gulp, into the pulpy central substance of the body, there to circulate +up one side and down the other, until its contents are digested and +assimilated. Nevertheless, this complex animal multiplies by division, as +the monad does, and, like the monad, undergoes conjugation. It stands in +the same relation to _Heteromita_ on the animal side, as _Coleochaete_ +does on the plant side. Start from either, and such an insensible series +of gradations leads to the monad that it is impossible to say at any +stage of the progress where the line between the animal and the plant +must be drawn. + +There is reason to think that certain organisms which pass through a +monad stage of existence, such as the _Myxomycetes_, are, at one time of +their lives, dependent upon external sources for their protein matter, or +are animals; and, at another period, manufacture it, or are plants. And +seeing that the whole progress of modern investigation is in favour of +the doctrine of continuity, it is a fair and probable speculation--though +only a speculation--that, as there are some plants which can manufacture +protein out of such apparently intractable mineral matters as carbonic +acid, water, nitrate of ammonia, metallic and earthy salts; while others +need to be supplied with their carbon and nitrogen in the somewhat less +raw form of tartrate of ammonia and allied compounds; so there may be yet +others, as is possibly the case with the true parasitic plants, which can +only manage to put together materials still better prepared--still more +nearly approximated to protein--until we arrive at such organisms as the +_Psorospermioe_ and the _Panhistophyton_, which are as much animal as +vegetable in structure, but are animal in their dependence on other +organisms for their food. + +The singular circumstance observed by Meyer, that the _Torula_ of yeast, +though an indubitable plant, still flourishes most vigorously when +supplied with the complex nitrogenous substance, pepsin; the probability +that the _Peronospora_ is nourished directly by the protoplasm of the +potato-plant; and the wonderful facts which have recently been brought to +light respecting insectivorous plants, all favour this view; and tend to +the conclusion that the difference between animal and plant is one of +degree rather than of kind, and that the problem whether, in a given +case, an organism is an animal or a plant, may be essentially insoluble. + + + +VII + + +A LOBSTER; OR, THE STUDY OF ZOOLOGY + +[1861] + +Natural history is the name familiarly applied to the study of the +properties of such natural bodies as minerals, plants, and animals; the +sciences which embody the knowledge man has acquired upon these subjects +are commonly termed Natural Sciences, in contradistinction to other so- +called "physical" sciences; and those who devote themselves especially to +the pursuit of such sciences have been and are commonly termed +"Naturalists." + +Linnaeus was a naturalist in this wide sense, and his "Systema Naturae" was +a work upon natural history, in the broadest acceptation of the term; in +it, that great methodising spirit embodied all that was known in his time +of the distinctive characters of minerals, animals, and plants. But the +enormous stimulus which Linnaeus gave to the investigation of nature soon +rendered it impossible that any one man should write another "Systema +Naturae," and extremely difficult for any one to become even a naturalist +such as Linnaeus was. + +Great as have been the advances made by all the three branches of +science, of old included under the title of natural history, there can be +no doubt that zoology and botany have grown in an enormously greater +ratio than mineralogy; and hence, as I suppose, the name of "natural +history" has gradually become more and more definitely attached to these +prominent divisions of the subject, and by "naturalist" people have meant +more and more distinctly to imply a student of the structure and function +of living beings. + +However this may be, it is certain that the advance of knowledge has +gradually widened the distance between mineralogy and its old associates, +while it has drawn zoology and botany closer together; so that of late +years it has been found convenient (and indeed necessary) to associate +the sciences which deal with vitality and all its phenomena under the +common head of "biology"; and the biologists have come to repudiate any +blood-relationship with their foster-brothers, the mineralogists. + +Certain broad laws have a general application throughout both the animal +and the vegetable worlds, but the ground common to these kingdoms of +nature is not of very wide extent, and the multiplicity of details is so +great, that the student of living beings finds himself obliged to devote +his attention exclusively either to the one or the other. If he elects to +study plants, under any aspect, we know at once what to call him. He is a +botanist, and his science is botany. But if the investigation of animal +life be his choice, the name generally applied to him will vary according +to the kind of animals he studies, or the particular phenomena of animal +life to which he confines his attention. If the study of man is his +object, he is called an anatomist, or a physiologist, or an ethnologist; +but if he dissects animals, or examines into the mode in which their +functions are performed, he is a comparative anatomist or comparative +physiologist. If he turns his attention to fossil animals, he is a +palaeontologist. If his mind is more particularly directed to the specific +description, discrimination, classification, and distribution of animals, +he is termed a zoologist. + +For the purpose of the present discourse, however, I shall recognise none +of these titles save the last, which I shall employ as the equivalent of +botanist, and I shall use the term zoology is denoting the whole doctrine +of animal life, in contradistinction to botany, which signifies the whole +doctrine of vegetable life. + +Employed in this sense, zoology, like botany, is divisible into three +great but subordinate sciences, morphology, physiology, and distribution, +each of which may, to a very great extent, be studied independently of +the other. + +Zoological morphology is the doctrine of animal form or structure. +Anatomy is one of its branches; development is another; while +classification is the expression of the relations which different animals +bear to one another, in respect of their anatomy and their development. + +Zoological distribution is the study of animals in relation to the +terrestrial conditions which obtain now, or have obtained at any previous +epoch of the earth's history. + +Zoological physiology, lastly, is the doctrine of the functions or +actions of animals. It regards animal bodies as machines impelled by +certain forces, and performing an amount of work which can be expressed +in terms of the ordinary forces of nature. The final object of physiology +is to deduce the facts of morphology, on the one hand, and those of +distribution on the other, from the laws of the molecular forces of +matter. + +Such is the scope of zoology. But if I were to content myself with the +enunciation of these dry definitions, I should ill exemplify that method +of teaching this branch of physical science, which it is my chief +business to-night to recommend. Let us turn away then from abstract +definitions. Let us take some concrete living thing, some animal, the +commoner the better, and let us see how the application of common sense +and common logic to the obvious facts it presents, inevitably leads us +into all these branches of zoological science. + +I have before me a lobster. When I examine it, what appears to be the +most striking character it presents? Why, I observe that this part which +we call the tail of the lobster, is made up of six distinct hard rings +and a seventh terminal piece. If I separate one of the middle rings, say +the third, I find it carries upon its under surface a pair of limbs or +appendages, each of which consists of a stalk and two terminal pieces. So +that I can represent a transverse section of the ring and its appendages +upon the diagram board in this way. + +If I now take the fourth ring, I find it has the same structure, and so +have the fifth and the second; so that, in each of these divisions of the +tail, I find parts which correspond with one another, a ring and two +appendages; and in each appendage a stalk and two end pieces. These +corresponding parts are called, in the technical language of anatomy, +"homologous parts." The ring of the third division is the "homologue" of +the ring of the fifth, the appendage of the former is the homologue of +the appendage of the latter. And, as each division exhibits corresponding +parts in corresponding places, we say that all the divisions are +constructed upon the same plan. But now let us consider the sixth +division. It is similar to, and yet different from, the others. The ring +is essentially the same as in the other divisions; but the appendages +look at first as if they were very different; and yet when we regard them +closely, what do we find? A stalk and two terminal divisions, exactly as +in the others, but the stalk is very short and very thick, the terminal +divisions are very broad and flat, and one of them is divided into two +pieces. + +I may say, therefore, that the sixth segment is like the others in plan, +but that it is modified in its details. + +The first segment is like the others, so far as its ring is concerned, +and though its appendages differ from any of those yet examined in the +simplicity of their structure, parts corresponding with the stem and one +of the divisions of the appendages of the other segments can be readily +discerned in them. + +Thus it appears that the lobster's tail is composed of a series of +segments which are fundamentally similar, though each presents peculiar +modifications of the plan common to all. But when I turn to the forepart +of the body I see, at first, nothing but a great shield-like shell, +called technically the "carapace," ending in front in a sharp spine, on +either side of which are the curious compound eyes, set upon the ends of +stout movable stalks. Behind these, on the under side of the body, are +two pairs of long feelers, or antennae, followed by six pairs of jaws +folded against one another over the mouth, and five pairs of legs, the +foremost of these being the great pinchers, or claws, of the lobster. + +It looks, at first, a little hopeless to attempt to find in this complex +mass a series of rings, each with its pair of appendages, such as I have +shown you in the abdomen, and yet it is not difficult to demonstrate +their existence. Strip off the legs, and you will find that each pair is +attached to a very definite segment of the under wall of the body; but +these segments, instead of being the lower parts of free rings, as in the +tail, are such parts of rings which are all solidly united and bound +together; and the like is true of the jaws, the feelers, and the eye- +stalks, every pair of which is borne upon its own special segment. Thus +the conclusion is gradually forced upon us, that the body of the lobster +is composed of as many rings as there are pairs of appendages, namely, +twenty in all, but that the six hindmost rings remain free and movable, +while the fourteen front rings become firmly soldered together, their +backs forming one continuous shield--the carapace. + +Unity of plan, diversity in execution, is the lesson taught by the study +of the rings of the body, and the same instruction is given still more +emphatically by the appendages. If I examine the outermost jaw I find it +consists of three distinct portions, an inner, a middle, and an outer, +mounted upon a common stem; and if I compare this jaw with the legs +behind it, or the jaws in front of it, I find it quite easy to see, that, +in the legs, it is the part of the appendage which corresponds with the +inner division, which becomes modified into what we know familiarly as +the "leg," while the middle division disappears, and the outer division +is hidden under the carapace. Nor is it more difficult to discern that, +in the appendages of the tail, the middle division appears again and the +outer vanishes; while, on the other hand, in the foremost jaw, the so- +called mandible, the inner division only is left; and, in the same way, +the parts of the feelers and of the eye-stalks can be identified with +those of the legs and jaws. + +But whither does all this tend? To the very remarkable conclusion that a +unity of plan, of the same kind as that discoverable in the tail or +abdomen of the lobster, pervades the whole organisation of its skeleton, +so that I can return to the diagram representing any one of the rings of +the tail, which I drew upon the board, and by adding a third division to +each appendage, I can use it as a sort of scheme or plan of any ring of +the body. I can give names to all the parts of that figure, and then if I +take any segment of the body of the lobster, I can point out to you +exactly, what modification the general plan has undergone in that +particular segment; what part has remained movable, and what has become +fixed to another; what has been excessively developed and metamorphosed +and what has been suppressed. + +But I imagine I hear the question, How is all this to be tested? No doubt +it is a pretty and ingenious way of looking at the structure of any +animal; but is it anything more? Does Nature acknowledge, in any deeper +way, this unity of plan we seem to trace? + +The objection suggested by these questions is a very valid and important +one, and morphology was in an unsound state so long as it rested upon the +mere perception of the analogies which obtain between fully formed parts. +The unchecked ingenuity of speculative anatomists proved itself fully +competent to spin any number of contradictory hypotheses out of the same +facts, and endless morphological dreams threatened to supplant scientific +theory. + +Happily, however, there is a criterion of morphological truth, and a sure +test of all homologies. Our lobster has not always been what we see it; +it was once an egg, a semifluid mass of yolk, not so big as a pin's head, +contained in a transparent membrane, and exhibiting not the least trace +of any one of those organs, the multiplicity and complexity of which, in +the adult, are so surprising. After a time, a delicate patch of cellular +membrane appeared upon one face of this yolk, and that patch was the +foundation of the whole creature, the clay out of which it would be +moulded. Gradually investing the yolk, it became subdivided by transverse +constrictions into segments, the forerunners of the rings of the body. +Upon the ventral surface of each of the rings thus sketched out, a pair +of bud-like prominences made their appearance--the rudiments of the +appendages of the ring. At first, all the appendages were alike, but, as +they grew, most of them became distinguished into a stem and two terminal +divisions, to which, in the middle part of the body, was added a third +outer division; and it was only at a later period, that by the +modification, or absorption, of certain of these primitive constituents, +the limbs acquired their perfect form. + +Thus the study of development proves that the doctrine of unity of plan +is not merely a fancy, that it is not merely one way of looking at the +matter, but that it is the expression of deep-seated natural facts. The +legs and jaws of the lobster may not merely be regarded as modifications +of a common type,--in fact and in nature they are so,--the leg and the +jaw of the young animal being, at first, indistinguishable. + +These are wonderful truths, the more so because the zoologist finds them +to be of universal application. The investigation of a polype, of a +snail, of a fish, of a horse, or of a man, would have led us, though by a +less easy path, perhaps, to exactly the same point. Unity of plan +everywhere lies hidden under the mask of diversity of structure--the +complex is everywhere evolved out of the simple. Every animal has at +first the form of an egg, and every animal and every organic part, in +reaching its adult state, passes through conditions common to other +animals and other adult parts; and this leads me to another point. I have +hitherto spoken as if the lobster were alone in the world, but, as I need +hardly remind you, there are myriads of other animal organisms. Of these, +some, such as men, horses, birds, fishes, snails, slugs, oysters, corals, +and sponges, are not in the least like the lobster. But other animals, +though they may differ a good deal from the lobster, are yet either very +like it, or are like something that is like it. The cray fish, the rock +lobster, and the prawn, and the shrimp, for example, however different, +are yet so like lobsters, that a child would group them as of the lobster +kind, in contradistinction to snails and slugs; and these last again +would form a kind by themselves, in contradistinction to cows, horses, +and sheep, the cattle kind. + +But this spontaneous grouping into "kinds" is the first essay of the +human mind at classification, or the calling by a common name of those +things that are alike, and the arranging them in such a manner as best to +suggest the sum of their likenesses and unlikenesses to other things. + +Those kinds which include no other subdivisions than the sexes, or +various breeds, are called, in technical language, species. The English +lobster is a species, our cray fish is another, our prawn is another. In +other countries, however, there are lobsters, cray fish, and prawns, very +like ours, and yet presenting sufficient differences to deserve +distinction. Naturalists, therefore, express this resemblance and this +diversity by grouping them as distinct species of the same "genus." But +the lobster and the cray fish, though belonging to distinct genera, have +many features in common, and hence are grouped together in an assemblage +which is called a family. More distant resemblances connect the lobster +with the prawn and the crab, which are expressed by putting all these +into the same order. Again, more remote, but still very definite, +resemblances unite the lobster with the woodlouse, the king crab, the +water flea, and the barnacle, and separate them from all other animals; +whence they collectively constitute the larger group, or class, +_Crustacea_. But the _Crustacea_ exhibit many peculiar features in common +with insects, spiders, and centipedes, so that these are grouped into the +still larger assemblage or "province" _Articulata_; and, finally, the +relations which these have to worms and other lower animals, are +expressed by combining the whole vast aggregate into the sub-kingdom of +_Annulosa_. + +If I had worked my way from a sponge instead of a lobster, I should have +found it associated, by like ties, with a great number of other animals +into the sub-kingdom _Protozoa_; if I had selected a fresh-water polype +or a coral, the members of what naturalists term the sub-kingdom +_Coelenterata_, would have grouped themselves around my type; had a snail +been chosen, the inhabitants of all univalve and bivalve, land and water, +shells, the lamp shells, the squids, and the sea-mat would have gradually +linked themselves on to it as members of the same sub-kingdom of +_Mollusca_; and finally, starting from man, I should have been compelled +to admit first, the ape, the rat, the horse, the dog, into the same +class; and then the bird, the crocodile, the turtle, the frog, and the +fish, into the same sub-kingdom of _Vertebrata_. + +And if I had followed out all these various lines of classification +fully, I should discover in the end that there was no animal, either +recent or fossil, which did not at once fall into one or other of these +sub-kingdoms. In other words, every animal is organised upon one or other +of the five, or more, plans, the existence of which renders our +classification possible. And so definitely and precisely marked is the +structure of each animal, that, in the present state of our knowledge, +there is not the least evidence to prove that a form, in the slightest +degree transitional between any of the two groups _Vertebrata, Annulosa, +Mollusca_, and _Coelenterata_, either exists, or has existed, during that +period of the earth's history which is recorded by the geologist.[1] +Nevertheless, you must not for a moment suppose, because no such +transitional forms are known, that the members of the sub-kingdoms are +disconnected from, or independent of, one another. On the contrary, in +their earliest condition they are all similar, and the primordial germs +of a man, a dog, a bird, a fish, a beetle, a snail, and a polype are, in +no essential structural respects, distinguishable. + +[Footnote 1: The different grouping necessitated by later knowledge does +not affect the principle of the argument.--1894.] + +In this broad sense, it may with truth be said, that all living animals, +and all those dead faunae which geology reveals, are bound together by an +all-pervading unity of organisation, of the same character, though not +equal in degree, to that which enables us to discern one and the same +plan amidst the twenty different segments of a lobster's body. Truly it +has been said, that to a clear eye the smallest fact is a window through +which the Infinite may be seen. + +Turning from these purely morphological considerations, let us now +examine into the manner in which the attentive study of the lobster +impels us into other lines of research. + +Lobsters are found in all the European seas; but on the opposite shores +of the Atlantic and in the seas of the southern hemisphere they do not +exist. They are, however, represented in these regions by very closely +allied, but distinct forms--the _Homarus Americanus_ and the _Homarus +Capensis:_ so that we may say that the European has one species of +_Homuarus_; the American, another; the African, another; and thus the +remarkable facts of geographical distribution begin to dawn upon us. + +Again, if we examine the contents of the earth's crust, we shall find in +the latter of those deposits, which have served as the great burying +grounds of past ages, numberless lobster-like animals, but none so +similar to our living lobster as to make zoologists sure that they +belonged even to the same genus. If we go still further back in time, we +discover, in the oldest rocks of all, the remains of animals, constructed +on the same general plan as the lobster, and belonging to the same great +group of _Crustacea_; but for the most part totally different from the +lobster, and indeed from any other living form of crustacean; and thus we +gain a notion of that successive change of the animal population of the +globe, in past ages, which is the most striking fact revealed by geology. + +Consider, now, where our inquiries have led us. We studied our type +morphologically, when we determined its anatomy and its development, and +when comparing it, in these respects, with other animals, we made out its +place in a system of classification. If we were to examine every animal +in a similar manner, we should establish a complete body of zoological +morphology. + +Again, we investigated the distribution of our type in space and in time, +and, if the like had been done with every animal, the sciences of +geographical and geological distribution would have attained their limit. + +But you will observe one remarkable circumstance, that, up to this point, +the question of the life of these organisms has not come under +consideration. Morphology and distribution might be studied almost as +well, if animals and plants were a peculiar kind of crystals, and +possessed none of those functions which distinguish living beings so +remarkably. But the facts of morphology and distribution have to be +accounted for, and the science, the aim of which it is to account for +them, is Physiology. + +Let us return to our lobster once more. If we watched the creature in its +native element, we should see it climbing actively the submerged rocks, +among which it delights to live, by means of its strong legs; or swimming +by powerful strokes of its great tail, the appendages of the sixth joint +of which are spread out into a broad fan-like Propeller: seize it, and it +will show you that its great claws are no mean weapons of offence; +suspend a piece of carrion among its haunts, and it will greedily devour +it, tearing and crushing the flesh by means of its multitudinous jaws. + +Suppose that we had known nothing of the lobster but as an inert mass, an +organic crystal, if I may use the phrase, and that we could suddenly see +it exerting all these powers, what wonderful new ideas and new questions +would arise in our minds! The great new question would be, "How does all +this take place?" the chief new idea would be, the idea of adaptation to +purpose,--the notion, that the constituents of animal bodies are not mere +unconnected parts, but organs working together to an end. Let us consider +the tail of the lobster again from this point of view. Morphology has +taught us that it is a series of segments composed of homologous parts, +which undergo various modifications--beneath and through which a common +plan of formation is discernible. But if I look at the same part +physiologically, I see that it is a most beautifully constructed organ of +locomotion, by means of which the animal can swiftly propel itself either +backwards or forwards. + +But how is this remarkable propulsive machine made to perform its +functions? If I were suddenly to kill one of these animals and to take +out all the soft parts, I should find the shell to be perfectly inert, to +have no more power of moving itself than is possessed by the machinery of +a mill when disconnected from its steam-engine or water-wheel. But if I +were to open it, and take out the viscera only, leaving the white flesh, +I should perceive that the lobster could bend and extend its tail as well +as before. If I were to cut off the tail, I should cease to find any +spontaneous motion in it; but on pinching any portion of the flesh, I +should observe that it underwent a very curious change--each fibre +becoming shorter and thicker. By this act of contraction, as it is +termed, the parts to which the ends of the fibre are attached are, of +course, approximated; and according to the relations of their points of +attachment to the centres of motions of the different rings, the bending +or the extension of the tail results. Close observation of the newly- +opened lobster would soon show that all its movements are due to the same +cause--the shortening and thickening of these fleshy fibres, which are +technically called muscles. + +Here, then, is a capital fact. The movements of the lobster are due to +muscular contractility. But why does a muscle contract at one time and +not at another? Why does one whole group of muscles contract when the +lobster wishes to extend his tail, and another group when he desires to +bend it? What is it originates, directs, and controls the motive power? + +Experiment, the great instrument for the ascertainment of truth in +physical science, answers this question for us. In the head of the +lobster there lies a small mass of that peculiar tissue which is known as +nervous substance. Cords of similar matter connect his brain of the +lobster, directly or indirectly, with the muscles. Now, if these +communicating cords are cut, the brain remaining entire, the power of +exerting what we call voluntary motion in the parts below the section is +destroyed; and, on the other hand, if, the cords remaining entire, the +brain mass be destroyed, the same voluntary mobility is equally lost. +Whence the inevitable conclusion is, that the power of originating these +motions resides in the brain and is propagated along the nervous cords. + +In the higher animals the phenomena which attend this transmission have +been investigated, and the exertion of the peculiar energy which resides +in the nerves has been found to be accompanied by a disturbance of the +electrical state of their molecules. + +If we could exactly estimate the signification of this disturbance; if we +could obtain the value of a given exertion of nerve force by determining +the quantity of electricity, or of heat, of which it is the equivalent; +if we could ascertain upon what arrangement, or other condition of the +molecules of matter, the manifestation of the nervous and muscular +energies depends (and doubtless science will some day or other ascertain +these points), physiologists would have attained their ultimate goal in +this direction; they would have determined the relation of the motive +force of animals to the other forms of force found in nature; and if the +same process had been successfully performed for all the operations which +are carried on in, and by, the animal frame, physiology would be perfect, +and the facts of morphology and distribution would be deducible from the +laws which physiologists had established, combined with those determining +the condition of the surrounding universe. + +There is not a fragment of the organism of this humble animal whose study +would not lead us into regions of thought as large as those which I have +briefly opened up to you; but what I have been saying, I trust, has not +only enabled you to form a conception of the scope and purport of +zoology, but has given you an imperfect example of the manner in which, +in my opinion, that science, or indeed any physical science, may be best +taught. The great matter is, to make teaching real and practical, by +fixing the attention of the student on particular facts; but at the same +time it should be rendered broad and comprehensive, by constant reference +to the generalisations of which all particular facts are illustrations. +The lobster has served as a type of the whole animal kingdom, and its +anatomy and physiology have illustrated for us some of the greatest +truths of biology. The student who has once seen for himself the facts +which I have described, has had their relations explained to him, and has +clearly comprehended them, has, so far, a knowledge of zoology, which is +real and genuine, however limited it may be, and which is worth more than +all the mere reading knowledge of the science he could ever acquire. His +zoological information is, so far, knowledge and not mere hearsay. + +And if it were nay business to fit you for the certificate in zoological +science granted by this department, I should pursue a course precisely +similar in principle to that which I have taken to-night. I should select +a fresh-water sponge, a fresh-water polype or a _Cyanoea_, a fresh-water +mussel, a lobster, a fowl, as types of the five primary divisions of the +animal kingdom. I should explain their structure very fully, and show how +each illustrated the great principles of zoology. Having gone very +carefully and fully over this ground, I should feel that you had a safe +foundation, and I should then take you in the same way, but less +minutely, over similarly selected illustrative types of the classes; and +then I should direct your attention to the special forms enumerated under +the head of types, in this syllabus, and to the other facts there +mentioned. + +That would, speaking generally, be my plan. But I have undertaken to +explain to you the best mode of acquiring and communicating a knowledge +of zoology, and you may therefore fairly ask me for a more detailed and +precise account of the manner in which I should propose to furnish you +with the information I refer to. + +My own impression is, that the best model for all kinds of training in +physical science is that afforded by the method of teaching anatomy, in +use in the medical schools. This method consists of three elements-- +lectures, demonstrations, and examinations. + +The object of lectures is, in the first place, to awaken the attention +and excite the enthusiasm of the student; and this, I am sure, may be +effected to a far greater extent by the oral discourse and by the +personal influence of a respected teacher than in any other way. +Secondly, lectures have the double use of guiding the student to the +salient points of a subject, and at the same time forcing him to attend +to the whole of it, and not merely to that part which takes his fancy. +And lastly, lectures afford the student the opportunity of seeking +explanations of those difficulties which will, and indeed ought to, arise +in the course of his studies. + +What books shall I read? is a question constantly put by the student to +the teacher. My reply usually is, "None: write your notes out carefully +and fully; strive to understand them thoroughly; come to me for the +explanation of anything you cannot understand; and I would rather you did +not distract your mind by reading." A properly composed course of +lectures ought to contain fully as much matter as a student can +assimilate in the time occupied by its delivery; and the teacher should +always recollect that his business is to feed, and not to cram the +intellect. Indeed, I believe that a student who gains from a course of +lectures the simple habit of concentrating his attention upon a +definitely limited series of facts, until they are thoroughly mastered, +has made a step of immeasurable importance. + +But, however good lectures may be, and however extensive the course of +reading by which they are followed up, they are but accessories to the +great instrument of scientific teaching--demonstration. If I insist +unweariedly, nay fanatically, upon the importance of physical science as +an educational agent, it is because the study of any branch of science, +if properly conducted, appears to me to fill up a void left by all other +means of education. I have the greatest respect and love for literature; +nothing would grieve me more than to see literary training other than a +very prominent branch of education: indeed, I wish that real literary +discipline were far more attended to than it is; but I cannot shut my +eyes to the fact, that there is a vast difference between men who have +had a purely literary, and those who have had a sound scientific, +training. + +Seeking for the cause of this difference, I imagine I can find it in the +fact that, in the world of letters, learning and knowledge are one, and +books are the source of both; whereas in science, as in life, learning +and knowledge are distinct, and the study of things, and not of books, is +the source of the latter. + +All that literature has to bestow may be obtained by reading and by +practical exercise in writing and in speaking; but I do not exaggerate +when I say, that none of the best gifts of science are to be won by these +means. On the contrary, the great benefit which a scientific education +bestows, whether is training or as knowledge, is dependent upon the +extent to which the mind of the student is brought into immediate contact +with facts--upon the degree to which he learns the habit of appealing +directly to Nature, and of acquiring through his senses concrete images +of those properties of things, which are, and always will be, but +approximatively expressed in human language. Our way of looking at +Nature, and of speaking about her, varies from year to year; but a fact +once seen, a relation of cause and effect, once demonstratively +apprehended, are possessions which neither change nor pass away, but, on +the contrary, form fixed centres, about which other truths aggregate by +natural affinity. + +Therefore, the great business of the scientific teacher is, to imprint +the fundamental, irrefragable facts of his science, not only by words +upon the mind, but by sensible impressions upon the eye, and ear, and +touch of the student, in so complete a manner, that every term used, or +law enunciated, should afterwards call up vivid images of the particular +structural, or other, facts which furnished the demonstration of the law, +or the illustration of the term. + +Now this important operation can only be achieved by constant +demonstration, which may take place to a certain imperfect extent during +a lecture, but which ought also to be carried on independently, and which +should be addressed to each individual student, the teacher endeavouring, +not so much to show a thing to the learner, as to make him see it for +himself. + +I am well aware that there are great practical difficulties in the way of +effectual zoological demonstrations. The dissection of animals is not +altogether pleasant, and requires much time; nor is it easy to secure an +adequate supply of the needful specimens. The botanist has here a great +advantage; his specimens are easily obtained, are clean and wholesome, +and can be dissected in a private house as well as anywhere else; and +hence, I believe, the fact, that botany is so much more readily and +better taught than its sister science. But, be it difficult or be it +easy, if zoological science is to be properly studied, demonstration, +and, consequently, dissection, must be had. Without it, no man can have a +really sound knowledge of animal organisation. + +A good deal may be done, however, without actual dissection on the +student's part, by demonstration upon specimens and preparations; and in +all probability it would not be very difficult, were the demand +sufficient, to organise collections of such objects, sufficient for all +the purposes of elementary teaching, at a comparatively cheap rate. Even +without these, much might be effected, if the zoological collections, +which are open to the public, were arranged according to what has been +termed the "typical principle"; that is to say, if the specimens exposed +to public view were so selected that the public could learn something +from them, instead of being, as at present, merely confused by their +multiplicity. For example, the grand ornithological gallery at the +British Museum contains between two and three thousand species of birds, +and sometimes five or six specimens of a species. They are very pretty to +look at, and some of the cases are, indeed, splendid; but I will +undertake to say, that no man but a professed ornithologist has ever +gathered much information from the collection. Certainly, no one of the +tens of thousands of the general public who have walked through that +gallery ever knew more about the essential peculiarities of birds when he +left the gallery than when he entered it. But if, somewhere in that vast +hall, there were a few preparations, exemplifying the leading structural +peculiarities and the mode of development of a common fowl; if the types +of the genera, the leading modifications in the skeleton, in the plumage +at various ages, in the mode of nidification, and the like, among birds, +were displayed; and if the other specimens were put away in a place where +the men of science, to whom they are alone useful, could have free access +to them, I can conceive that this collection might become a great +instrument of scientific education. + +The last implement of the teacher to which I have adverted is +examination--a means of education now so thoroughly understood that I +need hardly enlarge upon it. I hold that both written and oral +examinations are indispensable, and, by requiring the description of +specimens, they may be made to supplement demonstration. + +Such is the fullest reply the time at my disposal will allow me to give +to the question--how may a knowledge of zoology be best acquired and +communicated? + +But there is a previous question which may be moved, and which, in fact, +I know many are inclined to move. It is the question, why should teachers +be encouraged to acquire a knowledge of this, or any other branch of +physical science? What is the use, it is said, of attempting to make +physical science a branch of primary education? Is it not probable that +teachers, in pursuing such studies, will be led astray from the +acquirement of more important but less attractive knowledge? And, even if +they can learn something of science without prejudice to their +usefulness, what is the good of their attempting to instil that knowledge +into boys whose real business is the acquisition of reading, writing, and +arithmetic? + +These questions are, and will be, very commonly asked, for they arise +from that profound ignorance of the value and true position of physical +science, which infests the minds of the most highly educated and +intelligent classes of the community. But if I did not feel well assured +that they are capable of being easily and satisfactorily answered; that +they have been answered over and over again; and that the time will come +when men of liberal education will blush to raise such questions--I +should be ashamed of my position here to-night. Without doubt, it is your +great and very important function to carry out elementary education; +without question, anything that should interfere with the faithful +fulfilment of that duty on your part would be a great evil; and if I +thought that your acquirement of the elements of physical science, and +your communication of those elements to your pupils, involved any sort of +interference with your proper duties, I should be the first person to +protest against your being encouraged to do anything of the kind. + +But is it true that the acquisition of such a knowledge of science as is +proposed, and the communication of that knowledge, are calculated to +weaken your usefulness? Or may I not rather ask, is it possible for you +to discharge your functions properly without these aids? + +What is the purpose of primary intellectual education? I apprehend that +its first object is to train the young in the use of those tools +wherewith men extract knowledge from the ever-shifting succession of +phenomena which pass before their eyes; and that its second object is to +inform them of the fundamental laws which have been found by experience +to govern the course of things, so that they may not be turned out into +the world naked, defenceless, and a prey to the events they might +control. + +A boy is taught to read his own and other languages, in order that he may +have access to infinitely wider stores of knowledge than could ever be +opened to him by oral intercourse with his fellow men; he learns to +write, that his means of communication with the rest of mankind may be +indefinitely enlarged, and that he may record and store up the knowledge +he acquires. He is taught elementary mathematics, that he may understand +all those relations of number and form, upon which the transactions of +men, associated in complicated societies, are built, and that he may have +some practice in deductive reasoning. + +All these operations of reading, writing, and ciphering, are intellectual +tools, whose use should, before all things, be learned, and learned +thoroughly; so that the youth may be enabled to make his life that which +it ought to be, a continual progress in learning and in wisdom. + +But, in addition, primary education endeavours to fit a boy out with a +certain equipment of positive knowledge. He is taught the great laws of +morality; the religion of his sect; so much history and geography as will +tell him where the great countries of the world are, what they are, and +how they have become what they are. + +Without doubt all these are most fitting and excellent things to teach a +boy; I should be very sorry to omit any of them from any scheme of +primary intellectual education. The system is excellent, so far as it +goes. + +But if I regard it closely, a curious reflection arises. I suppose that, +fifteen hundred years ago, the child of any well-to-do Roman citizen was +taught just these same things; reading and writing in his own, and, +perhaps, the Greek tongue; the elements of mathematics; and the religion, +morality, history, and geography current in his time. Furthermore, I do +not think I err in affirming, that, if such a Christian Roman boy, who +had finished his education, could be transplanted into one of our public +schools, and pass through its course of instruction, he would not meet +with a single unfamiliar line of thought; amidst all the new facts he +would have to learn, not one would suggest a different mode of regarding +the universe from that current in his own time. + +And yet surely there is some great difference between the civilisation of +the fourth century and that of the nineteenth, and still more between the +intellectual habits and tone of thought of that day and this? + +And what has made this difference? I answer fearlessly--The prodigious +development of physical science within the last two centuries. + +Modern civilisation rests upon physical science; take away her gifts to +our own country, and our position among the leading nations of the world +is gone to-morrow; for it is physical science only that makes +intelligence and moral energy stronger than brute force. + +The whole of modern thought is steeped in science; it has made its way +into the works of our best poets, and even the mere man of letters, who +affects to ignore and despise science, is unconsciously impregnated with +her spirit, and indebted for his best products to her methods. I believe +that the greatest intellectual revolution mankind has yet seen is now +slowly taking place by her agency. She is teaching the world that the +ultimate court of appeal is observation and experiment, and not +authority; she is teaching it to estimate the value of evidence; she is +creating a firm and living faith in the existence of immutable moral and +physical laws, perfect obedience to which is the highest possible aim of +an intelligent being. + +But of all this your old stereotyped system of education takes no note. +Physical science, its methods, its problems, and its difficulties, will +meet the poorest boy at every turn, and yet we educate him in such a +manner that he shall enter the world as ignorant of the existence of the +methods and facts of science as the day he was born. The modern world is +full of artillery; and we turn out our children to do battle in it, +equipped with the shield and sword of an ancient gladiator. + +Posterity will cry shame on us if we do not remedy this deplorable state +of things. Nay, if we live twenty years longer, our own consciences will +cry shame on us. + +It is my firm conviction that the only way to remedy it is to make the +elements of physical science an integral part of primary education. I +have endeavoured to show you how that may be done for that branch of +science which it is my business to pursue; and I can but add, that I +should look upon the day when every schoolmaster throughout this land was +a centre of genuine, however rudimentary, scientific knowledge, as an +epoch in the history of the country. + +But let me entreat you to remember my last words. Addressing myself to +you, as teachers, I would say, mere book learning in physical science is +a sham and a delusion--what you teach, unless you wish to be impostors, +that you must first know; and real knowledge in science means personal +acquaintance with the facts, be they few or many.[2] + +[Footnote 2: It has been suggested to me that these words may be taken to +imply a discouragement on my part of any sort of scientific instruction +which does not give an acquaintance with the facts at first hand. But +this is not my meaning. The ideal of scientific teaching is, no doubt, a +system by which the scholar sees every fact for himself, and the teacher +supplies only the explanations. Circumstances, however, do not often +allow of the attainment of that ideal, and we must put up with the next +best system--one in which the scholar takes a good deal on trust from a +teacher, who, knowing the facts by his own knowledge, can describe them +with so much vividness as to enable his audience to form competent ideas +concerning them. The system which I repudiate is that which allows +teachers who have not come into direct contact with the leading facts of +a science to pass their second-hand information on. The scientific virus, +like vaccine lymph, if passed through too long a succession of organisms, +will lose all its effect in protecting the young against the intellectual +epidemics to which they are exposed. + +[The remarks on p. 222 applied to the Natural History Collection of the +British Museum in 1861. The visitor to the Natural History Museum in 1894 +need go no further than the Great Hall to see the realisation of my hopes +by the present Director.]] + + + +VIII + + +BIOGENESIS AND ABIOGENESIS + +(THE PRESIDENTIAL ADDRESS TO THE BRITISH ASSOCIATION FOR THE ADVANCEMENT +OF SCIENCE FOR 1870) + +It has long been the custom for the newly installed President of the +British Association for the Advancement of Science to take advantage of +the elevation of the position in which the suffrages of his colleagues +had, for the time, placed him, and, casting his eyes around the horizon +of the scientific world, to report to them what could be seen from his +watch-tower; in what directions the multitudinous divisions of the noble +army of the improvers of natural knowledge were marching; what important +strongholds of the great enemy of us all, ignorance, had been recently +captured; and, also, with due impartiality, to mark where the advanced +posts of science had been driven in, or a long-continued siege had made +no progress. + +I propose to endeavour to follow this ancient precedent, in a manner +suited to the limitations of my knowledge and of my capacity. I shall not +presume to attempt a panoramic survey of the world of science, nor even +to give a sketch of what is doing in the one great province of biology, +with some portions of which my ordinary occupations render me familiar. +But I shall endeavour to put before you the history of the rise and +progress of a single biological doctrine; and I shall try to give some +notion of the fruits, both intellectual and practical, which we owe, +directly or indirectly, to the working out, by seven generations of +patient and laborious investigators, of the thought which arose, more +than two centuries ago, in the mind of a sagacious and observant Italian +naturalist. + +It is a matter of everyday experience that it is difficult to prevent +many articles of food from becoming covered with mould; that fruit, sound +enough to all appearance, often contains grubs at the core; that meat, +left to itself in the air, is apt to putrefy and swarm with maggots. Even +ordinary water, if allowed to stand in an open vessel, sooner or later +becomes turbid and full of living matter. + +The philosophers of antiquity, interrogated as to the cause of these +phenomena, were provided with a ready and a plausible answer. It did not +enter their minds even to doubt that these low forms of life were +generated in the matters in which they made their appearance. Lucretius, +who had drunk deeper of the scientific spirit than any poet of ancient or +modern times except Goethe, intends to speak as a philosopher, rather +than as a poet, when he writes that "with good reason the earth has +gotten the name of mother, since all things are produced out of the +earth. And many living creatures, even now, spring out of the earth, +taking form by the rains and the heat of the sun."[1] The axiom of +ancient science, "that the corruption of one thing is the birth of +another," had its popular embodiment in the notion that a seed dies +before the young plant springs from it; a belief so widespread and so +fixed, that Saint Paul appeals to it in one of the most splendid +outbursts of his fervid eloquence:-- + +"Thou fool, that which thou sowest is not quickened, except it die."[2] + +[Footnote 1: It is thus that Mr. Munro renders + +"Linquitur, ut merito maternum nomen adepta +Terra sit, e terra quoniam sunt cuncta creata. +Multaque nunc etiam exsistant animalia terris +Imbribus et calido solis concreta vapore." + +_De Rerum Natura_, lib. v. 793-796. + +But would not the meaning of the last line be better rendered "Developed +in rain-water and in the warm vapours raised by the sun"?] + +[Footnote 2: 1 Corinthians xv. 36.] + +The proposition that life may, and does, proceed from that which has no +life, then, was held alike by the philosophers, the poets, and the +people, of the most enlightened nations, eighteen hundred years ago; and +it remained the accepted doctrine of learned and unlearned Europe, +through the Middle Ages, down even to the seventeenth century. + +It is commonly counted among the many merits of our great countryman, +Harvey, that he was the first to declare the opposition of fact to +venerable authority in this, as in other matters; but I can discover no +justification for this widespread notion. After careful search through +the "Exercitationes de Generatione," the most that appears clear to me +is, that Harvey believed all animals and plants to spring from what he +terms a "_primordium vegetale_," a phrase which may nowadays be rendered +"a vegetative germ"; and this, he says, is _"oviforme_," or "egg-like"; +not, he is careful to add, that it necessarily has the shape of an egg, +but because it has the constitution and nature of one. That this +"_primordium oviforme_" must needs, in all cases, proceed from a living +parent is nowhere expressly maintained by Harvey, though such an opinion +may be thought to be implied in one or two passages; while, on the other +hand, he does, more than once, use language which is consistent only with +a full belief in spontaneous or equivocal generation.[3] In fact, the +main concern of Harvey's wonderful little treatise is not with +generation, in the physiological sense, at all, but with development; and +his great object is the establishment of the doctrine of epigenesis. + +[Footnote 3: See the following passage in Exercitatio I.:--"Item _sponte +nascentia_ dicuntur; non quod ex _putredine_ oriunda sint, sed quod casu, +naturae sponte, et aequivocâ (ut aiunt) generatione, a parentibus sui +dissimilibus proveniant." Again, in _De Uteri Membranis:_--"In cunctorum +viventium generatione (sicut diximus) hoc solenne est, ut ortum ducunt a +_primordio_ aliquo, quod tum materiam tum elficiendi potestatem in se +habet: sitque, adeo id, ex quo et a quo quicquid nascitur, ortum suum +ducat. Tale primordium in animalibus (_sive ab aliis generantibus +proveniant, sive sponte, aut ex putredine nascentur_) est humor in +tunicâ, aliquâaut putami ne conclusus." Compare also what Redi has to say +respecting Harvey's opinions, _Esperienze_, p. 11.] + +The first distinct enunciation of the hypothesis that all living matter +has sprung from pre-existing living matter, came from a contemporary, +though a junior, of Harvey, a native of that country, fertile in men +great in all departments of human activity, which was to intellectual +Europe, in the sixteenth and seventeenth centuries, what Germany is in +the nineteenth. It was in Italy, and from Italian teachers, that Harvey +received the most important part of his scientific education. And it was +a student trained in the same schools, Francesco Redi--a man of the +widest knowledge and most versatile abilities, distinguished alike as +scholar, poet, physician, and naturalist--who, just two hundred and two +years ago, published his "Esperienze intorno alla Generazione degl' +Insetti," and gave to the world the idea, the growth of which it is my +purpose to trace. Redi's book went through five editions in twenty years; +and the extreme simplicity of his experiments, and the clearness of his +arguments, gained for his views, and for their consequences, almost +universal acceptance. + +Redi did not trouble himself much with speculative considerations, but +attacked particular cases of what was supposed to be "spontaneous +generation" experimentally. Here are dead animals, or pieces of meat, +says he; I expose them to the air in hot weather, and in a few days they +swarm with maggots. You tell me that these are generated in the dead +flesh; but if I put similar bodies, while quite fresh, into a jar, and +tie some fine gauze over the top of the jar, not a maggot makes its +appearance, while the dead substances, nevertheless, putrefy just in the +same way as before. It is obvious, therefore, that the maggots are not +generated by the corruption of the meat; and that the cause of their +formation must be a something which is kept away by gauze. But gauze will +not keep away aëriform bodies, or fluids. This something must, therefore, +exist in the form of solid particles too big to get through the gauze. +Nor is one long left in doubt what these solid particles are; for the +blowflies, attracted by the odour of the meat, swarm round the vessel, +and, urged by a powerful but in this case misleading instinct, lay eggs +out of which maggots are immediately hatched, upon the gauze. The +conclusion, therefore, is unavoidable; the maggots are not generated by +the meat, but the eggs which give rise to them are brought through the +air by the flies. + +These experiments seem almost childishly simple, and one wonders how it +was that no one ever thought of them before. Simple as they are, however, +they are worthy of the most careful study, for every piece of +experimental work since done, in regard to this subject, has been shaped +upon the model furnished by the Italian philosopher. As the results of +his experiments were the same, however varied the nature of the materials +he used, it is not wonderful that there arose in Redi's mind a +presumption, that, in all such cases of the seeming production of life +from dead matter, the real explanation was the introduction of living +germs from without into that dead matter.[4] And thus the hypothesis that +living matter always arises by the agency of pre-existing living matter, +took definite shape; and had, henceforward, a right to be considered and +a claim to be refuted, in each particular case, before the production of +living matter in any other way could be admitted by careful reasoners. It +will be necessary for me to refer to this hypothesis so frequently, that, +to save circumlocution, I shall call it the hypothesis of _Biogenesis_; +and I shall term the contrary doctrine--that living matter may be +produced by not living matter--the hypothesis of _Abiogenesis_. + +[Footnote 4: "Pure contentandomi sempre in questa ed in ciascuna altro +cosa, da ciascuno più savio, là dove io difettuosamente parlassi, esser +corretto; non tacero, che per molte osservazioni molti volti da me fatte, +mi sento inclinato a credere che la terra, da quelle prime piante, e da +quei primi animali in poi, che ella nei primi giorni del mondo produsse +per comandemento del sovrano ed omnipotente Fattore, non abbia mai più +prodotto da se medesima nè erba nè albero, nè animale alcuno perfetto o +imperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassati +è nato e che ora nascere in lei, o da lei veggiamo, venga tutto dalla +semenza reale e vera delle piante, e degli animali stessi, i quali col +mezzo del proprio seme la loro spezie conservano. E se bene tutto giorno +scorghiamo da' cadaveri degli animali, e da tutte quante le maniere dell' +erbe, e de' fiori, e dei frutti imputriditi, e corrotti nascere vermi +infiniti-- + +'Nonne vides quaecunque mora, fluidoque calore +Corpora tabescunt in parva animalia verti'-- + +Io mi sento, dico, inclinato, a credere che tutti quei vermi si generino +dal seme paterno; e che le carni, e l' erbe, e l' altre cose tutte +putrefatte, o putrefattibili non facciano altra parte, nè abbiano altro +ufizio nella generazione degl' insetti, se non d'apprestare un luogo o un +nido proporzionato, in cui dagli animali nel tempo della figliatura sieno +portati, e partoriti i vermi, o l' uova o l' altre semenze dei vermi, i +quali tosto che nati sono, trovano in esso nido un sufficiente alimento +abilissimo per nutricarsi: e se in quello non son portate dalle madri +queste suddette semenze, niente mai, e replicatamente niente, vi s' +ingegneri e nasca."--REDI, _Esperienze_, pp. 14-16.] + +In the seventeenth century, as I have said, the latter was the dominant +view, sanctioned alike by antiquity and by authority; and it is +interesting to observe that Redi did not escape the customary tax upon a +discoverer of having to defend himself against the charge of impugning +the authority of the Scriptures;[5] for his adversaries declared that the +generation of bees from the carcase of a dead lion is affirmed, in the +Book of Judges, to have been the origin of the famous riddle with which +Samson perplexed the Philistines:-- + +Out of the eater came forth meat, +And out of the strong came forth sweetness. + +[Footnote 5: "Molti, e molti altri ancora vi potrei annoverare, se non +fossi chiamato a rispondere alle rampogne di alcuni, che bruscamente mi +rammentano ciò, che si legge nel capitolo quattordicesimo del sacrosanto +Libro de' giudici ... "--REDI, _loc. cit._ p. 45.] + +Against all odds, however, Redi, strong with the strength of demonstrable +fact, did splendid battle for Biogenesis; but it is remarkable that he +held the doctrine in a sense which, if he lead lived in these times, +would have infallibly caused him to be classed among the defenders of +"spontaneous generation." "Omne vivum ex vivo," "no life without +antecedent life," aphoristically sums up Redi's doctrine; but he went no +further. It is most remarkable evidence of the philosophic caution and +impartiality of his mind, that although he had speculatively anticipated +the manner in which grubs really are deposited in fruits and in the galls +of plants, he deliberately admits that the evidence is insufficient to +bear him out; and he therefore prefers the supposition that they are +generated by a modification of the living substance of the plants +themselves. Indeed, he regards these vegetable growths as organs, by +means of which the plant gives rise to an animal, and looks upon this +production of specific animals as the final cause of the galls and of, at +any rate, some fruits. And he proposes to explain the occurrence of +parasites within the animal body in the same way.[6] + +[Footnote 6: The passage (_Esperienze_, p. 129) is worth quoting in +full:-- + +"Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi, +gli alberi e le foglie, in due maniere inverminassero. Una, perchè +venendo i bachi per dà fuora, e cercando l' alimento, col rodere ci +aprono la strada, ed arrivano alla più interna midolla de' frutti e de' +legni. L'altra maniera si è, che io per me stimerei, che non fosse gran +fatto disdicevole il credere, che quell' anima o quella virtù, la quale +genera i fiori ed i frutti nelle piante viventi, sia quella stessa che +generi ancora i bachi di esse piante. E chi sà , forse, che molti frutti +degli alberi non sieno prodotti, non per un fine primario e principale, +ma bensi per un uffizio secondario e servile, destinato alla generazione +di que' vermi, servendo a loro in vece di matrice, in cui dimorino un +prefisso e determinato tempo; il quale arrivato escan fuora a godere il +sole. + +"Io m' immagino, che questo mio pensiero non vi parrà totalmento un +paradosso; mentro farete riflessione a quelle tanto sorte di galle, di +gallozzole, di coccole, di ricci, di calici, di cornetti ed i lappole, +che son produtte dalle quercel, dalle farnie, da' cerri, da' sugheri, da' +leeci e da altri simili alberi de ghianda; imperciocchè in quello +gallozzole, e particolarmente nelle più grosse, che si chiamano coronati, +ne' ricci capelluti, che ciuffoli da' nostri contadini son detti; nei +ricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzze +della foglia del leccio si vede evidentissimamente, che la prima e +principale intenzione della natura è formare dentro di quelle un animale +volante; vedendosi nel centro della gallozzola un uovo, che col crescere +e col maturarsi di essa gallozzola va crescendo e maturando anch' egli, e +cresce altresi a suo tempo quel verme, che nell' uovo si racchiude; il +qual verme, quando la gallozzola è finita di maturare e che è venuto il +termine destinato al suo nascimento, diventa, di verme che era, una +mosca.... Io vi confesso ingenuamente, che prima d'aver fatte queste mie +esperienze intorno alla generazione degl' insetti mi dava a credere, o +per dir meglio sospettava, che forse la gallozzola nascesse, perchè +arrivando la mosca nel tempo della primavera, e facendo una piccolissima +fessura ne' rami più teneri della quercia, in quella fessura nascondesse +uno de suoi semi, il quale fosse cagione che sbocciasse fuora la +gallozzola; e che mai non si vedessero galle o gallozzole o ricci o +cornetti o calici o coccole, se non in que' rami, ne' quali le mosche +avessero depositate le loro semenze; e mi dava ad intendere, che le +gallozzole fossero una malattia cagionata nelle querce dalle punture +delle mosche, in quella giusa stessa che dalle punture d'altri animaletti +simiglievoli veggiamo crescere de' tumori ne' corpi degli animali."] + +It is of great importance to apprehend Redi's position rightly; for the +lines of thought he laid down for us are those upon which naturalists +have been working ever since. Clearly, he held _Biogenesis_ as against +_Abiogenesis;_ and I shall immediately proceed, in the first place, to +inquire how far subsequent investigation has borne him out in so doing. + +But Redi also thought that there were two modes of Biogenesis. By the one +method, which is that of common and ordinary occurrence, the living +parent gives rise to offspring which passes through the same cycle of +changes as itself--like gives rise to like; and this has been termed +_Homogenesis_. By the other mode, the living parent was supposed to give +rise to offspring which passed through a totally different series of +states from those exhibited by the parent, and did not return into the +cycle of the parent; this is what ought to be called _Heterogenesis_, the +offspring being altogether, and permanently, unlike the parent. The term +Heterogenesis, however, has unfortunately been used in a different sense, +and M. Milne-Edwards has therefore substituted for it _Xenogenesis_, +which means the generation of something foreign. After discussing Redi's +hypothesis of universal Biogenesis, then, I shall go on to ask how far +the growth of science justifies his other hypothesis of Xenogenesis. + +The progress of the hypothesis of Biogenesis was triumphant and unchecked +for nearly a century. The application of the microscope to anatomy in the +hands of Grew, Leeuwenhoek, Swammerdam, Lyonnet, Vallisnieri, Réaurnur, +and other illustrious investigators of nature of that day, displayed such +a complexity of organisation in the lowest and minutest forms, and +everywhere revealed such a prodigality of provision for their +multiplication by germs of one sort or another, that the hypothesis of +Abiogenesis began to appear not only untrue, but absurd; and, in the +middle of the eighteenth century, when Needham and Buffon took up the +question, it was almost universally discredited.[7] + +[Footnote 7: Needham, writing in 1750, says:-- + +"Les naturalistes modernes s'accordent unaninement à établir, comme une +vérité certaine, que toute plante vient do sa sémence spécifique, tout +animal d'un oeuf ou de quelque chose d'analogue préexistant dans la +plante, ou dans l'animal de même espèce qui l'a produit."--_Nouvelles +Observations_, p. 169. + +"Les naturalistes out généralemente cru que les animaux microscopiques +étaient engendrés par des oeufs transportés dans l'air, ou déposés dans +des eaux dormantes par des insectes volans."--_Ibid._ p. 176.] + +But the skill of the microscope makers of the eighteenth century soon +reached its limit. A microscope magnifying 400 diameters was a _chef +d'oeuvre_ of the opticians of that day; and, at the same time, by no +means trustworthy. But a magnifying power of 400 diameters, even when +definition reaches the exquisite perfection of our modern achromatic +lenses, hardly suffices for the mere discernment of the smallest forms of +life. A speck, only 1/25th of an inch in diameter, has, at ten inches +from the eye, the same apparent size as an object 1/10000th of an inch in +diameter, when magnified 400 times; but forms of living matter abound, +the diameter of which is not more than 1/40000th of an inch. A filtered +infusion of hay, allowed to stand for two days, will swarm with living +things among which, any which reaches the diameter of a human red blood- +corpuscle, or about 1/3200th of an inch, is a giant. It is only by +bearing these facts in mind, that we can deal fairly with the remarkable +statements and speculations put forward by Buffon and Needham in the +middle of the eighteenth century. + +When a portion of any animal or vegetable body is infused in water, it +gradually softens and disintegrates; and, as it does so, the water is +found to swarm with minute active creatures, the so-called Infusorial +Animalcules, none of which can be seen, except by the aid of the +microscope; while a large proportion belong to the category of smallest +things of which I have spoken, and which must have looked like mere dots +and lines under the ordinary microscopes of the eighteenth century. + +Led by various theoretical considerations which I cannot now discuss, but +which looked promising enough in the lights of their time, Buffon and +Needham doubted the applicability of Redi's hypothesis to the infusorial +animalcules, and Needham very properly endeavoured to put the question to +an experimental test. He said to himself, If these infusorial animalcules +come from germs, their germs must exist either in the substance infused, +or in the water with which the infusion is made, or in the superjacent +air. Now the vitality of all germs is destroyed by heat. Therefore, if I +boil the infusion, cork it up carefully, cementing the cork over with +mastic, and then heat the whole vessel by heaping hot ashes over it, I +must needs kill whatever germs are present. Consequently, if Redi's +hypothesis hold good, when the infusion is taken away and allowed to +cool, no animalcules ought to be developed in it; whereas, if the +animalcules are not dependent on pre-existing germs, but are generated +from the infused substance, they ought, by and by, to make their +appearance. Needham found that, under the circumstances in which he made +his experiments, animalcules always did arise in the infusions, when a +sufficient time had elapsed to allow for their development. + +In much of his work Needham was associated with Buffon, and the results +of their experiments fitted in admirably with the great French +naturalist's hypothesis of "organic molecules," according to which, life +is the indefeasible property of certain indestructible molecules of +matter, which exist in all living things, and have inherent activities by +which they are distinguished from not living matter. Each individual +living organism is formed by their temporary combination. They stand to +it in the relation of the particles of water to a cascade, or a +whirlpool; or to a mould, into which the water is poured. The form of the +organism is thus determined by the reaction between external conditions +and the inherent activities of the organic molecules of which it is +composed; and, as the stoppage of a whirlpool destroys nothing but a +form, and leaves the molecules of the water, with all their inherent +activities intact, so what we call the death and putrefaction of an +animal, or of a plant, is merely the breaking up of the form, or manner +of association, of its constituent organic molecules, which are then set +free as infusorial animalcules. + +It will be perceived that this doctrine is by no means identical with +_Abiogenesis_, with which it is often confounded. On this hypothesis, a +piece of beef, or a handful of hay, is dead only in a limited sense. The +beef is dead ox, and the hay is dead grass; but the "organic molecules" +of the beef or the hay are not dead, but are ready to manifest their +vitality as soon as the bovine or herbaceous shrouds in which they are +imprisoned are rent by the macerating action of water. The hypothesis +therefore must be classified under Xenogenesis, rather than under +Abiogenesis. Such as it was, I think it will appear, to those who will be +just enough to remember that it was propounded before the birth of modern +chemistry, and of the modern optical arts, to be a most ingenious and +suggestive speculation. + +But the great tragedy of Science--the slaying of a beautiful hypothesis +by an ugly fact--which is so constantly being enacted under the eyes of +philosophers, was played, almost immediately, for the benefit of Buffon +and Needham. + +Once more, an Italian, the Abbé Spallanzani, a worthy successor and +representative of Redi in his acuteness, his ingenuity, and his learning, +subjected the experiments and the conclusions of Needham to a searching +criticism. It might be true that Needham's experiments yielded results +such as he had described, but did they bear out his arguments? Was it not +possible, in the first place, he had not completely excluded the air by +his corks and mastic? And was it not possible, in the second place, that +he had not sufficiently heated his infusions and the superjacent air? +Spallanzani joined issue with the English naturalist on both these pleas, +and he showed that if, in the first place, the glass vessels in which the +infusions were contained were hermetically sealed by fusing their necks, +and if, in the second place, they were exposed to the temperature of +boiling water for three-quarters of an hour,[8] no animalcules ever made +their appearance within them. It must be admitted that the experiments +and arguments of Spallanzani furnish a complete and a crushing reply to +those of Needham. But we all too often forget that it is one thing to +refute a proposition, and another to prove the truth of a doctrine which, +implicitly or explicitly, contradicts that proposition; and the advance +of science soon showed that though Needham might be quite wrong, it did +not follow that Spallanzani was quite right. + +[Footnote 8: See Spallanzani, _Opere_, vi. pp. 42 and 51.] + +Modern Chemistry, the birth of the latter half of the eighteenth century, +grew apace, and soon found herself face to face with the great problems +which biology had vainly tried to attack without her help. The discovery +of oxygen led to the laying of the foundations of a scientific theory of +respiration, and to an examination of the marvellous interactions of +organic substances with oxygen. The presence of free oxygen appeared to +be one of the conditions of the existence of life, and of those singular +changes in organic matters which are known as fermentation and +putrefaction. The question of the generation of the infusory animalcules +thus passed into a new phase. For what might not have happened to the +organic matter of the infusions, or to the oxygen of the air, in +Spallanzani's experiments? What security was there that the development +of life which ought to have taken place had not been checked or prevented +by these changes? + +The battle had to be fought again. It was needful to repeat the +experiments under conditions which would make sure that neither the +oxygen of the air, nor the composition of the organic matter, was altered +in such a manner as to interfere with the existence of life. + +Schulze and Schwann took up the question from this point of view in 1836 +and 1837. The passage of air through red-hot glass tubes, or through +strong sulphuric acid, does not alter the proportion of its oxygen, while +it must needs arrest, or destroy, any organic matter which may be +contained in the air. These experimenters, therefore, contrived +arrangements by which the only air which should come into contact with a +boiled infusion should be such as had either passed through red-hot tubes +or through strong sulphuric acid. The result which they obtained was that +an infusion so treated developed no living things, while, if the same +infusion was afterwards exposed to the air, such things appeared rapidly +and abundantly. The accuracy of these experiments has been alternately +denied and affirmed. Supposing then, to be accepted, however, all that +they really proved was that the treatment to which the air was subjected +destroyed _something_ that was essential to the development of life in +the infusion. This "something" might be gaseous, fluid, or solid; that it +consisted of germs remained only an hypothesis of greater or less +probability. + +Contemporaneously with these investigations a remarkable discovery was +made by Cagniard de la Tour. He found that common yeast is composed of a +vast accumulation of minute plants. The fermentation of must, or of wort, +in the fabrication of wine and of beer, is always accompanied by the +rapid growth and multiplication of these _Toruloe_. Thus, fermentation, +in so far as it was accompanied by the development of microscopical +organisms in enormous numbers, became assimilated to the decomposition of +an infusion of ordinary animal or vegetable matter; and it was an obvious +suggestion that the organisms were, in some way or other, the causes both +of fermentation and of putrefaction. The chemists, with Berzelius and +Liebig at their head, at first laughed this idea to scorn; but in 1843, a +man then very young, who has since performed the unexampled feat of +attaining to high eminence alike in Mathematics, Physics, and Physiology-- +I speak of the illustrious Helmholtz--reduced the matter to the test of +experiment by a method alike elegant and conclusive. Helmholtz separated +a putrefying or a fermenting liquid from one which was simply putrescible +or fermentable by a membrane which allowed the fluids to pass through and +become intermixed, but stopped the passage of solids. The result was, +that while the putrescible or the fermentable liquids became impregnated +with the results of the putrescence or fermentation which was going on on +the other side of the membrane, they neither putrefied (in the ordinary +way) nor fermented; nor were any of the organisms which abounded in the +fermenting or putrefying liquid generated in them. Therefore the cause of +the development of these organisms must lie in something which cannot +pass through membranes; and as Helmholtz's investigations were long +antecedent to Graham's researches upon colloids, his natural conclusion +was that the agent thus intercepted must be a solid material. In point of +fact, Helmholtz's experiments narrowed the issue to this: that which +excites fermentation and putrefaction, and at the same time gives rise to +living forms in a fermentable or putrescible fluid, is not a gas and is +not a diffusible fluid; therefore it is either a colloid, or it is matter +divided into very minute solid particles. + +The researches of Schroeder and Dusch in 1854, and of Schroeder alone, in +1859, cleared up this point by experiments which are simply refinements +upon those of Redi. A lump of cotton-wool is, physically speaking, a pile +of many thicknesses of a very fine gauze, the fineness of the meshes of +which depends upon the closeness of the compression of the wool. Now, +Schroeder and Dusch found, that, in the case of all the putrefiable +materials which they used (except milk and yolk of egg), an infusion +boiled, and then allowed to come into contact with no air but such as had +been filtered through cotton-wool, neither putrefied, nor fermented, nor +developed living forms. It is hard to imagine what the fine sieve formed +by the cotton-wool could have stopped except minute solid particles. +Still the evidence was incomplete until it had been positively shown, +first, that ordinary air does contain such particles; and, secondly, that +filtration through cotton-wool arrests these particles and allows only +physically pure air to pass. This demonstration has been furnished within +the last year by the remarkable experiments of Professor Tyndall. It has +been a common objection of Abiogenists that, if the doctrine of Biogeny +is true, the air must be thick with germs; and they regard this as the +height of absurdity. But nature occasionally is exceedingly unreasonable, +and Professor Tyndall has proved that this particular absurdity may +nevertheless be a reality. He has demonstrated that ordinary air is no +better than a sort of stirabout of excessively minute solid particles; +that these particles are almost wholly destructible by heat; and that +they are strained off, and the air rendered optically pure, by its being +passed through cotton-wool. + +It remains yet in the order of logic, though not of history, to show that +among these solid destructible particles, there really do exist germs +capable of giving rise to the development of living forms in suitable +menstrua. This piece of work was done by M. Pasteur in those beautiful +researches which will ever render his name famous; and which, in spite of +all attacks upon them, appear to me now, as they did seven years ago,[9] +to be models of accurate experimentation and logical reasoning. He +strained air through cotton-wool, and found, as Schroeder and Dusch had +done, that it contained nothing competent to give rise to the development +of life in fluids highly fitted for that purpose. But the important +further links in the chain of evidence added by Pasteur are three. In the +first place he subjected to microscopic examination the cotton-wool which +had served as strainer, and found that sundry bodies clearly recognisable +as germs, were among the solid particles strained off. Secondly, he +proved that these germs were competent to give rise to living forms by +simply sowing them in a solution fitted for their development. And, +thirdly, he showed that the incapacity of air strained through cotton- +wool to give rise to life, was not due to any occult change effected in +the constituents of the air by the wool, by proving that the cotton-wool +might be dispensed with altogether, and perfectly free access left +between the exterior air and that in the experimental flask. If the neck +of the flask is drawn out into a tube and bent downwards; and if, after +the contained fluid has been carefully boiled, the tube is heated +sufficiently to destroy any germs which may be present in the air which +enters as the fluid cools, the apparatus may be left to itself for any +time and no life will appear in the fluid. The reason is plain. Although +there is free communication between the atmosphere laden with germs and +the germless air in the flask, contact between the two takes place only +in the tube; and as the germs cannot fall upwards, and there are no +currents, they never reach the interior of the flask. But if the tube be +broken short off where it proceeds from the flask, and free access be +thus given to germs falling vertically out of the air, the fluid, which +has remained clear and desert for months, becomes, in a few days, turbid +and full of life. + +[Footnote 9: _Lectures to Working Men on the Causes of the Phenomena of +Organic Nature_, 1863. (See Vol. II. of these Essays.)] + +These experiments have been repeated over and over again by independent +observers with entire success; and there is one very simple mode of +seeing the facts for one's self, which I may as well describe. + +Prepare a solution (much used by M. Pasteur, and often called "Pasteur's +solution") composed of water with tartrate of ammonia, sugar, and yeast- +ash dissolved therein.[10] Divide it into three portions in as many +flasks; boil all three for a quarter of an hour; and, while the steam is +passing out, stop the neck of one with a large plug of cotton-wool, so +that this also may be thoroughly steamed. Now set the flasks aside to +cool, and, when their contents are cold, add to one of the open ones a +drop of filtered infusion of hay which has stood for twenty-four hours, +and is consequently hill of the active and excessively minute organisms +known as _Bacteria_. In a couple of days of ordinary warm weather the +contents of this flask will be milky from the enormous multiplication of +_Bacteria_. The other flask, open and exposed to the air, will, sooner or +later, become milky with _Bacteria_, and patches of mould may appear in +it; while the liquid in the flask, the neck of which is plugged with +cotton-wool, will remain clear for an indefinite time. I have sought in +vain for any explanation of these facts, except the obvious one, that the +air contains germs competent to give rise to _Bacteria_, such as those +with which the first solution has been knowingly and purposely +inoculated, and to the mould-_Fungi_. And I have not yet been able to +meet with any advocate of Abiogenesis who seriously maintains that the +atoms of sugar, tartrate of ammonia, yeast-ash, and water, under no +influence but that of free access of air and the ordinary temperature, +re-arrange themselves and give rise to the protoplasm of _Bacterium_. But +the alternative is to admit that these _Bacteria_ arise from germs in the +air; and if they are thus propagated, the burden of proof that other like +forms are generated in a different manner, must rest with the assertor of +that proposition. + +[Footnote 10: Infusion of hay treated in the same way yields similar +results; but as it contains organic matter, the argument which follows +cannot be based upon it.] + +To sum up the effect of this long chain of evidence:-- + +It is demonstrable that a fluid eminently fit for the development of the +lowest forms of life, but which contains neither germs, nor any protein +compound, gives rise to living things in great abundance if it is exposed +to ordinary air; while no such development takes place, if the air with +which it is in contact is mechanically freed from the solid particles +which ordinarily float in it, and which may be made visible by +appropriate means. + +It is demonstrable that the great majority of these particles are +destructible by heat, and that some of them are germs, or living +particles, capable of giving rise to the same forms of life as those +which appear when the fluid is exposed to unpurified air. + +It is demonstrable that inoculation of the experimental fluid with a drop +of liquid known to contain living particles gives rise to the same +phenomena as exposure to unpurified air. + +And it is further certain that these living particles are so minute that +the assumption of their suspension in ordinary air presents not the +slightest difficulty. On the contrary, considering their lightness and +the wide diffusion of the organisms which produce them, it is impossible +to conceive that they should not be suspended in the atmosphere in +myriads. + +Thus the evidence, direct and indirect, in favour of _Biogenesis_ for all +known forms of life must, I think, be admitted to be of great weight. + +On the other side, the sole assertions worthy of attention are that +hermetically sealed fluids, which have been exposed to great and long- +continued heat, have sometimes exhibited living forms of low organisation +when they have been opened. + +The first reply that suggests itself is the probability that there must +be some error about these experiments, because they are performed on an +enormous scale every day with quite contrary results. Meat, fruits, +vegetables, the very materials of the most fermentable and putrescible +infusions, are preserved to the extent, I suppose I may say, of thousands +of tons every year, by a method which is a mere application of +Spallanzani's experiment. The matters to be preserved are well boiled in +a tin case provided with a small hole, and this hole is soldered up when +all the air in the case has been replaced by steam. By this method they +may be kept for years without putrefying, fermenting, or getting mouldy. +Now this is not because oxygen is excluded, inasmuch as it is now proved +that free oxygen is not necessary for either fermentation or +putrefaction. It is not because the tins are exhausted of air, for +_Vibriones_ and _Bacteria_ live, as Pasteur has shown, without air or +free oxygen. It is not because the boiled meats or vegetables are not +putrescible or fermentable, as those who have had the misfortune to be in +a ship supplied with unskilfully closed tins well know. What is it, +therefore, but the exclusion of germs? I think that Abiogenists are bound +to answer this question before they ask us to consider new experiments of +precisely the same order. + +And in the next place, if the results of the experiments I refer to are +really trustworthy, it by no means follows that Abiogenesis has taken +place. The resistance of living matter to heat is known to vary within +considerable limits, and to depend, to some extent, upon the chemical and +physical qualities of the surrounding medium. But if, in the present +state of science, the alternative is offered us,--either germs can stand +a greater heat than has been supposed, or the molecules of dead matter, +for no valid or intelligible reason that is assigned, are able to re- +arrange themselves into living bodies, exactly such as can be +demonstrated to be frequently produced in another way,--I cannot +understand how choice can be, even for a moment, doubtful. + +But though I cannot express this conviction of mine too strongly, I must +carefully guard myself against the supposition that I intend to suggest +that no such thing as Abiogenesis ever has taken place in the past, or +ever will take place in the future. With organic chemistry, molecular +physics, and physiology yet in their infancy, and every day making +prodigious strides, I think it would be the height of presumption for any +man to say that the conditions under which matter assumes the properties +we call "vital" may not, some day, be artificially brought together. All +I feel justified in affirming is, that I see no reason for believing that +the feat has been performed yet. + +And looking back through the prodigious vista of the past, I find no +record of the commencement of life, and therefore I am devoid of any +means of forming a definite conclusion as to the conditions of its +appearance. Belief, in the scientific sense of the word, is a serious +matter, and needs strong foundations. To say, therefore, in the admitted +absence of evidence, that I have any belief as to the mode in which the +existing forms of life have originated, would be using words in a wrong +sense. But expectation is permissible where belief is not; and if it were +given me to look beyond the abyss of geologically recorded time to the +still more remote period when the earth was passing through physical and +chemical conditions, which it can no more see again than a man can recall +his infancy, I should expect to be a witness of the evolution of living +protoplasm from not living matter. I should expect to see it appear under +forms of great simplicity, endowed, like existing fungi, with the power +of determining the formation of new protoplasm from such matters as +ammonium carbonates, oxalates and tartrates, alkaline and earthy +phosphates, and water, without the aid of light. That is the expectation +to which analogical reasoning leads me; but I beg you once more to +recollect that I have no right to call my opinion anything but an act of +philosophical faith. + +So much for the history of the progress of Redi's great doctrine of +Biogenesis, which appears to me, with the limitations I have expressed, +to be victorious along the whole line at the present day. + +As regards the second problem offered to us by Redi, whether Xenogenesis +obtains, side by side with Homogenesis,--whether, that is, there exist +not only the ordinary living things, giving rise to offspring which run +through the same cycle as themselves, but also others, producing +offspring which are of a totally different character from themselves,-- +the researches of two centuries have led to a different result. That the +grubs found in galls are no product of the plants on which the galls +grow, but are the result of the introduction of the eggs of insects into +the substance of these plants, was made out by Vallisnieri, Réaumur, and +others, before the end of the first half of the eighteenth century. The +tapeworms, bladderworms, and flukes continued to be a stronghold of the +advocates of Xenogenesis for a much longer period. Indeed, it is only +within the last thirty years that the splendid patience of Von Siebold, +Van Beneden, Leuckart, Küchenmeister, and other helminthologists, has +succeeded in tracing every such parasite, often through the strangest +wanderings and metamorphoses, to an egg derived from a parent, actually +or potentially like itself; and the tendency of inquiries elsewhere has +all been in the same direction. A plant may throw off bulbs, but these, +sooner or later, give rise to seeds or spores, which develop into the +original form. A polype may give rise to Medusae, or a pluteus to an +Echinoderm, but the Medusa and the Echinoderm give rise to eggs which +produce polypes or glutei, and they are therefore only stages in the +cycle of life of the species. + +But if we turn to pathology, it offers us some remarkable approximations +to true Xenogenesis. + +As I have already mentioned, it has been known since the time of +Vallisnieri and of Réaumur, that galls in plants, and tumours in cattle, +are caused by insects, which lay their eggs in those parts of the animal +or vegetable frame of which these morbid structures are outgrowths. +Again, it is a matter of familiar experience to everybody that mere +pressure on the skin will give rise to a corn. Now the gall, the tumour, +and the corn are parts of the living body, which have become, to a +certain degree, independent and distinct organisms. Under the influence +of certain external conditions, elements of the body, which should have +developed in due subordination to its general plan, set up for themselves +and apply the nourishment which they receive to their own purposes. + +From such innocent productions as corns and warts, there are all +gradations to the serious tumours which, by their mere size and the +mechanical obstruction they cause, destroy the organism out of which they +are developed; while, finally, in those terrible structures known as +cancers, the abnormal growth has acquired powers of reproduction and +multiplication, and is only morphologically distinguishable from the +parasitic worm, the life of which is neither more nor less closely bound +up with that of the infested organism. + +If there were a kind of diseased structure, the histological elements of +which were capable of maintaining a separate and independent existence +out of the body, it seems to me that the shadowy boundary between morbid +growth and Xenogenesis would be effaced. And I am inclined to think that +the progress of discovery has almost brought us to this point already. I +have been favoured by Mr. Simon with an early copy of the last published +of the valuable "Reports on the Public Health," which, in his capacity of +their medical officer, he annually presents to the Lords of the Privy +Council. The appendix to this report contains an introductory essay "On +the Intimate Pathology of Contagion," by Dr. Burdon-Sanderson, which is +one of the clearest, most comprehensive, and well-reasoned discussions of +a great question which has come under my notice for a long time. I refer +you to it for details and for the authorities for the statements I am +about to make. + +You are familiar with what happens in vaccination. A minute cut is made +in the skin, and an infinitesimal quantity of vaccine matter is inserted +into the wound. Within a certain time a vesicle appears in the place of +the wound, and the fluid which distends this vesicle is vaccine matter, +in quantity a hundred or a thousandfold that which was originally +inserted. Now what has taken place in the course of this operation? Has +the vaccine matter, by its irritative property, produced a mere blister, +the fluid of which has the same irritative property? Or does the vaccine +matter contain living particles, which have grown and multiplied where +they have been planted? The observations of M. Chauveau, extended and +confirmed by Dr. Sanderson himself, appear to leave no doubt upon this +head. Experiments, similar in principle to those of Helmholtz on +fermentation and putrefaction, have proved that the active element in the +vaccine lymph is non-diffusible, and consists of minute particles not +exceeding 1/20000th of an inch in diameter, which are made visible in the +lymph by the microscope. Similar experiments have proved that two of the +most destructive of epizootic diseases, sheep-pox and glanders, are also +dependent for their existence and their propagation upon extremely small +living solid particles, to which the title of _microzymes_ is applied. An +animal suffering under either of these terrible diseases is a source of +infection and contagion to others, for precisely the same reason as a tub +of fermenting beer is capable of propagating its fermentation by +"infection," or "contagion," to fresh wort. In both cases it is the solid +living particles which are efficient; the liquid in which they float, and +at the expense of which they live, being altogether passive. + +Now arises the question, are these microzymes the results of +_Homogenesis_, or of _Xenogenesis?_ are they capable, like the +_Toruloe_ of yeast, of arising only by the development of pre-existing +germs? or may they be, like the constituents of a nut-gall, the results +of a modification and individualisation of the tissues of the body in +which they are found, resulting from the operation of certain conditions? +Are they parasites in the zoological sense, or are they merely what +Virchow has called "heterologous growths"? It is obvious that this +question has the most profound importance, whether we look at it from a +practical or from a theoretical point of view. A parasite may be stamped +out by destroying its germs, but a pathological product can only be +annihilated by removing the conditions which give rise to it. + +It appears to me that this great problem will have to be solved for each +zymotic disease separately, for analogy cuts two ways. I have dwelt upon +the analogy of pathological modification, which is in favour of the +xenogenetic origin of microzymes; but I must now speak of the equally +strong analogies in favour of the origin of such pestiferous particles by +the ordinary process of the generation of like from like. + +It is, at present, a well-established fact that certain diseases, both of +plants and of animals, which have all the characters of contagious and +infectious epidemics, are caused by minute organisms. The smut of wheat +is a well-known instance of such a disease, and it cannot be doubted that +the grape-disease and the potato-disease fall under the same category. +Among animals, insects are wonderfully liable to the ravages of +contagious and infectious diseases caused by microscopic _Fungi_. + +In autumn, it is not uncommon to see flies motionless upon a window-pane, +with a sort of magic circle, in white, drawn round them. On microscopic +examination, the magic circle is found to consist of innumerable spores, +which have been thrown off in all directions by a minute fungus called +_Empusa muscoe_, the spore-forming filaments of which stand out like a +pile of velvet from the body of the fly. These spore-forming filaments +are connected with others which fill the interior of the fly's body like +so much fine wool, having eaten away and destroyed the creature's +viscera. This is the full-grown condition of the _Empusa_. If traced back +to its earliest stages, in flies which are still active, and to all +appearance healthy, it is found to exist in the form of minute corpuscles +which float in the blood of the fly. These multiply and lengthen into +filaments, at the expense of the fly's substance; and when they have at +last killed the patient, they grow out of its body and give off spores. +Healthy flies shut up with diseased ones catch this mortal disease, and +perish like the others. A most competent observer, M. Cohn, who studied +the development of the _Empusa_ very carefully, was utterly unable to +discover in what manner the smallest germs of the _Empusa_ got into the +fly. The spores could not be made to give rise to such germs by +cultivation; nor were such germs discoverable in the air, or in the food +of the fly. It looked exceedingly like a case of Abiogenesis, or, at any +rate, of Xenogenesis; and it is only quite recently that the real course +of events has been made out. It has been ascertained, that when one of +the spores falls upon the body of a fly, it begins to germinate, and +sends out a process which bores its way through the fly's skin; this, +having reached the interior cavities of its body, gives off the minute +floating corpuscles which are the earliest stage of the _Empusa_. The +disease is "contagious," because a healthy fly coming in contact with a +diseased one, from which the spore-bearing filaments protrude, is pretty +sure to carry off a spore or two. It is "infectious" because the spores +become scattered about all sorts of matter in the neighbourhood of the +slain flies. + +The silkworm has long been known to be subject to a very fatal and +infectious disease called the _Muscardine_. Audouin transmitted it by +inoculation. This disease is entirely due to the development of a fungus, +_Botrytis Bassiana_, in the body of the caterpillar; and its +contagiousness and infectiousness are accounted for in the same way as +those of the fly-disease. But, of late years, a still more serious +epizootic has appeared among the silkworms; and I may mention a few facts +which will give you some conception of the gravity of the injury which it +has inflicted on France alone. + +The production of silk has been for centuries an important branch of +industry in Southern France, and in the year 1853 it had attained such a +magnitude that the annual produce of the French sericulture was estimated +to amount to a tenth of that of the whole world, and represented a money- +value of 117,000,000 francs, or nearly five millions sterling. What may +be the sum which would represent the money-value of all the industries +connected with the working up of the raw silk thus produced, is more than +I can pretend to estimate. Suffice it to say, that the city of Lyons is +built upon French silk as much as Manchester was upon American cotton +before the civil war. + +Silkworms are liable to many diseases; and, even before 1853, a peculiar +epizootic, frequently accompanied by the appearance of dark spots upon +the skin (whence the name of "Pébrine" which it has received), had been +noted for its mortality. But in the years following 1853 this malady +broke out with such extreme violence, that, in 1858, the silk-crop was +reduced to a third of the amount which it had reached in 1853; and, up +till within the last year or two, it has never attained half the yield of +1853. This means not only that the great number of people engaged in silk +growing are some thirty millions sterling poorer than they might have +been; it means not only that high prices have had to be paid for imported +silkworm eggs, and that, after investing his money in them, in paying for +mulberry-leaves and for attendance, the cultivator has constantly seen +his silkworms perish and himself plunged in ruin; but it means that the +looms of Lyons have lacked employment, and that, for years, enforced +idleness and misery have been the portion of a vast population which, in +former days, was industrious and well-to-do. + +In 1858 the gravity of the situation caused the French Academy of +Sciences to appoint Commissioners, of whom a distinguished naturalist, M. +de Quatrefages, was one, to inquire into the nature of this disease, and, +if possible, to devise some means of staying the plague. In reading the +Report[11] made by M. de Quatrefages in 1859, it is exceedingly +interesting to observe that his elaborate study of the Pébrine forced the +conviction upon his mind that, in its mode of occurrence and propagation, +the disease of the silkworm is, in every respect, comparable to the +cholera among mankind. But it differs from the cholera, and so far is a +more formidable malady, in being hereditary, and in being, under some +circumstances, contagious as well as infectious. + +[Footnote 11: _Études sur les Maladies actuelles des Vers à Soie_, p. +53.] + +The Italian naturalist, Filippi, discovered in the blood of the silkworms +affected by this strange disorder a multitude of cylindrical corpuscles, +each about 1/6000th of an inch long. These have been carefully studied by +Lebert, and named by him _Panhistophyton_; for the reason that in +subjects in which the disease is strongly developed, the corpuscles swarm +in every tissue and organ of the body, and even pass into the undeveloped +eggs of the female moth. But are these corpuscles causes, or mere +concomitants, of the disease? Some naturalists took one view and some +another; and it was not until the French Government, alarmed by the +continued ravages of the malady, and the inefficiency of the remedies +which had been suggested, despatched M. Pasteur to study it, that the +question received its final settlement; at a great sacrifice, not only of +the time and peace of mind of that eminent philosopher, but, I regret to +have to add, of his health. + +But the sacrifice has not been in vain. It is now certain that this +devastating, cholera-like, Pébrine, is the effect of the growth and +multiplication of the _Panhistophyton_ in the silkworm. It is contagious +and infectious, because the corpuscles of the _Panhistophyton_ pass away +from the bodies of the diseased caterpillars, directly or indirectly, to +the alimentary canal of healthy silkworms in their neighbourhood; it is +hereditary because the corpuscles enter into the eggs while they are +being formed, and consequently are carried within them when they are +laid; and for this reason, also, it presents the very singular +peculiarity of being inherited only on the mother's side. There is not a +single one of all the apparently capricious and unaccountable phenomena +presented by the Pébrine, but has received its explanation from the fact +that the disease is the result of the presence of the microscopic +organism, _Panhistophyton_. + +Such being the facts with respect to the Pébrine, what are the +indications as to the method of preventing it? It is obvious that this +depends upon the way in which the _Panhistophyton_ is generated. If it +may be generated by Abiogenesis, or by Xenogenesis, within the silkworm +or its moth, the extirpation of the disease must depend upon the +prevention of the occurrence of the conditions under which this +generation takes place. But if, on the other hand, the _Panhistophyton_ +is an independent organism, which is no more generated by the silkworm +than the mistletoe is generated by the apple-tree or the oak on which it +grows, though it may need the silkworm for its development in the same +way as the mistletoe needs the tree, then the indications are totally +different. The sole thing to be done is to get rid of and keep away the +germs of the _Panhistophyton_. As might be imagined, from the course of +his previous investigations, M. Pasteur was led to believe that the +latter was the right theory; and, guided by that theory, he has devised a +method of extirpating the disease, which has proved to be completely +successful wherever it has been properly carried out. + +There can be no reason, then, for doubting that, among insects, +contagious and infectious diseases, of great malignity, are caused by +minute organisms which are produced from pre-existing germs, or by +homogenesis; and there is no reason, that I know of, for believing that +what happens in insects may not take place in the highest animals. +Indeed, there is already strong evidence that some diseases of an +extremely malignant and fatal character to which man is subject, are as +much the work of minute organisms as is the Pébrine. I refer for this +evidence to the very striking facts adduced by Professor Lister in his +various well-known publications on the antiseptic method of treatment. It +appears to me impossible to rise from the perusal of those publications +without a strong conviction that the lamentable mortality which so +frequently dogs the footsteps of the most skilful operator, and those +deadly consequences of wounds and injuries which seem to haunt the very +walls of great hospitals, and are, even now, destroying more men than die +of bullet or bayonet, are due to the importation of minute organisms into +wounds, and their increase and multiplication; and that the surgeon who +saves most lives will be he who best works out the practical consequences +of the hypothesis of Redi. + +I commenced this Address by asking you to follow me in an attempt to +trace the path which has been followed by a scientific idea, in its long +and slow progress from the position of a probable hypothesis to that of +an established law of nature. Our survey has not taken us into very +attractive regions; it has lain, chiefly, in a land flowing with the +abominable, and peopled with mere grubs and mouldiness. And it may be +imagined with what smiles and shrugs, practical and serious +contemporaries of Redi and of Spallanzani may have commented on the waste +of their high abilities in toiling at the solution of problems which, +though curious enough in themselves, could be of no conceivable utility +to mankind. + +Nevertheless, you will have observed that before we had travelled very +far upon our road, there appeared, on the right hand and on the left, +fields laden with a harvest of golden grain, immediately convertible into +those things which the most solidly practical men will admit to have +value--viz., money and life. + +The direct loss to France caused by the Pébrine in seventeen years cannot +be estimated at less than fifty millions sterling; and if we add to this +what Redi's idea, in Pasteur's hands, has done for the wine-grower and +for the vinegar-maker, and try to capitalise its value, we shall find +that it will go a long way towards repairing the money losses caused by +the frightful and calamitous war of this autumn. And as to the equivalent +of Redi's thought in life, how can we over-estimate the value of that +knowledge of the nature of epidemic and epizootic diseases, and +consequently of the means of checking, or eradicating them, the dawn of +which has assuredly commenced? + +Looking back no further than ten years, it is possible to select three +(1863, 1864, and 1869) in which the total number of deaths from scarlet- +fever alone amounted to ninety thousand. That is the return of killed, +the maimed and disabled being left out of sight. Why, it is to be hoped +that the list of killed in the present bloodiest of all wars will not +amount to more than this! But the facts which I have placed before you +must leave the least sanguine without a doubt that the nature and the +causes of this scourge will, one day, be as well understood as those of +the Pébrine are now; and that the long-suffered massacre of our innocents +will come to an end. + +And thus mankind will have one more admonition that "the people perish +for lack of knowledge"; and that the alleviation of the miseries, and the +promotion of the welfare, of men must be sought, by those who will not +lose their pains, in that diligent, patient, loving study of all the +multitudinous aspects of Nature, the results of which constitute exact +knowledge, or Science. It is the justification and the glory of this +great meeting that it is gathered together for no other object than the +advancement of the moiety of science which deals with those phenomena of +nature which we call physical. May its endeavours be crowned with a full +measure of success! + + + +IX + + +GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE + +[1862] + +Merchants occasionally go through a wholesome, though troublesome and not +always satisfactory, process which they term "taking stock." After all +the excitement of speculation, the pleasure of gain, and the pain of +loss, the trader makes up his mind to face facts and to learn the exact +quantity and quality of his solid and reliable possessions. + +The man of science does well sometimes to imitate this procedure; and, +forgetting for the time the importance of his own small winnings, to re- +examine the common stock in trade, so that he may make sure how far the +stock of bullion in the cellar--on the faith of whose existence so much +paper has been circulating--is really the solid gold of truth. + +The Anniversary Meeting of the Geological Society seems to be an occasion +well suited for an undertaking of this kind--for an inquiry, in fact, +into the nature and value of the present results of palaeontological +investigation; and the more so, as all those who have paid close +attention to the late multitudinous discussions in which palaeontology is +implicated, must have felt the urgent necessity of some such scrutiny. + +First in order, as the most definite and unquestionable of all the +results of palaeontology, must be mentioned the immense extension and +impulse given to botany, zoology, and comparative anatomy, by the +investigation of fossil remains. Indeed, the mass of biological facts has +been so greatly increased, and the range of biological speculation has +been so vastly widened, by the researches of the geologist and +palaeontologist, that it is to be feared there are naturalists in +existence who look upon geology as Brindley regarded rivers. "Rivers," +said the great engineer, "were made to feed canals;" and geology, some +seem to think, was solely created to advance comparative anatomy. + +Were such a thought justifiable, it could hardly expect to be received +with favour by this assembly. But it is not justifiable. Your favourite +science has her own great aims independent of all others; and if, +notwithstanding her steady devotion to her own progress, she can scatter +such rich alms among her sisters, it should be remembered that her +charity is of the sort that does not impoverish, but "blesseth him that +gives and him that takes." + +Regard the matter as we will, however, the facts remain. Nearly 40,000 +species of animals and plants have been added to the Systema Naturae by +palaeontological research. This is a living population equivalent to that +of a new continent in mere number; equivalent to that of a new +hemisphere, if we take into account the small population of insects as +yet found fossil, and the large proportion and peculiar organisation of +many of the Vertebrata. + +But, beyond this, it is perhaps not too much to say that, except for the +necessity of interpreting palaeontological facts, the laws of distribution +would have received less careful study; while few comparative anatomists +(and those not of the first order) would have been induced by mere love +of detail, as such, to study the minutiae of osteology, were it not that +in such minutiae lie the only keys to the most interesting riddles offered +by the extinct animal world. + +These assuredly are great and solid gains. Surely it is matter for no +small congratulation that in half a century (for palaeontology, though it +dawned earlier, came into full day only with Cuvier) a subordinate branch +of biology should have doubled the value and the interest of the whole +group of sciences to which it belongs. + +But this is not all. Allied with geology, palaeontology has established +two laws of inestimable importance: the first, that one and the same area +of the earth's surface has been successively occupied by very different +kinds of living beings; the second, that the order of succession +established in one locality holds good, approximately, in all. + +The first of these laws is universal and irreversible; the second is an +induction from a vast number of observations, though it may possibly, and +even probably, have to admit of exceptions. As a consequence of the +second law, it follows that a peculiar relation frequently subsists +between series of strata containing organic remains, in different +localities. The series resemble one another not only in virtue of a +general resemblance of the organic remains in the two, but also in virtue +of a resemblance in the order and character of the serial succession in +each. There is a resemblance of arrangement; so that the separate terms +of each series, as well as the whole series, exhibit a correspondence. + +Succession implies time; the lower members of an undisturbed series of +sedimentary rocks are certainly older than the upper; and when the notion +of age was once introduced as the equivalent of succession, it was no +wonder that correspondence in succession came to be looked upon as a +correspondence in age, or "contemporaneity." And, indeed, so long as +relative age only is spoken of, correspondence in succession _is_ +correspondence in age; it is _relative_ contemporaneity. + +But it would have been very much better for geology if so loose and +ambiguous a word as "contemporaneous" had been excluded from her +terminology, and if, in its stead, some term expressing similarity of +serial relation, and excluding the notion of time altogether, had been +employed to denote correspondence in position in two or more series of +strata. + +In anatomy, where such correspondence of position has constantly to be +spoken of, it is denoted by the word "homology" and its derivatives; and +for Geology (which after all is only the anatomy and physiology of the +earth) it might be well to invent some single word, such as "homotaxis" +(similarity of order), in order to express an essentially similar idea. +This, however, has not been done, and most probably the inquiry will at +once be made--To what end burden science with a new and strange term in +place of one old, familiar, and part of our common language? + +The reply to this question will become obvious as the inquiry into the +results of palaeontology is pushed further. + +Those whose business it is to acquaint themselves specially with the +works of palaeontologists, in fact, will be fully aware that very few, if +any, would rest satisfied with such a statement of the conclusions of +their branch of biology as that which has just been given. + +Our standard repertories of palaeontology profess to teach us far higher +things--to disclose the entire succession of living forms upon the +surface of the globe; to tell us of a wholly different distribution of +climatic conditions in ancient times; to reveal the character of the +first of all living existences; and to trace out the law of progress from +them to us. + +It may not be unprofitable to bestow on these professions a somewhat more +critical examination than they have hitherto received, in order to +ascertain how far they rest on an irrefragable basis; or whether, after +all, it might not be well for palaeontologists to learn a little more +carefully that scientific "ars artium," the art of saying "I don't know." +And to this end let us define somewhat more exactly the extent of these +pretensions of palaeontology. + +Every one is aware that Professor Bronn's "Untersuchungen" and Professor +Pictet's "Traité de Paléontologie" are works of standard authority, +familiarly consulted by every working palaeontologist. It is desirable to +speak of these excellent books, and of their distinguished authors, with +the utmost respect, and in a tone as far as possible removed from carping +criticism; indeed, if they are specially cited in this place, it is +merely in justification of the assertion that the following propositions, +which may be found implicitly, or explicitly, in the works in question, +are regarded by the mass of palaeontologists and geologists, not only on +the Continent but in this country, as expressing some of the best- +established results of palaeontology. Thus:-- + +Animals and plants began their existence together, not long after the +commencement of the deposition of the sedimentary rocks; and then +succeeded one another, in such a manner, that totally distinct faunae and +florae occupied the whole surface of the earth, one after the other, and +during distinct epochs of time. + +A geological formation is the sum of all the strata deposited over the +whole surface of the earth during one of these epochs: a geological fauna +or flora is the sum of all the species of animals or plants which +occupied the whole surface of the globe, during one of these epochs. + +The population of the earth's surface was at first very similar in all +parts, and only from the middle of the Tertiary epoch onwards, began to +show a distinct distribution in zones. + +The constitution of the original population, as well as the numerical +proportions of its members, indicates a warmer and, on the whole, +somewhat tropical climate, which remained tolerably equable throughout +the year. The subsequent distribution of living beings in zones is the +result of a gradual lowering of the general temperature, which first +began to be felt at the poles. + +It is not now proposed to inquire whether these doctrines are true or +false; but to direct your attention to a much simpler though very +essential preliminary question--What is their logical basis? what are the +fundamental assumptions upon which they all logically depend? and what is +the evidence on which those fundamental propositions demand our assent? + +These assumptions are two: the first, that the commencement of the +geological record is coëval with the commencement of life on the globe; +the second, that geological contemporaneity is the same thing as +chronological synchrony. Without the first of these assumptions there +would of course be no ground for any statement respecting the +commencement of life; without the second, all the other statements cited, +every one of which implies a knowledge of the state of different parts of +the earth at one and the same time, will be no less devoid of +demonstration. + +The first assumption obviously rests entirely on negative evidence. This +is, of course, the only evidence that ever can be available to prove the +commencement of any series of phenomena; but, at the same time, it must +be recollected that the value of negative evidence depends entirely on +the amount of positive corroboration it receives. If A.B. wishes to prove +an _alibi_, it is of no use for him to get a thousand witnesses simply to +swear that they did not see him in such and such a place, unless the +witnesses are prepared to prove that they must have seen him had he been +there. But the evidence that animal life commenced with the Lingula- +flags, _e.g._, would seem to be exactly of this unsatisfactory +uncorroborated sort. The Cambrian witnesses simply swear they "haven't +seen anybody their way"; upon which the counsel for the other side +immediately puts in ten or twelve thousand feet of Devonian sandstones to +make oath they never saw a fish or a mollusk, though all the world knows +there were plenty in their time. + +But then it is urged that, though the Devonian rocks in one part of the +world exhibit no fossils, in another they do, while the lower Cambrian +rocks nowhere exhibit fossils, and hence no living being could have +existed in their epoch. + +To this there are two replies: the first that the observational basis of +the assertion that the lowest rocks are nowhere fossiliferous is an +amazingly small one, seeing how very small an area, in comparison to that +of the whole world, has yet been fully searched; the second, that the +argument is good for nothing unless the unfossiliferous rocks in question +were not only _contemporaneous_ in the geological sense, but +_synchronous_ in the chronological sense. To use the _alibi_ illustration +again. If a man wishes to prove he was in neither of two places, A and B, +on a given day, his witnesses for each place must be prepared to answer +for the whole day. If they can only prove that he was not at A in the +morning, and not at B in the afternoon, the evidence of his absence from +both is nil, because he might have been at B in the morning and at A in +the afternoon. + +Thus everything depends upon the validity of the second assumption. And +we must proceed to inquire what is the real meaning of the word +"contemporaneous" as employed by geologists. To this end a concrete +example may be taken. + +The Lias of England and the Lias of Germany, the Cretaceous rocks of +Britain and the Cretaceous rocks of Southern India, are termed by +geologists "contemporaneous" formations; but whenever any thoughtful +geologist is asked whether he means to say that they were deposited +synchronously, he says, "No,--only within the same great epoch." And if, +in pursuing the inquiry, he is asked what may be the approximate value in +time of a "great epoch"--whether it means a hundred years, or a thousand, +or a million, or ten million years--his reply is, "I cannot tell." + +If the further question be put, whether physical geology is in possession +of any method by which the actual synchrony (or the reverse) of any two +distant deposits can be ascertained, no such method can be heard of; it +being admitted by all the best authorities that neither similarity of +mineral composition, nor of physical character, nor even direct +continuity of stratum, are _absolute_ proofs of the synchronism of even +approximated sedimentary strata: while, for distant deposits, there seems +to be no kind of physical evidence attainable of a nature competent to +decide whether such deposits were formed simultaneously, or whether they +possess any given difference of antiquity. To return to an example +already given: All competent authorities will probably assent to the +proposition that physical geology does not enable us in any way to reply +to this question--Were the British Cretaceous rocks deposited at the same +time as those of India, or are they a million of years younger or a +million of years older? + +Is palaeontology able to succeed where physical geology fails? Standard +writers on palaeontology, as has been seen, assume that she can. They take +it for granted, that deposits containing similar organic remains are +synchronous--at any rate in a broad sense; and yet, those who will study +the eleventh and twelfth chapters of Sir Henry De La Beche's remarkable +"Researches in Theoretical Geology," published now nearly thirty years +ago, and will carry out the arguments there most luminously stated, to +their logical consequences, may very easily convince themselves that even +absolute identity of organic contents is no proof of the synchrony of +deposits, while absolute diversity is no proof of difference of date. Sir +Henry De La Beche goes even further, and adduces conclusive evidence to +show that the different parts of one and the same stratum, having a +similar composition throughout, containing the same organic remains, and +having similar beds above and below it, may yet differ to any conceivable +extent in age. + +Edward Forbes was in the habit of asserting that the similarity of the +organic contents of distant formations was _prima facie_ evidence, not of +their similarity, but of their difference of age; and holding as he did +the doctrine of single specific centres, the conclusion was as legitimate +as any other; for the two districts must have been occupied by migration +from one of the two, or from an intermediate spot, and the chances +against exact coincidence of migration and of imbedding are infinite. + +In point of fact, however, whether the hypothesis of single or of +multiple specific centres be adopted, similarity of organic contents +cannot possibly afford any proof of the synchrony of the deposits which +contain them; on the contrary, it is demonstrably compatible with the +lapse of the most prodigious intervals of time, and with the +interposition of vast changes in the organic and inorganic worlds, +between the epochs in which such deposits were formed. + +On what amount of similarity of their faunae is the doctrine of the +contemporaneity of the European and of the North American Silurians +based? In the last edition of Sir Charles Lyell's "Elementary Geology" it +is stated, on the authority of a former President of this Society, the +late Daniel Sharpe, that between 30 and 40 per cent. of the species of +Silurian Mollusca are common to both sides of the Atlantic. By way of due +allowance for further discovery, let us double the lesser number and +suppose that 60 per cent. of the species are common to the North American +and the British Silurians. Sixty per cent. of species in common is, then, +proof of contemporaneity. + +Now suppose that, a million or two of years hence, when Britain has made +another dip beneath the sea and has come up again, some geologist applies +this doctrine, in comparing the strata laid bare by the upheaval of the +bottom, say, of St. George's Channel with what may then remain of the +Suffolk Crag. Reasoning in the same way, he will at once decide the +Suffolk Crag and the St. George's Channel beds to be contemporaneous; +although we happen to know that a vast period (even in the geological +sense) of time, and physical changes of almost unprecedented extent, +separate the two. But if it be a demonstrable fact that strata +containing more than 60 or 70 per cent. of species of Mollusca in common, +and comparatively close together, may yet be separated by an amount of +geological time sufficient to allow of some of the greatest physical +changes the world has seen, what becomes of that sort of contemporaneity +the sole evidence of which is a similarity of facies, or the identity of +half a dozen species, or of a good many genera? + +And yet there is no better evidence for the contemporaneity assumed by +all who adopt the hypothesis of universal faunae and florae, of a +universally uniform climate, and of a sensible cooling of the globe +during geological time. + +There seems, then, no escape from the admission that neither physical +geology, nor palaeontology, possesses any method by which the absolute +synchronism of two strata can be demonstrated. All that geology can prove +is local order of succession. It is mathematically certain that, in any +given vertical linear section of an undisturbed series of sedimentary +deposits, the bed which lies lowest is the oldest. In many other vertical +linear sections of the same series, of course, corresponding beds will +occur in a similar order; but, however great may be the probability, no +man can say with absolute certainty that the beds in the two sections +were synchronously deposited. For areas of moderate extent, it is +doubtless true that no practical evil is likely to result from assuming +the corresponding beds to be synchronous or strictly contemporaneous; and +there are multitudes of accessory circumstances which may fully justify +the assumption of such synchrony. But the moment the geologist has to +deal with large areas, or with completely separated deposits, the +mischief of confounding that "homotaxis" or "similarity of arrangement," +which _can_ be demonstrated, with "synchrony" or "identity of date," for +which there is not a shadow of proof, under the one common term of +"contemporaneity" becomes incalculable, and proves the constant source of +gratuitous speculations. + +For anything that geology or palaeontology are able to show to the +contrary, a Devonian fauna and flora in the British Islands may have been +contemporaneous with Silurian life in North America, and with a +Carboniferous fauna and flora in Africa. Geographical provinces and zones +may have been as distinctly marked in the Palaeozoic epoch as at present, +and those seemingly sudden appearances of new genera and species, which +we ascribe to new creation, may be simple results of migration. + +It may be so; it may be otherwise. In the present condition of our +knowledge and of our methods, one verdict--"not proven, and not +provable"--must be recorded against all the grand hypotheses of the +palaeontologist respecting the general succession of life on the globe. +The order and nature of terrestrial life, as a whole, are open questions. +Geology at present provides us with most valuable topographical records, +but she has not the means of working them into a universal history. Is +such a universal history, then, to be regarded as unattainable? Are all +the grandest and most interesting problems which offer themselves to the +geological student, essentially insoluble? Is he in the position of a +scientific Tantalus--doomed always to thirst for a knowledge which he +cannot obtain? The reverse is to be hoped; nay, it may not be impossible +to indicate the source whence help will come. + +In commencing these remarks, mention was made of the great obligations +under which the naturalist lies to the geologist and palaeontologist. +Assuredly the time will come when these obligations will be repaid +tenfold, and when the maze of the world's past history, through which the +pure geologist and the pure palaeontologist find no guidance, will be +securely threaded by the clue furnished by the naturalist. + +All who are competent to express an opinion on the subject are, at +present, agreed that the manifold varieties of animal and vegetable form +have not either come into existence by chance, nor result from capricious +exertions of creative power; but that they have taken place in a definite +order, the statement of which order is what men of science term a natural +law. Whether such a law is to be regarded as an expression of the mode of +operation of natural forces, or whether it is simply a statement of the +manner in which a supernatural power has thought fit to act, is a +secondary question, so long as the existence of the law and the +possibility of its discovery by the human intellect are granted. But he +must be a half-hearted philosopher who, believing in that possibility, +and having watched the gigantic strides of the biological sciences during +the last twenty years, doubts that science will sooner or later make this +further step, so as to become possessed of the law of evolution of +organic forms--of the unvarying order of that great chain of causes and +effects of which all organic forms, ancient and modern, are the links. +And then, if ever, we shall be able to begin to discuss, with profit, the +questions respecting the commencement of life, and the nature of the +successive populations of the globe, which so many seem to think are +already answered. + +The preceding arguments make no particular claim to novelty; indeed they +have been floating more or less distinctly before the minds of geologists +for the last thirty years; and if, at the present time, it has seemed +desirable to give them more definite and systematic expression, it is +because palaeontology is every day assuming a greater importance, and now +requires to rest on a basis the firmness of which is thoroughly well +assured. Among its fundamental conceptions, there must be no confusion +between what is certain and what is more or less probable.[1] But, +pending the construction of a surer foundation than palaeontology now +possesses, it may be instructive, assuming for the nonce the general +correctness of the ordinary hypothesis of geological contemporaneity, to +consider whether the deductions which are ordinarily drawn from the whole +body of palaeontological facts are justifiable. + +[Footnote 1: "Le plus grand service qu'on puisse rendre à la science est +d'y faire place nette avant d'y rien construire."--CUVIER.] + +The evidence on which such conclusions are based is of two kinds, +negative and positive. The value of negative evidence, in connection with +this inquiry, has been so fully and clearly discussed in an address from +the chair of this Society,[2] which none of us have forgotten, that +nothing need at present be said about it; the more, as the considerations +which have been laid before you have certainly not tended to increase +your estimation of such evidence. It will be preferable to turn to the +positive facts of palaeontology, and to inquire what they tell us. + +[Footnote 2: Anniversary Address for 1851, _Quart. Journ. Geol. Soc._ +vol. vii.] + +We are all accustomed to speak of the number and the extent of the +changes in the living population of the globe during geological time as +something enormous: and indeed they are so, if we regard only the +negative differences which separate the older rocks from the more modern, +and if we look upon specific and generic changes as great changes, which +from one point of view, they truly are. But leaving the negative +differences out of consideration, and looking only at the positive data +furnished by the fossil world from a broader point of view--from that of +the comparative anatomist who has made the study of the greater +modifications of animal form his chief business--a surprise of another +kind dawns upon the mind; and under _this_ aspect the smallness of the +total change becomes as astonishing as was its greatness under the other. + +There are two hundred known orders of plants; of these not one is +certainly known to exist exclusively in the fossil state. The whole lapse +of geological time has as yet yielded not a single new ordinal type of +vegetable structure.[3] + +[Footnote 3: See Hooker's _Introductory Essay to the Flora of Tasmania_, +p. xxiii.] + +The positive change in passing from the recent to the ancient animal +world is greater, but still singularly small. No fossil animal is so +distinct from those now living as to require to be arranged even in a +separate class from those which contain existing forms. It is only when +we come to the orders, which may be roughly estimated at about a hundred +and thirty, that we meet with fossil animals so distinct from those now +living as to require orders for themselves; and these do not amount, on +the most liberal estimate, to more than about 10 per cent. of the whole. + +There is no certainly known extinct order of Protozoa; there is but one +among the Coelenterata--that of the rugose corals; there is none among +the Mollusca; there are three, the Cystidea, Blastoidea, and +Edrioasterida, among the Echinoderms; and two, the Trilobita and +Eurypterida, among the Crustacea; making altogether five for the great +sub-kingdom of Annulosa. Among Vertebrates there is no ordinally distinct +fossil fish: there is only one extinct order of Amphibia--the +Labyrinthodonts; but there are at least four distinct orders of Reptilia, +viz. the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, and +perhaps another or two. There is no known extinct order of Birds, and no +certainly known extinct order of Mammals, the ordinal distinctness of the +"Toxodontia" being doubtful. + +The objection that broad statements of this kind, after all, rest largely +on negative evidence is obvious, but it has less force than may at first +be supposed; for, as might be expected from the circumstances of the +case, we possess more abundant positive evidence regarding Fishes and +marine Mollusks than respecting any other forms of animal life; and yet +these offer us, through the whole range of geological time, no species +ordinally distinct from those now living; while the far less numerous +class of Echinoderms presents three, and the Crustacea two, such orders, +though none of these come down later than the Palaeozoic age. Lastly, the +Reptilia present the extraordinary and exceptional phenomenon of as many +extinct as existing orders, if not more; the four mentioned maintaining +their existence from the Lias to the Chalk inclusive. + +Some years ago one of your Secretaries pointed out another kind of +positive palaeontological evidence tending towards the same conclusion-- +afforded by the existence of what he termed "persistent types" of +vegetable and of animal life.[4] He stated, on the authority of Dr. +Hooker, that there are Carboniferous plants which appear to be +generically identical with some now living; that the cone of the Oolitic +_Araucaria_ is hardly distinguishable from that of an existing species; +that a true _Pinus_ appears in the Purbecks and a _Juglans_ in the Chalk; +while, from the Bagshot Sands, a _Banksia_, the wood of which is not +distinguishable from that of species now living in Australia, had been +obtained. + +[Footnote 4: See the abstract of a Lecture "On the Persistent Types of +Animal Life," in the _Notices of the Meetings of the Royal Institution of +Great Britain_.--June 3, 1859, vol. iii. p. 151.] + +Turning to the animal kingdom, he affirmed the tabulate corals of the +Silurian rocks to be wonderfully like those which now exist; while even +the families of the Aporosa were all represented in the older Mesozoic +rocks. + +Among the Mollusca similar facts were adduced. Let it be borne in mind +that _Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina, +Orbicula, Lingula, Rhynchonclla_, and _Nautilus_, all of which are +existing _genera_, are given without a doubt as Silurian in the last +edition of "Siluria"; while the highest forms of the highest Cephalopods +are represented in the Lias by a genus _Belemnoteuthis_, which presents +the closest relation to the existing _Loligo_. + +The two highest groups of the Annulosa, the Insecta and the Arachnida, +are represented in the Coal, either by existing genera, or by forms +differing from existing genera in quite minor peculiarities. + +Turning to the Vertebrata, the only palaeozoic Elasmobranch Fish of which +we have any complete knowledge is the Devonian and Carboniferous +_Pleuracanthus_, which differs no more from existing Sharks than these do +from one another. + +Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and +great as is their range in time, a large mass of evidence has recently +been adduced to show that almost all those respecting which we possess +sufficient information, are referable to the same sub-ordinal groups as +the existing _Lepidosteus, Polypterus_, and Sturgeon; and that a singular +relation obtains between the older and the younger Fishes; the former, +the Devonian Ganoids, being almost all members of the same sub-order as +_Polypterus_, while the Mesozoic Ganoids are almost all similarly allied +to _Lepidosteus_.[5] + +[Footnote 5: "Memoirs of the Geological Survey of the United Kingdom.-- +Decade x. Preliminary Essay upon the Systematic Arrangement of the Fishes +of the Devonian Epoch."] + +Again, what can be more remarkable than the singular constancy of +structure preserved throughout a vast period of time by the family of the +Pycnodonts and by that of the true Coelacanths; the former persisting, +with but insignificant modifications, from the Carboniferous to the +Tertiary rocks, inclusive; the latter existing, with still less change, +from the Carboniferous rocks to the Chalk, inclusive? + +Among Reptiles, the highest living group, that of the Crocodilia, is +represented, at the early part of the Mesozoic epoch, by species +identical in the essential characters of their organisation with those +now living, and differing from the latter only in such matters as the +form of the articular facets of the vertebral centra, in the extent to +which the nasal passages are separated from the cavity of the mouth by +bone, and in the proportions of the limbs. + +And even as regards the Mammalia, the scanty remains of Triassic and +Oolitic species afford no foundation for the supposition that the +organisation of the oldest forms differed nearly so much from some of +those which now live as these differ from one another. + +It is needless to multiply these instances; enough has been said to +justify the statement that, in view of the immense diversity of known +animal and vegetable forms, and the enormous lapse of time indicated by +the accumulation of fossiliferous strata, the only circumstance to be +wondered at is, not that the changes of life, as exhibited by positive +evidence, have been so great but that they have been so small. + +Be they great or small, however, it is desirable to attempt to estimate +them. Let us, therefore, take each great division of the animal world in +succession, and, whenever an order or a family can be shown to have had a +prolonged existence, let us endeavour to ascertain how far the later +members of the group differ from the earlier ones. If these later +members, in all or in many cases, exhibit a certain amount of +modification, the fact is, so far, evidence in favour of a general law of +change; and, in a rough way, the rapidity of that change will be measured +by the demonstrable amount of modification. On the other hand, it must be +recollected that the absence of any modification, while it may leave the +doctrine of the existence of a law of change without positive support, +cannot possibly disprove all forms of that doctrine, though it may afford +a sufficient refutation of many of them. + +The PROTOZOA.--The Protozoa are represented throughout the whole range of +geological series, from the Lower Silurian formation to the present day. +The most ancient forms recently made known by Ehrenberg are exceedingly +like those which now exist: no one has ever pretended that the difference +between any ancient and any modern Foraminifera is of more than generic +value, nor are the oldest Foraminifera either simpler, more embryonic, or +less differentiated, than the existing forms. + +The COELENTERATA.--The Tabulate Corals have existed from the Silurian +epoch to the present day, but I am not aware that the ancient +_Heliolites_ possesses a single mark of a more embryonic or less +differentiated character, or less high organisation, than the existing +_Heliopora_. As for the Aporose Corals, in what respect is the Silurian +_Paloeocyclus_ less highly organised or more embryonic than the modern +_Fungia_, or the Liassic Aporosa than the existing members of the same +families? + +The _Mollusca_--In what sense is the living _Waldheimia_ less embryonic, +or more specialised, than the palaeozoic _Spirifer_; or the existing +_Rhynchonelloe, Cranioe, Discinoe, Linguloe_, than the Silurian species +of the same genera? In what sense can _Loligo_ or _Spirula_ be said to be +more specialised, or less embryonic, than _Belemnites_; or the modern +species of Lamellibranch and Gasteropod genera, than the Silurian species +of the same genera? + +The ANNULOSA.--The Carboniferous Insecta and Arachnida are neither less +specialised, nor more embryonic, than these that now live, nor are the +Liassic Cirripedia and Macrura; while several of the Brachyura, which +appear in the Chalk, belong to existing genera; and none exhibit either +an intermediate, or an embryonic, character. + +The VERTEBRATA.--Among fishes I have referred to the Coelacanthini +(comprising the genera _Coelacanthus, Holophagus, Undina_, and +_Macropoma_) as affording an example of a persistent type; and it is most +remarkable to note the smallness of the differences between any of these +fishes (affecting at most the proportions of the body and fins, and the +character and sculpture of the scales), notwithstanding their enormous +range in time. In all the essentials of its very peculiar structure, the +_Macropoma_ of the Chalk is identical with the _Coelacanthus_ of the +Coal. Look at the genus _Lepidotus_, again, persisting without a +modification of importance from the Liassic to the Eocene formations +inclusively. + +Or among the Teleostei--in what respect is the _Beryx_ of the Chalk more +embryonic, or less differentiated, than _Beryx lineatus_ of King George's +Sound? + +Or to turn to the higher Vertebrata--in what sense are the Liassic +Chelonia inferior to those which now exist? How are the Cretaceous +Ichthyosauria, Plesiosauria, or Pterosauria less embryonic, or more +differentiated, species than those of the Lias? + +Or lastly, in what circumstance is the _Phascolotherium_ more embryonic, +or of a more generalised type, than the modern Opossum; or a _Lophiodon_, +or a _Paloeotherium_, than a modern _Tapirus_ or _Hyrax_? + +These examples might be almost indefinitely multiplied, but surely they +are sufficient to prove that the only safe and unquestionable testimony +we can procure--positive evidence--fails to demonstrate any sort of +progressive modification towards a less embryonic, or less generalised, +type in a great many groups of animals of long-continued geological +existence. In these groups there is abundant evidence of variation--none +of what is ordinarily understood as progression; and, if the known +geological record is to be regarded as even any considerable fragment of +the whole, it is inconceivable that any theory of a necessarily +progressive development can stand, for the numerous orders and families +cited afford no trace of such a process. + +But it is a most remarkable fact, that, while the groups which have been +mentioned, and many besides, exhibit no sign of progressive modification, +there are others, co-existing with them, under the same conditions, in +which more or less distinct indications of such a process seems to be +traceable. Among such indications I may remind you of the predominance of +Holostome Gasteropoda in the older rocks as compared with that of +Siphonostone Gasteropoda in the later. A case less open to the objection +of negative evidence, however, is that afforded by the Tetrabranchiate +Cephalopoda, the forms of the shells and of the septal sutures exhibiting +a certain increase of complexity in the newer genera. Here, however, one +is met at once with the occurrence of _Orthoceras_ and _Baculites_ at the +two ends of the series, and of the fact that one of the simplest genera, +_Nautilus_, is that which now exists. + +The Crinoidea, in the abundance of stalked forms in the ancient +formations as compared with their present rarity, seem to present us with +a fair case of modification from a more embryonic towards a less +embryonic condition. But then, on careful consideration of the facts, the +objection arises that the stalk, calyx, and arms of the palaeozoic Crinoid +are exceedingly different from the corresponding organs of a larval +_Comatula_; and it might with perfect justice be argued that +_Actinocrinus_ and _Eucalyptocrinus_, for example, depart to the full as +widely, in one direction, from the stalked embryo of _Comatula_, as +_Comatula_ itself does in the other. + +The Echinidea, again, are frequently quoted as exhibiting a gradual +passage from a more generalised to a more specialised type, seeing that +the elongated, or oval, Spatangoids appear after the spheroidal +Echinoids. But here it might be argued, on the other hand, that the +spheroidal Echinoids, in reality, depart further from the general plan +and from the embryonic form than the elongated Spatangoids do; and that +the peculiar dental apparatus and the pedicellariae of the former are +marks of at least as great differentiation as the petaloid ambulacra and +semitae of the latter. + +Once more, the prevalence of Macrurous before Brachyurous Podophthalmia +is, apparently, a fair piece of evidence in favour of progressive +modification in the same order of Crustacea; and yet the case will not +stand much sifting, seeing that the Macrurous Podophthalmia depart as far +in one direction from the common type of Podophthalmia, or from any +embryonic condition of the Brachyura, as the Brachyura do in the other; +and that the middle terms between Macrura and Brachyura--the Anomura--are +little better represented in the older Mesozoic rocks than the Brachyura +are. + +None of the cases of progressive modification which are cited from among +the Invertebrata appear to me to have a foundation less open to criticism +than these; and if this be so, no careful reasoner would, I think, be +inclined to lay very great stress upon them. Among the Vertebrata, +however, there are a few examples which appear to be far less open to +objection. + +It is, in fact, true of several groups of Vertebrata which have lived +through a considerable range of time, that the endoskeleton (more +particularly the spinal column) of the older genera presents a less +ossified, and, so far, less differentiated, condition than that of the +younger genera. Thus the Devonian Ganoids, though almost all members of +the same sub-order as _Polypterus_, and presenting numerous important +resemblances to the existing genus, which possesses biconclave vertebrae, +are, for the most part, wholly devoid of ossified vertebral centra. The +Mesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, while +the existing _Lepidosteus_ has Salamandroid, opisthocoelous, vertebrae. +So, none of the Palaeozoic Sharks have shown themselves to be possessed of +ossified vertebrae, while the majority of modern Sharks possess such +vertebrae. Again, the more ancient Crocodilia and Lacertilia have vertebrae +with the articular facets of their centra flattened or biconcave, while +the modern members of the same group have them procoelous. But the most +remarkable examples of progressive modification of the vertebral column, +in correspondence with geological age, are those afforded by the +Pycnodonts among fish, and the Labyrinthodonts among Amphibia. + +The late able ichthyologist Heckel pointed out the fact, that, while the +Pycnodonts never possess true vertebral centra, they differ in the degree +of expansion and extension of the ends of the bony arches of the vertebrae +upon the sheath of the notochord; the Carboniferous forms exhibiting +hardly any such expansion, while the Mesozoic genera present a greater +and greater development, until, in the Tertiary forms, the expanded ends +become suturally united so as to form a sort of false vertebra. Hermann +von Meyer, again, to whose luminous researches we are indebted for our +present large knowledge of the organisation of the older Labyrinthodonts, +has proved that the Carboniferous _Archegosaurus_ had very imperfectly +developed vertebral centra, while the Triassic _Mastodonsaurus_ had the +same parts completely ossified.[6] + +[Footnote 6: As this Address is passing through the press (March 7, +1862), evidence lies before me of the existence of a new Labyrinthodont +(_Pholidogaster_), from the Edinburgh coal-field with well-ossified +vertebral centra.] + +The regularity and evenness of the dentition of the _Anoplotherium_, as +contrasted with that of existing Artiodactyles, and the assumed nearer +approach of the dentition of certain ancient Carnivores to the typical +arrangement, have also been cited as exemplifications of a law of +progressive development, but I know of no other cases based on positive +evidence which are worthy of particular notice. + +What then does an impartial survey of the positively ascertained truths +of palaeontology testify in relation to the common doctrines of +progressive modification, which suppose that modification to have taken +place by a necessary progress from more to less embryonic forms, or from +more to less generalised types, within the limits of the period +represented by the fossiliferous rocks? + +It negatives those doctrines; for it either shows us no evidence of any +such modification, or demonstrates it to have been very slight; and as to +the nature of that modification, it yields no evidence whatsoever that +the earlier members of any long-continued group were more generalised in +structure than the later ones. To a certain extent, indeed, it may be +said that imperfect ossification of the vertebral column is an embryonic +character; but, on the other hand, it would be extremely incorrect to +suppose that the vertebral columns of the older Vertebrata are in any +sense embryonic in their whole structure. + +Obviously, if the earliest fossiliferous rocks now known are coëval with +the commencement of life, and if their contents give us any just +conception of the nature and the extent of the earliest fauna and flora, +the insignificant amount of modification which can be demonstrated to +have taken place in any one group of animals, or plants, is quite +incompatible with the hypothesis that all living forms are the results of +a necessary process of progressive development, entirely comprised within +the time represented by the fossiliferous rocks. + +Contrariwise, any admissible hypothesis of progressive modification must +be compatible with persistence without progression, through indefinite +periods. And should such an hypothesis eventually be proved to be true, +in the only way in which it can be demonstrated, viz. by observation and +experiment upon the existing forms of life, the conclusion will +inevitably present itself, that the Palaeozoic Mesozoic, and Cainozoic +faunae and florae, taken together, bear somewhat the same proportion to the +whole series of living beings which have occupied this globe, as the +existing fauna and flora do to them. + +Such are the results of palaeontology as they appear, and have for some +years appeared, to the mind of an inquirer who regards that study simply +as one of the applications of the great biological sciences, and who +desires to see it placed upon the same sound basis as other branches of +physical inquiry. If the arguments which have been brought forward are +valid, probably no one, in view of the present state of opinion, will be +inclined to think the time wasted which has been spent upon their +elaboration. + + + +X + + +GEOLOGICAL REFORM + +[1869] + +"A great reform in geological speculation seems now to have become +necessary." + +"It is quite certain that a great mistake has been made--that British +popular geology at the present time is in direct opposition to the +principles of Natural Philosophy."[1] + +[Footnote 1: On Geological Time. By Sir W. Thomson, LL.D. _Transactions +of the Geological Society of Glasgow_, vol. iii.] + +In reviewing the course of geological thought during the past year, for +the purpose of discovering those matters to which I might most fitly +direct your attention in the Address which it now becomes my duty to +deliver from the Presidential Chair, the two somewhat alarming sentences +which I have just read, and which occur in an able and interesting essay +by an eminent natural philosopher, rose into such prominence before my +mind that they eclipsed everything else. + +It surely is a matter of paramount importance for the British geologists +(some of them very popular geologists too) here in solemn annual session +assembled, to inquire whether the severe judgment thus passed upon them +by so high an authority as Sir William Thomson is one to which they must +plead guilty _sans phrase_, or whether they are prepared to say "not +guilty," and appeal for a reversal of the sentence to that higher court +of educated scientific opinion to which we are all amenable. + +As your attorney-general for the time being, I thought I could not do +better than get up the case with a view of advising you. It is true that +the charges brought forward by the other side involve the consideration +of matters quite foreign to the pursuits with which I am ordinarily +occupied; but, in that respect, I am only in the position which is, nine +times out of ten, occupied by counsel, who nevertheless contrive to gain +their causes, mainly by force of mother-wit and common-sense, aided by +some training in other intellectual exercises. + +Nerved by such precedents, I proceed to put my pleading before you. + +And the first question with which I propose to deal is, What is it to +which Sir W. Thomson refers when he speaks of "geological speculation" +and "British popular geology"? + +I find three, more or less contradictory, systems of geological thought, +each of which might fairly enough claim these appellations, standing side +by side in Britain. I shall call one of them CATASTROPHISM, another +UNIFORMITARIANISM, the third EVOLUTIONISM; and I shall try briefly to +sketch the characters of each, that you may say whether the +classification is, or is not, exhaustive. + +By CATASTROPHISM, I mean any form of geological speculation which, in +order to account for the phenomena of geology, supposes the operation of +forces different in their nature, or immeasurably different in power, +from those which we at present see in action in the universe. + +The Mosaic cosmogony is, in this sense, catastrophic, because it assumes +the operation of extra-natural power. The doctrine of violent upheavals, +_débâcles_, and cataclysms in general, is catastrophic, so far as it +assumes that these were brought about by causes which have now no +parallel. There was a time when catastrophism might, pre-eminently, have +claimed the title of "British popular geology"; and assuredly it has yet +many adherents, and reckons among its supporters some of the most +honoured members of this Society. + +By UNIFORMITARIANISM, I mean especially, the teaching of Hutton and of +Lyell. + +That great though incomplete work, "The Theory of the Earth," seems to me +to be one of the most remarkable contributions to geology which is +recorded in the annals of the science. So far as the not-living world is +concerned, uniformitarianism lies there, not only in germ, but in blossom +and fruit. + +If one asks how it is that Hutton was led to entertain views so far in +advance of those prevalent in his time, in some respects; while, in +others, they seem almost curiously limited, the answer appears to me to +be plain. + +Hutton was in advance of the geological speculation of his time, because, +in the first place, he had amassed a vast store of knowledge of the facts +of geology, gathered by personal observation in travels of considerable +extent; and because, in the second place, he was thoroughly trained in +the physical and chemical science of his day, and thus possessed, as much +as any one in his time could possess it, the knowledge which is requisite +for the just interpretation of geological phenomena, and the habit of +thought which fits a man for scientific inquiry. + +It is to this thorough scientific training that I ascribe Hutton's steady +and persistent refusal to look to other causes than those now in +operation, for the explanation of geological phenomena. + +Thus he writes:--"I do not pretend, as he [M. de Luc] does in his theory, +to describe the beginning of things. I take things such as I find them at +present; and from these I reason with regard to that which must have +been."[2] + +[Footnote 2: _The Theory of the Earth_, vol. i. p. 173, note.] + +And again:--"A theory of the earth, which has for object truth, can have +no retrospect to that which had preceded the present order of the world; +for this order alone is what we have to reason upon; and to reason +without data is nothing but delusion. A theory, therefore, which is +limited to the actual constitution of this earth cannot be allowed to +proceed one step beyond the present order of things."[3] + +[Footnote 3: _Ibid._, vol. i. p. 281.] + +And so clear is he, that no causes beside such as are now in operation +are needed to account for the character and disposition of the components +of the crust of the earth, that he says, broadly and boldly:--" ... There +is no part of the earth which has not had the same origin, so far as this +consists in that earth being collected at the bottom of the sea, and +afterwards produced, as land, along with masses of melted substances, by +the operation of mineral causes."[4] + +[Footnote 4: _Ibid._. p. 371.] + +But other influences were at work upon Hutton beside those of a mind +logical by nature, and scientific by sound training; and the peculiar +turn which his speculations took seems to me to be unintelligible, unless +these be taken into account. The arguments of the French astronomers and +mathematicians, which, at the end of the last century, were held to +demonstrate the existence of a compensating arrangement among the +celestial bodies, whereby all perturbations eventually reduced themselves +to oscillations on each side of a mean position, and the stability of the +solar system was secured, had evidently taken strong hold of Hutton's +mind. + +In those oddly constructed periods which seem to have prejudiced many +persons against reading his works, but which are full of that peculiar, +if unattractive, eloquence which flows from mastery of the subject, +Hutton says:-- + +"We have now got to the end of our reasoning; we have no data further to +conclude immediately from that which actually is. But we have got enough; +we have the satisfaction to find, that in Nature there is wisdom, system, +and consistency. For having, in the natural history of this earth, seen a +succession of worlds, we may from this conclude that there is a system in +Nature; in like manner as, from seeing revolutions of the planets, it is +concluded, that there is a system by which they are intended to continue +those revolutions. But if the succession of worlds is established in the +system of nature, it is in vain to look for anything higher in the origin +of the earth. The result, therefore, of this physical inquiry is, that we +find no vestige of a beginning,--no prospect of an end."[5] + +[Footnote 5: _Ibid._, vol. i. p. 200.] + +Yet another influence worked strongly upon Hutton. Like most philosophers +of his age, he coquetted with those final causes which have been named +barren virgins, but which might be more fitly termed the _hetairoe_ of +philosophy, so constantly have they led men astray. The final cause of +the existence of the world is, for Hutton, the production of life and +intelligence. + +"We have now considered the globe of this earth as a machine, constructed +upon chemical as well as mechanical principles, by which its different +parts are all adapted, in form, in quality, and in quantity, to a certain +end; an end attained with certainty or success; and an end from which we +may perceive wisdom, in contemplating the means employed. + +"But is this world to be considered thus merely as a machine, to last no +longer than its parts retain their present position, their proper forms +and qualities? Or may it not be also considered as an organised body? +such as has a constitution in which the necessary decay of the machine is +naturally repaired, in the exertion of those productive powers by which +it had been formed. + +"This is the view in which we are now to examine the globe; to see if +there be, in the constitution of this world, a reproductive operation, by +which a ruined constitution may be again repaired, and a duration or +stability thus procured to the machine, considered as a world sustaining +plants and animals."[6] + +[Footnote 6: _Ibid._, vol. i. pp. 16, 17.] + +Kirwan, and the other Philistines of the day, accused Hutton of declaring +that his theory implied that the world never had a beginning, and never +differed in condition from its present state. Nothing could be more +grossly unjust, as he expressly guards himself against any such +conclusion in the following terms:-- + +"But in thus tracing back the natural operations which have succeeded +each other, and mark to us the course of time past, we come to a period +in which we cannot see any farther. This, however, is not the beginning +of the operations which proceed in time and according to the wise economy +of this world; nor is it the establishing of that which, in the course of +time, had no beginning; it is only the limit of our retrospective view of +those operations which have come to pass in time, and have been conducted +by supreme intelligence."[7] + +[Footnote 7: _Ibid._, vol. i. p. 223.] + +I have spoken of Uniformitarianism as the doctrine of Hutton and of +Lyell. If I have quoted the older writer rather than the newer, it is +because his works are little known, and his claims on our veneration too +frequently forgotten, not because I desire to dim the fame of his eminent +successor. Few of the present generation of geologists have read +Playfair's "Illustrations," fewer still the original "Theory of the +Earth"; the more is the pity; but which of us has not thumbed every page +of the "Principles of Geology"? I think that he who writes fairly the +history of his own progress in geological thought, will not be able to +separate his debt to Hutton from his obligations to Lyell; and the +history of the progress of individual geologists is the history of +geology. + + +No one can doubt that the influence of uniformitarian views has been +enormous, and, in the main, most beneficial and favourable to the +progress of sound geology. + +Nor can it be questioned that Uniformitarianism has even a stronger title +than Catastrophism to call itself the geological speculation of Britain, +or, if you will, British popular geology. For it is eminently a British +doctrine, and has even now made comparatively little progress on the +continent of Europe. Nevertheless, it seems to me to be open to serious +criticism upon one of its aspects. + +I have shown how unjust was the insinuation that Hutton denied a +beginning to the world. But it would not be unjust to say that he +persistently in practice, shut his eyes to the existence of that prior +and different state of things which, in theory, he admitted; and, in this +aversion to look beyond the veil of stratified rocks, Lyell follows him. + +Hutton and Lyell alike agree in their indisposition to carry their +speculations a step beyond the period recorded in the most ancient strata +now open to observation in the crust of the earth. This is, for Hutton, +"the point in which we cannot see any farther"; while Lyell tells us,-- + +"The astronomer may find good reasons for ascribing the earth's form to +the original fluidity of the mass, in times long antecedent to the first +introduction of living beings into the planet; but the geologist must be +content to regard the earliest monuments which it is his task to +interpret, as belonging to a period when the crust had already acquired +great solidity and thickness, probably as great as it now possesses, and +when volcanic rocks, not essentially differing from those now produced, +were formed from time to time, the intensity of volcanic heat being +neither greater nor less than it is now."[8] + +[Footnote 8: _Principles of Geology_, vol. ii. p. 211.] + +And again, "As geologists, we learn that it is not only the present +condition of the globe which has been suited to the accommodation of +myriads of living creatures, but that many former states also have been +adapted to the organisation and habits of prior races of beings. The +disposition of the seas, continents and islands, and the climates, have +varied; the species likewise have been changed; and yet they have all +been so modelled, on types analogous to those of existing plants and +animals, as to indicate, throughout, a perfect harmony of design and +unity of purpose. To assume that the evidence of the beginning, or end, +of so vast a scheme lies within the reach of our philosophical inquiries, +or even of our speculations, appears to be inconsistent with a just +estimate of the relations which subsist between the finite powers of man +and the attributes of an infinite and eternal Being."[9] + +[Footnote 9: _Ibid._, vol. ii. p. 613.] + +The limitations implied in these passages appear to me to constitute the +weakness and the logical defect of Uniformitarianism. No one will impute +blame to Hutton that, in face of the imperfect condition, in his day, of +those physical sciences which furnish the keys to the riddles of geology, +he should have thought it practical wisdom to limit his theory to an +attempt to account for "the present order of things"; but I am at a loss +to comprehend why, for all time, the geologist must be content to regard +the oldest fossiliferous rocks as the _ultima Thule_ of his science; or +what there is inconsistent with the relations between the finite and the +infinite mind, in the assumption, that we may discern somewhat of the +beginning, or of the end, of this speck in space we call our earth. The +finite mind is certainly competent to trace out the development of the +fowl within the egg; and I know not on what ground it should find more +difficulty in unravelling the complexities Of the development of the +earth. In fact, as Kant has well remarked,[10] the cosmical process is +really simpler than the biological. + +[Footnote 10: "Man darf es sich also nicht befremden lassen, wenn ich +mich unterstehe zu sagen, dass eher die Bildung aller Himmelskörper, die +Ursache ihrer Bewegungen, kurz der Ursprung der gantzen gegenwärtigen +Verfassung des Weltbaues werden können eingesehen werden, ehe die +Erzeugung eines einzigen Krautes oder einer Raupe aus mechanischen +Gründen, deutlich und vollständig kund werden wird."--KANT'S _Sämmtliche +Werke_, Bd. i. p. 220.] + +This attempt to limit, at a particular point, the progress of inductive +and deductive reasoning from the things which are, to those which were-- +this faithlessness to its own logic, seems to me to have cost +Uniformitarianism the place, as the permanent form of geological +speculation, which it might otherwise have held. + +It remains that I should put before you what I understand to be the third +phase of geological speculation--namely, EVOLUTIONISM. + +I shall not make what I have to say on this head clear, unless I diverge, +or seem to diverge, for a while, from the direct path of my discourse, so +far as to explain what I take to be the scope of geology itself. I +conceive geology to be the history of the earth, in precisely the same +sense as biology is the history of living beings; and I trust you will +not think that I am overpowered by the influence of a dominant pursuit if +I say that I trace a close analogy between these two histories. + +If I study a living being, under what heads does the knowledge I obtain +fall? I can learn its structure, or what we call its ANATOMY; and its +DEVELOPMENT, or the series of changes which it passes through to acquire +its complete structure. Then I find that the living being has certain +powers resulting from its own activities, and the interaction of these +with the activities of other things--the knowledge of which is +PHYSIOLOGY. Beyond this the living being has a position in space and +time, which is its DISTRIBUTION. All these form the body of ascertainable +facts which constitute the _status quo_ of the living creature. But these +facts have their causes; and the ascertainment of these causes is the +doctrine of AETIOLOGY. + +If we consider what is knowable about the earth, we shall find that such +earth-knowledge--if I may so translate the word geology--falls into the +same categories. + +What is termed stratigraphical geology is neither more nor less than the +anatomy of the earth; and the history of the succession of the formations +is the history of a succession of such anatomies, or corresponds with +development, as distinct from generation. + +The internal heat of the earth, the elevation and depression of its +crust, its belchings forth of vapours, ashes, and lava, are its +activities, in as strict a sense as are warmth and the movements and +products of respiration the activities of an animal. The phenomena of the +seasons, of the trade winds, of the Gulf-stream, are as much the results +of the reaction between these inner activities and outward forces, as are +the budding of the leaves in spring and their falling in autumn the +effects of the interaction between the organisation of a plant and the +solar light and heat. And, as the study of the activities of the living +being is called its physiology, so are these phenomena the subject-matter +of an analogous telluric physiology, to which we sometimes give the name +of meteorology, sometimes that of physical geography, sometimes that of +geology. Again, the earth has a place in space and in time, and relations +to other bodies in both these respects, which constitute its +distribution. This subject is usually left to the astronomer; but a +knowledge of its broad outlines seems to me to be an essential +constituent of the stock of geological ideas. + +All that can be ascertained concerning the structure, succession of +conditions, actions, and position in space of the earth, is the matter of +fact of its natural history. But, as in biology, there remains the matter +of reasoning from these facts to their causes, which is just as much +science as the other, and indeed more; and this constitutes geological +aetiology. + +Having regard to this general scheme of geological knowledge and thought, +it is obvious that geological speculation may be, so to speak, anatomical +and developmental speculation, so far as it relates to points of +stratigraphical arrangement which are out of reach of direct observation; +or, it may be physiological speculation so far as it relates to +undetermined problems relative to the activities of the earth; or, it may +be distributional speculation, if it deals with modifications of the +earth's place in space; or, finally, it will be aetiological speculation +if it attempts to deduce the history of the world, as a whole, from the +known properties of the matter of the earth, in the conditions in which +the earth has been placed. + +For the purposes of the present discourse I may take this last to be what +is meant by "geological speculation." + +Now Uniformitarianism, as we have seen, tends to ignore geological +speculation in this sense altogether. + +The one point the catastrophists and the uniformitarians agreed upon, +when this Society was founded, was to ignore it. And you will find, if +you look back into our records, that our revered fathers in geology +plumed themselves a good deal upon the practical sense and wisdom of this +proceeding. As a temporary measure, I do not presume to challenge its +wisdom; but in all organised bodies temporary changes are apt to produce +permanent effects; and as time has slipped by, altering all the +conditions which may have made such mortification of the scientific flesh +desirable, I think the effect of the stream of cold water which has +steadily flowed over geological speculation within these walls has been +of doubtful beneficence. + +The sort of geological speculation to which I am now referring +(geological aetiology, in short) was created, as a science, by that famous +philosopher Immanuel Kant, when, in 1775, he wrote his "General Natural +History and Theory of the Celestial Bodies; or an Attempt to account for +the Constitutional and the Mechanical Origin of the Universe upon +Newtonian principles."[11] + +[Footnote 11: Grant (_History of Physical Astronomy_, p. 574) makes but +the briefest reference to Kant.] + +In this very remarkable but seemingly little-known treatise,[12] Kant +expounds a complete cosmogony, in the shape of a theory of the causes +which have led to the development of the universe from diffused atoms of +matter endowed with simple attractive and repulsive forces. + +[Footnote 12: "Allgemeine Naturgeschichte und Theorie des Himmels; oder +Versuch von der Verfassung und dem mechanischen Ursprunge des ganzen +Weltgebäudes nach Newton'schen Grundsatzen abgehandelt."--KANT'S +_Sämmtliche Werke_, Bd. i. p. 207.] + +"Give me matter," says Kant, "and I will build the world;" and he +proceeds to deduce from the simple data from which he starts, a doctrine +in all essential respects similar to the well-known "Nebular Hypothesis" +of Laplace.[13] He accounts for the relation of the masses and the +densities of the planets to their distances from the sun, for the +eccentricities of their orbits, for their rotations, for their +satellites, for the general agreement in the direction of rotation among +the celestial bodies, for Saturn's ring, and for the zodiacal light. He +finds in each system of worlds, indications that the attractive force of +the central mass will eventually destroy its organisation, by +concentrating upon itself the matter of the whole system; but, as the +result of this concentration, he argues for the development of an amount +of heat which will dissipate the mass once more into a molecular chaos +such as that in which it began. + +[Footnote 13: _Système du Monde_, tome ii. chap. 6.] + +Kant pictures to himself the universe as once an infinite expansion of +formless and diffused matter. At one point of this he supposes a single +centre of attraction set up; and, by strict deductions from admitted +dynamical principles, shows how this must result in the development of a +prodigious central body, surrounded by systems of solar and planetary +worlds in all stages of development. In vivid language he depicts the +great world-maelstrom, widening the margins of its prodigious eddy in the +slow progress of millions of ages, gradually reclaiming more and more of +the molecular waste, and converting chaos into cosmos. But what is gained +at the margin is lost in the centre; the attractions of the central +systems bring their constituents together, which then, by the heat +evolved, are converted once more into molecular chaos. Thus the worlds +that are, lie between the ruins of the worlds that have been, and the +chaotic materials of the worlds that shall be; and in spite of all waste +and destruction, Cosmos is extending his borders at the expense of Chaos. + +Kant's further application of his views to the earth itself is to be +found in his "Treatise on Physical Geography"[14] (a term under which the +then unknown science of geology was included), a subject which he had +studied with very great care and on which he lectured for many years. The +fourth section of the first part of this Treatise is called "History of +the great Changes which the Earth has formerly undergone and is still +undergoing," and is, in fact, a brief and pregnant essay upon the +principles of geology. Kant gives an account first "of the gradual +changes which are now taking place" under the heads of such as are caused +by earthquakes, such as are brought about by rain and rivers, such as are +effected by the sea, such as are produced by winds and frost; and, +finally, such as result from the operations of man. + +[Footnote 14: Kant's _Sämmtliche Werke_, Bd. viii. p. 145.] + +The second part is devoted to the "Memorials of the Changes which the +Earth has undergone in remote Antiquity." These are enumerated as:--A. +Proofs that the sea formerly covered the whole earth. B. Proofs that the +sea has often been changed into dry land and then again into sea. C. A +discussion of the various theories of the earth put forward by +Scheuchzer, Moro, Bonnet, Woodward, White, Leibnitz, Linnaeus, and Buffon. + +The third part contains an "Attempt to give a sound explanation of the +ancient history of the earth." + +I suppose that it would be very easy to pick holes in the details of +Kant's speculations, whether cosmological, or specially telluric, in +their application. But for all that, he seems to me to have been the +first person to frame a complete system of geological speculation by +founding the doctrine of evolution. + +With as much truth as Hutton, Kant could say, "I take things just as I +find them at present, and, from these, I reason with regard to that which +must have been." Like Hutton, he is never tired of pointing out that "in +Nature there is wisdom, system, and consistency." And, as in these great +principles, so in believing that the cosmos has a reproductive operation +"by which a ruined constitution may be repaired," he forestalls Hutton; +while, on the other hand, Kant is true to science. He knows no bounds to +geological speculation but those of the intellect. He reasons back to a +beginning of the present state of things; he admits the possibility of an +end. + +I have said that the three schools of geological speculation which I have +termed Catastrophism, Uniformitarianism, and Evolutionism, are commonly +supposed to be antagonistic to one another; and I presume it will have +become obvious that in my belief, the last is destined to swallow up the +other two. But it is proper to remark that each of the latter has kept +alive the tradition of precious truths. + +CATASTROPHISM has insisted upon the existence of a practically unlimited +bank of force, on which the theorist might draw; and it has cherished the +idea of the development of the earth from a state in which its form, and +the forces which it exerted, were very different from those we now know. +That such difference of form and power once existed is a necessary part +of the doctrine of evolution. + +UNIFORMITARIANISM, on the other hand, has with equal justice insisted +upon a practically unlimited bank of time, ready to discount any quantity +of hypothetical paper. It has kept before our eyes the power of the +infinitely little, time being granted, and has compelled us to exhaust +known causes, before flying to the unknown. + +To my mind there appears to be no sort of necessary theoretical +antagonism between Catastrophism and Uniformitarianism. On the contrary, +it is very conceivable that catastrophes may be part and parcel of +uniformity. Let me illustrate my case by analogy. The working of a clock +is a model of uniform action; good time-keeping means uniformity of +action. But the striking of the clock is essentially a catastrophe; the +hammer might be made to blow up a barrel of gunpowder, or turn on a +deluge of water; and, by proper arrangement, the clock, instead of +marking the hours, might strike at all sorts of irregular periods, never +twice alike, in the intervals, force, or number of its blows. +Nevertheless, all these irregular, and apparently lawless, catastrophes +would be the result of an absolutely uniformitarian action; and we might +have two schools of clock-theorists, one studying the hammer and the +other the pendulum. + +Still less is there any necessary antagonists between either of these +doctrines and that of Evolution, which embraces all that is sound in both +Catastrophism and Uniformitarianism, while it rejects the arbitrary +assumptions of the one and the, as arbitrary, limitations of the other. +Nor is the value of the doctrine of Evolution to the philosophic thinker +diminished by the fact that it applies the same method to the living and +the not-living world; and embraces, in one stupendous analogy, the growth +of a solar system from molecular chaos, the shaping of the earth from the +nebulous cub-hood of its youth, through innumerable changes and +immeasurable ages, to its present form; and the development of a living +being from the shapeless mass of protoplasm we term a germ. + +I do not know whether Evolutionism can claim that amount of currency +which would entitle it to be called British popular geology; but, more or +less vaguely, it is assuredly present in the minds of most geologists. + +Such being the three phases of geological speculation, we are now in +position to inquire which of these it is that Sir William Thomson calls +upon us to reform in the passages which I have cited. + +It is obviously Uniformitarianism which the distinguished physicist takes +to be the representative of geological speculation in general. And thus a +first issue is raised, inasmuch as many persons (and those not the least +thoughtful among the younger geologists) do not accept strict +Uniformitarianism as the final form of geological speculation. We should +say, if Hutton and Playfair declare the course of the world to have been +always the same, point out the fallacy by all means; but, in so doing, do +not imagine that you are proving modern geology to be in opposition to +natural philosophy. I do not suppose that, at the present day, any +geologist would be found to maintain absolute Uniformitarianism, to deny +that the rapidity of the rotation of the earth _may_ be diminishing, that +the sun _may_ be waxing dim, or that the earth itself _may_ be cooling. +Most of us, I suspect, are Gallios, "who care for none of these things," +being of opinion that, true or fictitious, they have made no practical +difference to the earth, during the period of which a record is preserved +in stratified deposits. + +The accusation that we have been running counter to the _principles_ of +natural philosophy, therefore, is devoid of foundation. The only question +which can arise is whether we have, or have not, been tacitly making +assumptions which are in opposition to certain conclusions which may be +drawn from those principles. And this question subdivides itself into +two:--the first, are we really contravening such conclusions? the second, +if we are, are those conclusions so firmly based that we may not +contravene them? I reply in the negative to both these questions, and I +will give you my reasons for so doing. Sir William Thomson believes that +he is able to prove, by physical reasonings, "that the existing state of +things on the earth, life on the earth--all geological history showing +continuity of life--must be limited within some such period of time as +one hundred million years" (_loc. cit._ p. 25). + +The first inquiry which arises plainly is, has it ever been denied that +this period _may_ be enough for the purposes of geology? + +The discussion of this question is greatly embarrassed by the vagueness +with which the assumed limit is, I will not say defined, but indicated,-- +"some such period of past time as one hundred million years." Now does +this mean that it may have been two, or three, or four hundred million +years? Because this really makes all the difference.[15] + +[Footnote 15: Sir William Thomson implies (_loc. cit_. p. 16) that the +precise time is of no consequence: "the principle is the same"; but, as +the principle is admitted, the whole discussion turns on its practical +results.] + +I presume that 100,000 feet may be taken as a full allowance for the +total thickness of stratified rocks containing traces of life; 100,000 +divided by 100,000,000 = 0.001. Consequently, the deposit of 100,000 feet +of stratified rock in 100,000,000 years means that the deposit has taken +place at the rate of 1/1000 of a foot, or, say, 1/83 of an inch, per +annum. + +Well, I do not know that any one is prepared to maintain that, even +making all needful allowances, the stratified rocks may not have been +formed, on the average, at the rate of 1/83 of an inch per annum. I +suppose that if such could be shown to be the limit of world-growth, we +could put up with the allowance without feeling that our speculations had +undergone any revolution. And perhaps, after all, the qualifying phrase +"some such period" may not necessitate the assumption of more than 1/166 +or 1/249 or 1/332 of an inch of deposit per year, which, of course, would +give us still more ease and comfort. + +But, it may be said, that it is biology, and not geology, which asks for +so much time--that the succession of life demands vast intervals; but +this appears to me to be reasoning in a circle. Biology takes her time +from geology. The only reason we have for believing in the slow rate of +the change in living forms is the fact that they persist through a series +of deposits which, geology informs us, have taken a long while to make. +If the geological clock is wrong, all the naturalist will have to do is +to modify his notions of the rapidity of change accordingly. And I +venture to point out that, when we are told that the limitation of the +period during which living beings have inhabited this planet to one, two, +or three hundred million years requires a complete revolution in +geological speculation, the _onus probandi_ rests on the maker of the +assertion, who brings forward not a shadow of evidence in its support. + +Thus, if we accept the limitation of time placed before us by Sir W. +Thomson, it is not obvious, on the face of the matter, that we shall have +to alter, or reform, our ways in any appreciable degree; and we may +therefore proceed with much calmness, and indeed much indifference, as to +the result, to inquire whether that limitation is justified by the +arguments employed in its support. + +These arguments are three in number.-- + +I. The first is based upon the undoubted fact that the tides tend to +retard the rate of the earth's rotation upon its axis. That this must be +so is obvious, if one considers, roughly, that the tides result from the +pull which the sun and the moon exert upon the sea, causing it to act as +a sort of break upon the rotating solid earth. + +Kant, who was by no means a mere "abstract philosopher," but a good +mathematician and well versed in the physical science of his time, not +only proved this in an essay of exquisite clearness and intelligibility, +now more than a century old,[16] but deduced from it some of its more +important consequences, such as the constant turning of one face of the +moon towards the earth. + +[Footnote 16: "Untersuchung der Frage oh die Erde in ihrer Umdrehung um +die Achse, wodurch sie die Abwechselung des Tages und der Nacht +hervorbringt, einige Veränderung seit den ersten Zeiten ihres Ursprunges +erlitten habe, &c."--KANT's _Sämmntliche Werke_, Bd. i. p. 178.] + +But there is a long step from the demonstration of a tendency to the +estimation of the practical value of that tendency, which is all with +which we are at present concerned. The facts bearing on this point appear +to stand as follows:-- + +It is a matter of observation that the moon's mean motion is (and has for +the last 3,000 years been) undergoing an acceleration, relatively to the +rotation of the earth. Of course this may result from one of two causes: +the moon may really have been moving more swiftly in its orbit; or the +earth may have been rotating more slowly on its axis. + +Laplace believed he had accounted for this phenomenon by the fact that +the eccentricity of the earth's orbit has been diminishing throughout +these 3,000 years. This would produce a diminution of the mean attraction +of the sun on the moon; or, in other words, an increase in the attraction +of the earth on the moon; and, consequently, an increase in the rapidity +of the orbital motion of the latter body. Laplace, therefore, laid the +responsibility of the acceleration upon the moon, and if his views were +correct, the tidal retardation must either be insignificant in amount, or +be counteracted by some other agency. + +Our great astronomer, Adams, however, appears to have found a flaw in +Laplace's calculation, and to have shown that only half the observed +retardation could be accounted for in the way he had suggested. There +remains, therefore, the other half to be accounted for; and here, in the +absence of all positive knowledge, three sets of hypotheses have been +suggested. + +(_a_.) M. Delaunay suggests that the earth is at fault, in consequence of +the tidal retardation. Messrs. Adams, Thomson, and Tait work out this +suggestion, and, "on a certain assumption as to the proportion of +retardations due to the sun and moon," find the earth may lose twenty-two +seconds of time in a century from this cause.[17] + +[Footnote 17: Sir W. Thomson, _loc. cit_. p. 14.] + +(_b_.) But M. Dufour suggests that the retardation of the earth (which is +hypothetically assumed to exist) may be due in part, or wholly, to the +increase of the moment of inertia of the earth by meteors falling upon +its surface. This suggestion also meets with the entire approval of Sir +W. Thomson, who shows that meteor-dust, accumulating at the rate of one +foot in 4,000 years, would account for the remainder of retardation.[18] + +[Footnote 18: _Ibid._ p. 27.] + +(_c_.) Thirdly, Sir W. Thomson brings forward an hypothesis of his own +with respect to the cause of the hypothetical retardation of the earth's +rotation:-- + +"Let us suppose ice to melt from the polar regions (20° round each pole, +we may say) to the extent of something more than a foot thick, enough to +give 1.1 foot of water over those areas, or 0.006 of a foot of water if +spread over the whole globe, which would, in reality, raise the sea-level +by only some such undiscoverable difference as three-fourths of an inch +or an inch. This, or the reverse, which we believe might happen any year, +and could certainly not be detected without far more accurate +observations and calculations for the mean sea-level than any hitherto +made, would slacken or quicken the earth's rate as a timekeeper by one- +tenth of a second per year."[19] + +[Footnote 19: _Ibid._] + +I do not presume to throw the slightest doubt upon the accuracy of any of +the calculations made by such distinguished mathematicians as those who +have made the suggestions I have cited. On the contrary, it is necessary +to my argument to assume that they are all correct. But I desire to point +out that this seems to be one of the many cases in which the admitted +accuracy of mathematical process is allowed to throw a wholly +inadmissible appearance of authority over the results obtained by them. +Mathematics may be compared to a mill of exquisite workmanship, which +grinds you stuff of any degree of fineness; but, nevertheless, what you +get out depends upon what you put in; and as the grandest mill in the +world will not extract wheat-flour from peascods, so pages of formulae +will not get a definite result out of loose data. + +In the present instance it appears to be admitted:-- + +1. That it is not absolutely certain, after all, whether the moon's mean +motion is undergoing acceleration, or the earth's rotation +retardation.[20] And yet this is the key of the whole position. + +[Footnote 20: It will be understood that I do not wish to deny that the +earth's rotation _may be_ undergoing retardation.] + +2. If the rapidity of the earth's rotation is diminishing, it is not +certain how much of that retardation is due to tidal friction, how much +to meteors, how much to possible excess of melting over accumulation of +polar ice, during the period covered by observation, which amounts, at +the outside, to not more than 2,600 years. + +3. The effect of a different distribution of land and water in modifying +the retardation caused by tidal friction, and of reducing it, under some +circumstances, to a minimum, does not appear to be taken into account. + +4. During the Miocene epoch the polar ice was certainly many feet thinner +than it has been during, or since, the Glacial epoch. Sir W. Thomson +tells us that the accumulation of something more than a foot of ice +around the poles (which implies the withdrawal of, say, an inch of water +from the general surface of the sea) will cause the earth to rotate +quicker by one-tenth of a second per annum. It would appear, therefore, +that the earth may have been rotating, throughout the whole period which +has elapsed from the commencement of the Glacial epoch down to the +present time, one, or more, seconds per annum quicker than it rotated +during the Miocene epoch. + +But, according to Sir W. Thomson's calculation, tidal retardation will +only account for a retardation of 22" in a century, or 22/100 (say 1/5) +of a second per annum. + +Thus, assuming that the accumulation of polar ice since the Miocene epoch +has only been sufficient to produce ten times the effect of a coat of ice +one foot thick, we shall have an accelerating cause which covers all the +loss from tidal action, and leaves a balance of 4/5 of a second per annum +in the way of acceleration. + +If tidal retardation can be thus checked and overthrown by other +temporary conditions, what becomes of the confident assertion, based upon +the assumed uniformity of tidal retardation, that ten thousand million +years ago the earth must have been rotating more than twice as fast as at +present, and, therefore, that we geologists are "in direct opposition to +the principles of Natural Philosophy" if we spread geological history +over that time? + +II. The second argument is thus stated by Sir W. Thomson:--"An article, +by myself, published in 'Macmillan's Magazine' for March 1862, on the age +of the sun's heat, explains results of investigation into various +questions as to possibilities regarding the amount of heat that the sun +could have, dealing with it as you would with a stone, or a piece of +matter, only taking into account the sun's dimensions, which showed it to +be possible that the sun may have already illuminated the earth for as +many as one hundred million years, but at the same time rendered it +almost certain that he had not illuminated the earth for five hundred +millions of years. The estimates here are necessarily very vague; but +yet, vague as they are, I do not know that it is possible, upon any +reasonable estimate founded on known properties of matter, to say that we +can believe the sun has really illuminated the earth for five hundred +million years."[21] + +[Footnote 21: _Loc. cit._ p. 20.] + +I do not wish to "Hansardise" Sir William Thomson by laying much stress +on the fact that, only fifteen years ago he entertained a totally +different view of the origin of the sun's heat, and believed that the +energy radiated from year to year was supplied from year to year--a +doctrine which would have suited Hutton perfectly. But the fact that so +eminent a physical philosopher has, thus recently, held views opposite to +those which he now entertains, and that he confesses his own estimates to +be "very vague," justly entitles us to disregard those estimates, if any +distinct facts on our side go against them. However, I am not aware that +such facts exist. As I have already said, for anything I know, one, two, +or three hundred millions of years may serve the needs of geologists +perfectly well. + +III. The third line of argument is based upon the temperature of the +interior of the earth. Sir W. Thomson refers to certain investigations +which prove that the present thermal condition of the interior of the +earth implies either a heating of the earth within the last 20,000 years +of as much as 100° F., or a greater heating all over the surface at some +time further back than 20,000 years, and then proceeds thus:-- + +"Now, are geologists prepared to admit that, at some time within the last +20,000 years, there has been all over the earth so high a temperature as +that? I presume not; no geologist--no _modern_ geologist--would for a +moment admit the hypothesis that the present state of underground heat is +due to a heating of the surface at so late a period as 20,000 years ago. +If that is not admitted we are driven to a greater heat at some time more +than 20,000 years ago. A greater heating all over the surface than 100° +Fahrenheit would kill nearly all existing plants and animals, I may +safely say. Are modern geologists prepared to say that all life was +killed off the earth 50,000, 100,000, or 200,000 years ago? For the +uniformity theory, the further back the time of high surface-temperature +is put the better; but the further back the time of heating, the hotter +it must have been. The best for those who draw most largely on time is +that which puts it furthest back; and that is the theory that the heating +was enough to melt the whole. But even if it was enough to melt the +whole, we must still admit some limit, such as fifty million years, one +hundred million years, or two or three hundred million years ago. Beyond +that we cannot go."[22] + +[Footnote 22: _Loc. cit._ p. 24.] + +It will be observed that the "limit" is once again of the vaguest, +ranging from 50,000,000 years to 300,000,000. And the reply is, once +more, that, for anything that can be proved to the contrary, one or two +hundred million years might serve the purpose, even of a thoroughgoing +Huttonian uniformitarian, very well. + +But if, on the other hand, the 100,000,000 or 200,000,000 years appear to +be insufficient for geological purposes, we must closely criticise the +method by which the limit is reached. The argument is simple enough. +_Assuming_ the earth to be nothing but a cooling mass, the quantity of +heat lost per year, _supposing_ the rate of cooling to have been uniform, +multiplied by any given number of years, will be given the minimum +temperature that number of years ago. + +But is the earth nothing but a cooling mass, "like a hot-water jar such +as is used in carriages," or "a globe of sandstone," and has its cooling +been uniform? An affirmative answer to both these questions seems to be +necessary to the validity of the calculations on which Sir W. Thomson +lays so much stress. + +Nevertheless it surely may be urged that such affirmative answers are +purely hypothetical, and that other suppositions have an equal right to +consideration. + +For example, is it not possible that, at the prodigious temperature which +would seem to exist at 100 miles below the surface, all the metallic +bases may behave as mercury does at a red heat, when it refuses to +combine with oxygen; while, nearer the surface, and therefore at a lower +temperature, they may enter into combination (as mercury does with oxygen +a few degrees below its boiling-point), and so give rise to a heat +totally distinct from that which they possess as cooling bodies? And has +it not also been proved by recent researches that the quality of the +atmosphere may immensely affect its permeability to heat; and, +consequently, profoundly modify the rate of cooling the globe as a whole? + +I do not think it can be denied that such conditions may exist, and may +so greatly affect the supply, and the loss, of terrestrial heat as to +destroy the value of any calculations which leave them out of sight. + +My functions as your advocate are at an end. I speak with more than the +sincerity of a mere advocate when I express the belief that the case +against us has entirely broken down. The cry for reform which has been +raised without, is superfluous, inasmuch as we have long been reforming +from within, with all needful speed. And the critical examination of the +grounds upon which the very grave charge of opposition to the principles +of Natural Philosophy has been brought against us, rather shows that we +have exercised a wise discrimination in declining, for the present, to +meddle with our foundations. + + + +XI + + +PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION + +[1870] + +It is now eight years since, in the absence of the late Mr. Leonard +Horner, who then presided over us, it fell to my lot, as one of the +Secretaries of this Society, to draw up the customary Annual Address. I +availed myself of the opportunity to endeavour to "take stock" of that +portion of the science of biology which is commonly called +"palaeontology," as it then existed; and, discussing one after another the +doctrines held by palaeontologists, I put before you the results of my +attempts to sift the well-established from the hypothetical or the +doubtful. Permit me briefly to recall to your minds what those results +were:-- + +1. The living population of all parts of the earth's surface which have +yet been examined has undergone a succession of changes which, upon the +whole, have been of a slow and gradual character. + +2. When the fossil remains which are the evidences of these successive +changes, as they have occurred in any two more or less distant parts of +the surface of the earth, are compared, they exhibit a certain broad and +general parallelism. In other words, certain forms of life in one +locality occur in the same general order of succession as, or are +_homotaxial_ with, similar forms in the other locality. + +3. Homotaxis is not to be held identical with synchronism without +independent evidence. It is possible that similar, or even identical, +faunae and florae in two different localities may be of extremely different +ages, if the term "age" is used in its proper chronological sense. I +stated that "geographical provinces, or zones, may have been as +distinctly marked in the Palaeozoic epoch as at present; and those +seemingly sudden appearances of new genera and species which we ascribe +to new creation, may be simple results of migration." + +4. The opinion that the oldest known fossils are the earliest forms of +life has no solid foundation. + +5. If we confine ourselves to positively ascertained facts, the total +amount of change in the forms of animal and vegetable life, since the +existence of such forms is recorded, is small. When compared with the +lapse of time since the first appearance of these forms, the amount of +change is wonderfully small. Moreover, in each great group of the animal +and vegetable kingdoms, there are certain forms which I termed PERSISTENT +TYPES, which have remained, with but very little apparent change, from +their first appearance to the present time. + +6. In answer to the question "What, then, does an impartial survey of the +positively ascertained truths of palaeontology testify in relation to the +common doctrines of progressive modification, which suppose that +modification to have taken place by a necessary progress from more to +less embryonic forms, from more to less generalised types, within the +limits of the period represented by the fossiliferous rocks?" I reply, +"It negatives these doctrines; for it either shows us no evidence of such +modification, or demonstrates such modification as has occurred to have +been very slight; and, as to the nature of that modification, it yields +no evidence whatsoever that the earlier members of any long-continued +group were more generalised in structure than the later ones." + +I think that I cannot employ my last opportunity of addressing you, +officially, more properly--I may say more dutifully--than in revising +these old judgments with such help as further knowledge and reflection, +and an extreme desire to get at the truth, may afford me. + +1. With respect to the first proposition, I may remark that whatever may +be the case among the physical geologists, catastrophic palaeontologists +are practically extinct. It is now no part of recognised geological +doctrine that the species of one formation all died out and were replaced +by a brand-new set in the next formation. On the contrary, it is +generally, if not universally, agreed that the succession of life has +been the result of a slow and gradual replacement of species by species; +and that all appearances of abruptness of change are due to breaks in the +series of deposits, or other changes in physical conditions. The +continuity of living forms has been unbroken from the earliest times to +the present day. + +2, 3. The use of the word "homotaxis" instead of "synchronism" has not, +so far as I know, found much favour in the eyes of geologists. I hope, +therefore, that it is a love for scientific caution, and not mere +personal affection for a bantling of my own, which leads me still to +think that the change of phrase is of importance, and that the sooner it +is made, the sooner shall we get rid of a number of pitfalls which beset +the reasoner upon the facts and theories of geology. + +One of the latest pieces of foreign intelligence which has reached us is +the information that the Austrian geologists have, at last, succumbed to +the weighty evidence which M. Barrande has accumulated, and have admitted +the doctrine of colonies. But the admission of the doctrine of colonies +implies the further admission that even identity of organic remains is no +proof of the synchronism of the deposits which contain them. + +4. The discussions touching the _Eozoon,_ which commenced in 1864, have +abundantly justified the fourth proposition. In 1862, the oldest record +of life was in the Cambrian rocks; but if the _Eozoon_ be, as Principal +Dawson and Dr. Carpenter have shown so much reason for believing, the +remains of a living being, the discovery of its true nature carried life +back to a period which, as Sir William Logan has observed, is as remote +from that during which the Cambrian rocks were deposited, as the Cambrian +epoch itself is from the tertiaries. In other words, the ascertained +duration of life upon the globe was nearly doubled at a stroke. + +5. The significance of persistent types, and of the small amount of +change which has taken place even in those forms which can be shown to +have been modified, becomes greater and greater in my eyes, the longer I +occupy myself with the biology of the past. + +Consider how long a time has elapsed since the Miocene epoch. Yet, at +that time there is reason to believe that every important group in every +order of the _Mammalia_ was represented. Even the comparatively scanty +Eocene fauna yields examples of the orders _Cheiroptera, Insectivora, +Rodentia_, and _Perissodactyla_; of _Artiodactyla_ under both the +Ruminant and the Porcine modifications; of _Caranivora, Cetacea_, and +_Marsupialia_. + +Or, if we go back to the older half of the Mesozoic epoch, how truly +surprising it is to find every order of the _Reptilia_, except the +_Ophidia_, represented; while some groups, such as the _Ornithoseclida_ +and the _Pterosauria_, more specialised than any which now exist, +abounded. + +There is one division of the _Amphibia_ which offers especially important +evidence upon this point, inasmuch as it bridges over the gap between the +Mesozoic and the Palaeozoic formations (often supposed to be of such +prodigious magnitude), extending, as it does, from the bottom of the +Carboniferous series to the top of the Trias, if not into the Lias. I +refer to the Labyrinthodonts. As the Address of 1862 was passing through +the press, I was able to mention, in a note, the discovery of a large +Labyrinthodont, with well-ossified vertebrae, in the Edinburgh coal-field. +Since that time eight or ten distinct genera of Labyrinthodonts have been +discovered in the Carboniferous rocks of England, Scotland, and Ireland, +not to mention the American forms described by Principal Dawson and +Professor Cope. So that, at the present time, the Labyrinthodont Fauna of +the Carboniferous rocks is more extensive and diversified than that of +the Trias, while its chief types, so far as osteology enables us to +judge, are quite as highly organised. Thus it is certain that a +comparatively highly organised vertebrate type, such as that of the +Labyrinthodonts, is capable of persisting, with no considerable change, +through the period represented by the vast deposits which constitute the +Carboniferous, the Permian, and the Triassic formations. + +The very remarkable results which have been brought to light by the +sounding and dredging operations, which have been carried on with such +remarkable success by the expeditions sent out by our own, the American, +and the Swedish Governments, under the supervision of able naturalists, +have a bearing in the same direction. These investigations have +demonstrated the existence, at great depths in the ocean, of living +animals in some cases identical with, in others very similar to, those +which are found fossilised in the white chalk. The _Globigerinoe_, +Cyatholiths, Coccospheres, Discoliths in the one are absolutely identical +with those in the other; there are identical, or closely analogous, +species of Sponges, Echinoderms, and Brachiopods. Off the coast of +Portugal, there now lives a species of _Beryx_, which, doubtless, leaves +its bones and scales here and there in the Atlantic ooze, as its +predecessor left its spoils in the mud of the sea of the Cretaceous +epoch. + +Many years ago[1] I ventured to speak of the Atlantic mud as "modern +chalk," and I know of no fact inconsistent with the view which Professor +Wyville Thomson has advocated, that the modern chalk is not only the +lineal descendant of the ancient chalk, but that it remains, so to speak, +in the possession of the ancestral estate; and that from the Cretaceous +period (if not much earlier) to the present day, the deep sea has covered +a large part of what is now the area of the Atlantic. But if +_Globigerina_, and _Terebratula caput-serpentis_ and _Beryx_, not to +mention other forms of animals and of plants, thus bridge over the +interval between the present and the Mesozoic periods, is it possible +that the majority of other living things underwent a "sea-change into +something new and strange" all at once? + +[Footnote 1: See an article in the _Saturday Review_, for 1858, on +"Chalk, Ancient and Modern."] + +6. Thus far I have endeavoured to expand and to enforce by fresh +arguments, but not to modify in any important respect, the ideas +submitted to you on a former occasion. But when I come to the +propositions touching progressive modification, it appears to me, with +the help of the new light which has broken from various quarters, that +there is much ground for softening the somewhat Brutus-like severity with +which, in 1862, I dealt with a doctrine, for the truth of which I should +have been glad enough to be able to find a good foundation. So far, +indeed, as the _Invertebrata_ and the lower _Vertebrata_ are concerned, +the facts and the conclusions which are to be drawn from them appear to +me to remain what they were. For anything that, as yet, appears to the +contrary, the earliest known Marsupials may have been as highly organised +as their living congeners; the Permian lizards show no signs of +inferiority to those of the present day; the Labyrinthodonts cannot be +placed below the living Salamander and Triton; the Devonian Ganoids are +closely related to _Polypterus_ and to _Lepidosiren_. + +But when we turn to the higher _Vertebrata_, the results of recent +investigations, however we may sift and criticise them, seem to me to +leave a clear balance in favour of the doctrine of the evolution of +living forms one from another. Nevertheless, in discussing this question, +it is very necessary to discriminate carefully between the different +kinds of evidence from fossil remains which are brought forward in favour +of evolution. + +Every fossil which takes an intermediate place between forms of life +already known, may be said, so far as it is intermediate, to be evidence +in favour of evolution, inasmuch as it shows a possible road by which +evolution may have taken place. But the mere discovery of such a form +does not, in itself, prove that evolution took place by and through it, +nor does it constitute more than presumptive evidence in favour of +evolution in general. Suppose A, B, C to be three forms, while B is +intermediate in structure between A and C. Then the doctrine of evolution +offers four possible alternatives. A may have become C by way of B; or C +may have become A by way of B; or A and C may be independent +modifications of B; or A, B, and C may be independent modifications of +some unknown D. Take the case of the Pigs, the _Anoplothcridoe_, and the +Ruminants. The _Anoplothcridoe_ are intermediate between the first and +the last; but this does not tell us whether the Ruminants have come from +the Pigs, or the Pigs from Ruminants, or both from _Anoplothcridoe_, or +whether Pigs, Ruminants, and _Anoplotlicridoe_ alike may not have +diverged from some common stock. + +But if it can be shown that A, B, and C exhibit successive stages in the +degree of modification, or specialisation, of the same type; and if, +further, it can be proved that they occur in successively newer deposits, +A being in the oldest and C in the newest, then the intermediate +character of B has quite another importance, and I should accept it, +without hesitation, as a link in the genealogy of C. I should consider +the burden of proof to be thrown upon any one who denied C to have been +derived from A by way of B, or in some closely analogous fashion; for it +is always probable that one may not hit upon the exact line of filiation, +and, in dealing with fossils, may mistake uncles and nephews for fathers +and sons. + +I think it necessary to distinguish between the former and the latter +classes of intermediate forms, as _intercalary types_ and _linear types_. +When I apply the former term, I merely mean to say that as a matter of +fact, the form B, so named, is intermediate between the others, in the +sense in which the _Anoplotherium_ is intermediate between the Pigs and +the Ruminants--without either affirming, or denying, any direct genetic +relation between the three forms involved. When I apply the latter term, +on the other hand, I mean to express the opinion that the forms A, B, and +C constitute a line of descent, and that B is thus part of the lineage of +C. + +From the time when Cuvier's wonderful researches upon the extinct Mammals +of the Paris gypsum first made intercalary types known, and caused them +to be recognised as such, the number of such forms has steadily increased +among the higher _Mammalia_. Not only do we now know numerous intercalary +forins of _Ungulata_, but M. Gaudry's great monograph upon the fossils of +Pikermi (which strikes me as one of the most perfect pieces of +palaeontological work I have seen for a long time) shows us, among the +Primates, _Mesopithecus_ as an intercalary form between the +_Semnopitheci_ and the _Macaci_; and among the _Carnivora_, _Hyoenictis_ +and _Ictitherium_ as intercalary, or, perhaps, linear types between the +_Viverridoe_ and the _Hyoenidoe_. + +Hardly any order of the higher _Mammalia_ stands so apparently separate +and isolated from the rest as that of the _Cetacea_; though a careful +consideration of the structure of the pinnipede _Carnivora_, or Seals, +shows, in them, many an approximation towards the still more completely +marine mammals. The extinct _Zeuglodon_, however, presents us with an +intercalary form between the type of the Seals and that of the Whales. +The skull of this great Eocene sea-monster, in fact, shows by the narrow +and prolonged interorbital region; the extensive union of the parietal +bones in a sagittal suture; the well-developed nasal bones; the distinct +and large incisors implanted in premaxillary bones, which take a full +share in bounding the fore part of the gape; the two-fanged molar teeth +with triangular and serrated crowns, not exceeding five on each side in +each jaw; and the existence of a deciduous dentition--its close relation +with the Seals. While, on the other hand, the produced rostral form of +the snout, the long symphysis, and the low coronary process of the +mandible are approximations to the cetacean form of those parts. + +The scapula resembles that of the cetacean _Hyperoodon_, but the supra- +spinous fossa is larger and more seal-like; as is the humerus, which +differs from that of the _Cetacea_ in presenting true articular surfaces +for the free jointing of the bones of the fore-arm. In the apparently +complete absence of hinder limbs, and in the characters of the vertebral +column, the _Zeuglodon_ lies on the cetacean side of the boundary line; +so that upon the whole, the Zeuglodonts, transitional as they are, are +conveniently retained in the cetacean order. And the publication, in +1864, of M. Van Beneden's memoir on the Miocene and Pliocene _Squalodon_, +furnished much better means than anatomists previously possessed of +fitting in another link of the chain which connects the existing +_Cetacea_ with _Zeuglodon_. The teeth are much more numerous, although +the molars exhibit the zeuglodont double fang; the nasal bones are very +short, and the upper surface of the rostrum presents the groove, filled +up during life by the prolongation of the ethmoidal cartilage, which is +so characteristic of the majority of the _Cetacea_. + +It appears to me that, just as among the existing _Carnivora_, the +walruses and the eared seals are intercalary forms between the fissipede +Carnivora and the ordinary seals, so the Zeuglodonts are intercalary +between the _Carnivora_, as a whole, and the _Cetacea_. Whether the +Zeuglodonts are also linear types in their relation to these two groups +cannot be ascertained, until we have more definite knowledge than we +possess at present, respecting the relations in time of the _Carnivora_ +and _Cetacea_. + +Thus far we have been concerned with the intercalary types which occupy +the intervals between Families or Orders of the same class; but the +investigations which have been carried on by Professor Gegenbaur, +Professor Cope, and myself into the structure and relations of the +extinct reptilian forms of the _Ornithoscelida_ (or _Dinosauria_ and +_Compsognatha_) have brought to light the existence of intercalary forms +between what have hitherto been always regarded as very distinct classes +of the vertebrate sub-kingdom, namely _Reptilia_ and _Aves_. Whatever +inferences may, or may not, be drawn from the fact, it is now an +established truth that, in many of these _Ornithoscelida_, the hind limbs +and the pelvis are much more similar to those of Birds than they are to +those of Reptiles, and that these Bird-reptiles, or Reptile-birds, were +more or less completely bipedal. + +When I addressed you in 1862, I should have been bold indeed had I +suggested that palaeontology would before long show us the possibility of +a direct transition from the type of the lizard to that of the ostrich. +At the present moment, we have, in the _Ornithoscelida_, the intercalary +type, which proves that transition to be something more than a +possibility; but it is very doubtful whether any of the genera of +_Ornithoscelida_ with which we are at present acquainted are the actual +linear types by which the transition from the lizard to the bird was +effected. These, very probably, are still hidden from us in the older +formations. + +Let us now endeavour to find some cases of true linear types, or forms +which are intermediate between others because they stand in a direct +genetic relation to them. It is no easy matter to find clear and +unmistakable evidence of filiation among fossil animals; for, in order +that such evidence should be quite satisfactory, it is necessary that we +should be acquainted with all the most important features of the +organisation of the animals which are supposed to be thus related, and +not merely with the fragments upon which the genera and species of the +palaeontologist are so often based. M. Gaudry has arranged the species of +_Hyoenidoe, Proboscidea, Rhinocerotidoe_, and _Equidoe_ in their order of +filiation from their earliest appearance in the Miocene epoch to the +present time, and Professor Rütimeyer has drawn up similar schemes for +the Oxen and other _Ungulata_--with what, I am disposed to think, is a +fair and probable approximation to the order of nature. But, as no one is +better aware than these two learned, acute, and philosophical biologists, +all such arrangements must be regarded as provisional, except in those +cases in which, by a fortunate accident, large series of remains are +obtainable from a thick and widespread series of deposits. It is easy to +accumulate probabilities--hard to make out some particular case in such a +way that it will stand rigorous criticism. + +After much search, however, I think that such a case is to be made out in +favour of the pedigree of the Horses. + +The genus _Equus_ is represented as far back as the latter part of the +Miocene epoch; but in deposits belonging to the middle of that epoch its +place is taken by two other genera, _Hipparion_ and _Anchitherium_;[2] +and, in the lowest Miocene and upper Eocene, only the last genus occurs. +A species of _Anchitherium_ was referred by Cuvier to the _Paloeotheria_ +under the name of _P. aurelianense_. The grinding-teeth are in fact very +similar in shape and in pattern, and in the absence of any thick layer of +cement, to those of some species of _Paloeotherium_, especially Cuvier's +_Paloeotherium minus_, which has been formed into a separate genus, +_Plagiolophus_, by Pomel. But in the fact that there are only six full- +sized grinders in the lower jaw, the first premolar being very small; +that the anterior grinders are as large as, or rather larger than, the +posterior ones; that the second premolar has an anterior prolongation; +and that the posterior molar of the lower jaw has, as Cuvier pointed out, +a posterior lobe of much smaller size and different form, the dentition +of _Anchitherium_ departs from the type of the _Paloeotherium_, and +approaches that of the Horse. + +[Footnote 2: Hermann von Meyer gave the name of _Anchitherium_ to _A. +Ezquerroe_; and in his paper on the subject he takes great pains to +distinguish the latter as the type of a new genus, from Cuvier's +_Paloeotherium d'Orléans_. But it is precisely the _Paloeotherium +d'Orléans_ which is the type of Christol's genus _Hipparitherium_; and +thus, though _Hipparitherium_ is of later date than _Anchitherium_, it +seemed to me to have a sort of equitable right to recognition when this +Address was written. On the whole, however, it seems most convenient to +adopt _Anchitherium_.] + +Again, the skeleton of _Anchitherium_ is extremely equine. M. Christol +goes so far as to say that the description of the bones of the horse, or +the ass, current in veterinary works, would fit those of _Anchitherium_. +And, in a general way, this may be true enough; but there are some most +important differences, which, indeed, are justly indicated by the same +careful observer. Thus the ulna is complete throughout, and its shaft is +not a mere rudiment, fused into one bone with the radius. There are three +toes, one large in the middle and one small on each side. The femur is +quite like that of a horse, and has the characteristic fossa above the +external condyle. In the British Museum there is a most instructive +specimen of the leg-bones, showing that the fibula was represented by the +external malleolus and by a flat tongue of bone, which extends up from it +on the outer side of the tibia, and is closely ankylosed with the latter +bone.[3] The hind toes are three, like those of the fore leg; and the +middle metatarsal bone is much less compressed from side to side than +that of the horse. + +[Footnote 3: I am indebted to M. Gervais for a specimen which indicates +that the fibula was complete, at any rate, in some cases; and for a very +interesting ramps of a mandible, which shows that, as in the +_Paloeotheria_, the hindermost milk-molar of the lower jaw was devoid of +the posterior lobe which exists in the hindermost true molar.] + +In the _Hipparion_, the teeth nearly resemble those of the Horses, though +the crowns of the grinders are not so long; like those of the Horses, +they are abundantly coated with cement. The shaft of the ulna is reduced +to a mere style, ankylosed throughout nearly its whole length with the +radius, and appearing to be little more than a ridge on the surface of +the latter bone until it is carefully examined. The front toes are still +three, but the outer ones are more slender than in _Anchitherium_, and +their hoofs smaller in proportion to that of the middle toe; they are, in +fact, reduced to mere dew-claws, and do not touch the ground. In the leg, +the distal end of the fibula is so completely united with the tibia that +it appears to be a mere process of the latter bone, as in the Horses. + +In _Equus_, finally, the crowns of the grinding-teeth become longer, and +their patterns are slightly modified; the middle of the shaft of the ulna +usually vanishes, and its proximal and distal ends ankylose with the +radius. The phalanges of the two outer toes in each foot disappear, their +metacarpal and metatarsal bones being left as the "splints." + +The _Hipparion_ has large depressions on the face in front of the orbits, +like those for the "larmiers" of many ruminants; but traces of these are +to be seen in some of the fossil horses from the Sewalik Hills; and, as +Leidy's recent researches show, they are preserved in _Anchitherium_. + +When we consider these facts, and the further circumstance that the +Hipparions, the remains of which have been collected in immense numbers, +were subject, as M. Gaudry and others have pointed out, to a great range +of variation, it appears to me impossible to resist the conclusion that +the types of the _Anchitherium_, of the _Hipparion_, and of the ancient +Horses constitute the lineage of the modern Horses, the _Hipparion_ being +the intermediate stage between the other two, and answering to B in my +former illustration. + +The process by which the _Anchitherium_ has been converted into _Equus_ +is one of specialisation, or of more and more complete deviation from +what might be called the average form of an ungulate mammal. In the +Horses, the reduction of some parts of the limbs, together with the +special modification of those which are left, is carried to a greater +extent than in any other hoofed mammals. The reduction is less and the +specialisation is less in the _Hipparion_, and still less in the +_Anchitherium_; but yet, as compared with other mammals, the reduction +and specialisation of parts in the _Anchitherium_ remain great. + +Is it not probable then, that, just as in the Miocene epoch, we find an +ancestral equine form less modified than _Equus_, so, if we go back to +the Eocene epoch, we shall find some quadruped related to the +_Anchitherium_, as _Hipparion_ is related to _Equus_, and consequently +departing less from the average form? + +I think that this desideratum is very nearly, if not quite, supplied by +_Plagiolophus_, remains of which occur abundantly in some parts of the +Upper and Middle Eocene formations. The patterns of the grinding-teeth of +_Plagiolophus_ are similar to those of _Anchitherium_, and their crowns +are as thinly covered with cement; but the grinders diminish in size +forwards, and the last lower molar has a large hind lobe, convex outwards +and concave inwards, as in _Palueotherium_. The ulna is complete and much +larger than in any of the _Equidoe_, while it is more slender than in +most of the true _Paloeotheria_; it is fixedly united, but not ankylosed, +with the radius. There are three toes in the fore limb, the outer ones +being slender, but less attenuated than in the _Equidoe_. The femur is +more like that of the _Paloeotheria_ than that of the horse, and has only +a small depression above its outer condyle in the place of the great +fossa which is so obvious in the _Equidoe_. The fibula is distinct, but +very slender, and its distal end is ankylosed with the tibia. There are +three toes on the hind foot having similar proportions to those on the +fore foot. The principal metacarpal and metatarsal bones are flatter than +they are in any of the _Equidoe_; and the metacarpal bones are longer +than the metatarsals, as in the _Paloeotheria_. + +In its general form, _Plagiolophus_ resembles a very small and slender +horse,[4] and is totally unlike the reluctant, pig-like creature depicted +in Cuvier's restoration of his _Paloeotherium minus_ in the "Ossemens +Fossiles." + +[Footnote 4: Such, at least, is the conclusion suggested by the +proportions of the skeleton figured by Cuvier and De Blainville; but +perhaps something between a Horse and an Agouti would be nearest the +mark.] + +It would be hazardous to say that _Plagiolophus_ is the exact radical +form of the Equine quadrupeds; but I do not think there can be any +reasonable doubt that the latter animals have resulted from the +modification of some quadruped similar to _Plagiolophus_. + +We have thus arrived at the Middle Eocene formation, and yet have traced +back the Horses only to a three-toed stock; but these three-toed forms, +no less than the Equine quadrupeds themselves, present rudiments of the +two other toes which appertain to what I have termed the "average" +quadruped. If the expectation raised by the splints of the Horses that, +in some ancestor of the Horses, these splints would be found to be +complete digits, has been verified, we are furnished with very strong +reasons for looking for a no less complete verification of the +expectation that the three-toed _Plagiolophus_-like "avus" of the horse +must have had a five-toed "atavus" at some earlier period. + +No such five-toed "atavus," however, has yet made its appearance among +the few middle and older Eocene _Mammalia_ which are known. + +Another series of closely affiliated forms, though the evidence they +afford is perhaps less complete than that of the Equine series, is +presented to us by the _Dichobune_ of the Eocene epoch, the +_Cainotherium_ of the Miocene, and the _Tragulidoe_, or so-called "Musk- +deer," of the present day. + +The _Tragulidoe_; have no incisors in the upper jaw, and only six +grinding-teeth on each side of each jaw; while the canine is moved up to +the outer incisor, and there is a diastema in the lower jaw. There are +four complete toes on the hind foot, but the middle metatarsals usually +become, sooner or later, ankylosed into a cannon bone. The navicular and +the cuboid unite, and the distal end of the fibula is ankylosed with the +tibia. + +In _Cainotherium_ and _Dichobune_ the upper incisors are fully developed. +There are seven grinders; the teeth form a continuous series without a +diastema. The metatarsals, the navicular and cuboid, and the distal end +of the fibula, remain free. In the _Cainotherium_, also, the second +metacarpal is developed, but is much shorter than the third, while the +fifth is absent or rudimentary. In this respect it resembles +_Anoplotherium secundarium_. This circumstance, and the peculiar pattern +of the upper molars in _Cainotherium_, lead me to hesitate in considering +it as the actual ancestor of the modern _Tragulidoe_. If _Dichobune_ has +a fore-toed fore foot (though I am inclined to suspect that it resembles +_Cainotherium_), it will be a better representative of the oldest forms +of the Traguline series; but _Dichobune_ occurs in the Middle Eocene, and +is, in fact, the oldest known artiodactyle mammal. Where, then, must we +look for its five-toed ancestor? + +If we follow down other lines of recent and tertiary _Ungulata_, the same +question presents itself. The Pigs are traceable back through the Miocene +epoch to the Upper Eocene, where they appear in the two well-marked forms +of _Hyopopotamus_ and _Choeropotamus_; but _Hyopotamus_ appears to have +had only two toes. + +Again, all the great groups of the Ruminants, the _Bovidoe, Antilopidoe, +Camelopardalidoe_, and _Cervidoe_, are represented in the Miocene epoch, +and so are the Camels. The Upper Eocene _Anoplotherium_, which is +intercalary between the Pigs and the _Tragulidoe_, has only two, or, at +most, three toes. Among the scanty mammals of the Lower Eocene formation +we have the perissodactyle _Ungulata_ represented by _Coryphodon, +Hyracotherium_, and _Pliolophus_. Suppose for a moment, for the sake of +following out the argument, that _Pliolophus_ represents the primary +stock of the Perissodactyles, and _Dichobune_ that of the Artiodactyles +(though I am far from saying that such is the case), then we find, in the +earliest fauna of the Eocene epoch to which our investigations carry us, +the two divisions of the _Ungulata_ completely differentiated, and no +trace of any common stock of both, or of five-toed predecessors to +either. With the case of the Horses before us, justifying a belief in the +production of new animal forms by modification of old ones, I see no +escape from the necessity of seeking for these ancestors of the +_Ungulata_ beyond the limits of the Tertiary formations. + +I could as soon admit special creation, at once, as suppose that the +Perissodactyles and Artiodactyles had no five-toed ancestors. And when we +consider how large a portion of the Tertiary period elapsed before +_Anchitherium_ was converted into _Equus_, it is difficult to escape the +conclusion that a large proportion of time anterior to the Tertiary +period must have been expended in converting the common stock of the +_Ungulata_ into Perissodactyles and Artiodactyles. + +The same moral is inculcated by the study of every other order of +Tertiary monodelphous _Mammalia_. Each of these orders is represented in +the Miocene epoch: the Eocene formation, as I have already said, contains +_Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora_, and _Cetacea_. +But the _Cheiroptera_ are extreme modifications of the _Insectivora_, +just as the _Cetacea_ are extreme modifications of the Carnivorous type; +and therefore it is to my mind incredible that monodelphous _Insectivora_ +and _Carnivora_ should not have been abundantly developed, along with +_Ungulata_, in the Mesozoic epoch. But if this be the case, how much +further back must we go to find the common stock of the monodelphous +_Mammalia_? As to the _Didelphia_, if we may trust the evidence which +seems to be afforded by their very scanty remains, a Hypsiprymnoid form +existed at the epoch of the Trias, contemporaneously with a Carnivorous +form. At the epoch of the Trias, therefore, the _Marsupialia_ must have +already existed long enough to have become differentiated into +carnivorous and herbivorous forms. But the _Monotremata_ are lower forms +than the _Didelphia_ which last are intercalary between the +_Ornithodelphia_ and the _Monodelphia_. To what point of the Palaeozoic +epoch, then, must we, upon any rational estimate, relegate the origin of +the _Monotremata?_ + +The investigation of the occurrence of the classes and of the orders of +the _Sauropsida_ in time points in exactly the same direction. If, as +there is great reason to believe, true Birds existed in the Triassic +epoch, the ornithoscelidous forms by which Reptiles passed into Birds +must have preceded them. In fact there is, even at present, considerable +ground for suspecting the existence of _Dinosauria_ in the Permian +formations; but, in that case, lizards must be of still earlier date. And +if the very small differences which are observable between the +_Crocodilia_ of the older Mesozoic formations and those of the present +day furnish any sort of approximation towards an estimate of the average +rate of change among the _Sauropsida_, it is almost appalling to reflect +how far back in Palaeozoic times we must go, before we can hope to arrive +at that common stock from which the _Crocodilia, Lacertilia, +Ornithoscelida_, and _Plesiosauria_, which had attained so great a +development in the Triassic epoch, must have been derived. + +The _Amphibia_ and _Pisces_ tell the same story. There is not a single +class of vertebrated animals which, when it first appears, is represented +by analogues of the lowest known members of the same class. Therefore, if +there is any truth in the doctrine of evolution, every class must be +vastly older than the first record of its appearance upon the surface of +the globe. But if considerations of this kind compel us to place the +origin of vertebrated animals at a period sufficiently distant from the +Upper Silurian, in which the first Elasmobranchs and Ganoids occur, to +allow of the evolution of such fishes as these from a Vertebrate as +simple as the _Amphioxus,_ I can only repeat that it is appalling to +speculate upon the extent to which that origin must have preceded the +epoch of the first recorded appearance of vertebrate life. + + +Such is the further commentary which I have to offer upon the statement +of the chief results of palaeontology which I formerly ventured to lay +before you. + +But the growth of knowledge in the interval makes me conscious of an +omission of considerable moment in that statement, inasmuch as it +contains no reference to the bearings of palaeontology upon the theory of +the distribution of life; nor takes note of the remarkable manner in +which the facts of distribution, in present and past times, accord with +the doctrine of evolution, especially in regard to land animals. + +That connection between palaeontology and geology and the present +distribution of terrestrial animals, which so strikingly impressed Mr. +Darwin, thirty years ago, as to lead him to speak of a "law of succession +of types," and of the wonderful relationship on the same continent +between the dead and the living, has recently received much elucidation +from the researches of Gaudry, of Rutimeyer, of Leidy, and of Alphonse +Milne-Edwards, taken in connection with the earlier labours of our +lamented colleague Falconer; and it has been instructively discussed in +the thoughtful and ingenious work of Mr. Andrew Murray "On the +Geographical Distribution of Mammals."[5] + +[Footnote 5: The paper "On the Form and Distribution of the Landtracts +during the Secondary and Tertiary Periods respectively; and on the Effect +upon Animal Life which great Changes in Geographical Configuration have +probably produced," by Mr. Searles V. Wood, jun., which was published in +the _Philosophical Magazine_, in 1862, was unknown to me when this +Address was written. It is well worthy of the most careful study.] + +I propose to lay before you, as briefly as I can, the ideas to which a +long consideration of the subject has given rise in my mind. + +If the doctrine of evolution is sound, one of its immediate consequences +clearly is, that the present distribution of life upon the globe is the +product of two factors, the one being the distribution which obtained in +the immediately preceding epoch, and the other the character and the +extent of the changes which have taken place in physical geography +between the one epoch and the other; or, to put the matter in another +way, the Fauna and Flora of any given area, in any given epoch, can +consist only of such forms of life as are directly descended from those +which constituted the Fauna and Flora of the same area in the immediately +preceding epoch, unless the physical geography (under which I include +climatal conditions) of the area has been so altered as to give rise to +immigration of living forms from some other area. + +The evolutionist, therefore, is bound to grapple with the following +problem whenever it is clearly put before him:--Here are the Faunae of the +same area during successive epochs. Show good cause for believing either +that these Faunae have been derived from one another by gradual +modification, or that the Faunae have reached the area in question by +migration from some area in which they have undergone their development. + +I propose to attempt to deal with this problem, so far as it is +exemplified by the distribution of the terrestrial _Vertebrata_, and I +shall endeavour to show you that it is capable of solution in a sense +entirely favourable to the doctrine of evolution. + +I have elsewhere[6] stated at length the reasons which lead me to +recognise four primary distributional provinces for the terrestrial +_Vertebrata_ in the present world, namely,--first, the _Novozelanian_, or +New-Zealand province; secondly, the _Australian_ province, including +Australia, Tasmania, and the Negrito Islands; thirdly, _Austro-Columbia_, +or South America _plus_ North America as far as Mexico; and fourthly, the +rest of the world, or _Arctogoea_, in which province America north of +Mexico constitutes one sub-province, Africa south of the Sahara a second, +Hindostan a third, and the remainder of the Old World a fourth. + +[Footnote 6: "On the Classification and Distribution of the +Alectoromorphoe;" _Proceedings of the Zoological Society_, 1868.] + +Now the truth which Mr. Darwin perceived and promulgated as "the law of +the succession of types" is, that, in all these provinces, the animals +found in Pliocene or later deposits are closely affined to those which +now inhabit the same provinces; and that, conversely, the forms +characteristic of other provinces are absent. North and South America, +perhaps, present one or two exceptions to the last rule, but they are +readily susceptible of explanation. Thus, in Australia, the later +Tertiary mammals are marsupials (possibly with the exception of the Dog +and a Rodent or two, as at present). In Austro-Columbia, the later +Tertiary fauna exhibits numerous and varied forms of Platyrrhine Apes, +Rodents, Cats, Dogs, Stags, _Edentata_, and Opossums; but, as at present, +no Catarrhine Apes, no Lemurs, no _Insectivora_, Oxen, Antelopes, +Rhinoceroses, nor _Didelphia_ other than Opossums. And in the widespread +Arctogaeal province, the Pliocene and later mammals belong to the same +groups as those which now exist in the province. The law of succession of +types, therefore, holds good for the present epoch as compared with its +predecessor. Does it equally well apply to the Pliocene fauna when we +compare it with that of the Miocene epoch? By great good fortune, an +extensive mammalian fauna of the latter epoch has now become known, in +four very distant portions of the Arctogaeal province which do not differ +greatly in latitude. Thus Falconer and Cautley have made known the fauna +of the sub-Himalayas and the Perim Islands; Gaudry that of Attica; many +observers that of Central Europe and France; and Leidy that of Nebraska, +on the eastern flank of the Rocky Mountains. The results are very +striking. The total Miocene fauna comprises many genera and species of +Catarrhine Apes, of Bats, of _Insectivora_; of Arctogaeal types of +_Rodentia_; of _Proboscidea_; of equine, rhinocerotic, and tapirine +quadrupeds; of cameline, bovine, antilopine, cervine, and traguline +Ruminants; of Pigs and Hippopotamuses; of _Viverridoe_ and _Hyoenidoe_ +among other _Carnivora_; with _Edentata_ allied to the Aretogaeal +_Oryeteropus_ and _Manis_, and not to the Austro-Columbian Edentates. The +only type present in the Miocene, but absent in the existing, fauna of +Eastern Arctogaea, is that of the _Didelphidoe_, which, however, remains +in North America. + +But it is very remarkable that while the Miocene fauna of the Arctogaeal +province, as a whole, is of the same character as the existing fauna of +the same province, as a whole, the component elements of the fauna were +differently associated. In the Miocene epoch, North America possessed +Elephants, Horses, Rhinoceroses, and a great number and variety of +Ruminants and Pigs, which are absent in the present indigenous fauna; +Europe had its Apes, Elephants, Rhinoceroses, Tapirs, Musk-deer, +Giraffes, Hyaenas, great Cats, Edentates, and Opossum-like Marsupials, +which have equally vanished from its present fauna; and in Northern +India, the African types of Hippopotamuses, Giraffes, and Elephants were +mixed up with what are now the Asiatic types of the latter, and with +Camels, and Semnopithecine and Pithecine Apes of no less distinctly +Asiatic forms. + +In fact the Miocene mammalian fauna of Europe and the Himalayan regions +contains, associated together, the types which are at present separately +located in the South-African and Indian sub-provinces of Arctogaea. Now +there is every reason to believe, on other grounds, that both Hindostan, +south of the Ganges, and Africa, south of the Sahara, were separated by a +wide sea from Europe and North Asia during the Middle and Upper Eocene +epochs. Hence it becomes highly probable that the well-known +similarities, and no less remarkable differences between the present +Faunae of India and South Africa have arisen in some such fashion as the +following. Some time during the Miocene epoch, possibly when the +Himalayan chain was elevated, the bottom of the nummulitic sea was +upheaved and converted into dry land, in the direction of a line +extending from Abyssinia to the mouth of the Ganges. By this means, the +Dekhan on the one hand, and South Africa on the other, became connected +with the Miocene dry land and with one another. The Miocene mammals +spread gradually over this intermediate dry land; and if the condition of +its eastern and western ends offered as wide contrasts as the valleys of +the Ganges and Arabia do now, many forms which made their way into Africa +must have been different from those which reached the Dekhan, while +others might pass into both these sub-provinces. + +That there was a continuity of dry land between Europe and North America +during the Miocene epoch, appears to me to be a necessary consequence of +the fact that many genera of terrestrial mammals, such as _Castor, +Hystrix, Elephas, Mastodon, Equus, Hipparion, Anchitherium, Rhinoceros, +Cervus, Amphicyon, Hyoenarctos_, and _Machairodus_, are common to the +Miocene formations of the two areas, and have as yet been found (except +perhaps _Anchitherium_) in no deposit of earlier age. Whether this +connection took place by the east, or by the west, or by both sides of +the Old World, there is at present no certain evidence, and the question +is immaterial to the present argument; but, as there are good grounds for +the belief that the Australian province and the Indian and South-African +sub-provinces were separated by sea from the rest of Arctogaea before the +Miocene epoch, so it has been rendered no less probable, by the +investigations of Mr. Carrick Moore and Professor Duncan, that Austro- +Columbia was separated by sea from North America during a large part of +the Miocene epoch. + +It is unfortunate that we have no knowledge of the Miocene mammalian +fauna of the Australian and Austro-Columbian provinces; but, seeing that +not a trace of a Platyrrhine Ape, of a Procyonine Carnivore, of a +characteristically South-American Rodent, of a Sloth, an Armadillo, or an +Ant-eater has yet been found in Miocene deposits of Arctogaea, I cannot +doubt that they already existed in the Miocene Austro-Columbian province. + +Nor is it less probable that the characteristic types of Australian +Mammalia were already developed in that region in Miocene times. + +But Austro-Columbia presents difficulties from which Australia is free; +_Cantelidoe_ and _Tapirdoe_ are now indigenous in South America as they +are in Arctogaea; and, among the Pliocene Austro-Columbian mammals, the +Arctogaeal genera _Equus, Mastodon,_ and _Machairodus_ are numbered. Are +these Postmiocene immigrants, or Praemiocene natives? + +Still more perplexing are the strange and interesting forms _Toxodon, +Macrauchenia, Typotherium_, and a new Anoplotherioid mammal +(_Homalodotherhon_) which Dr. Cunningham sent over to me some time ago +from Patagonia. I confess I am strongly inclined to surmise that these +last, at any rate, are remnants of the population of Austro-Columbia +before the Miocene epoch, and were not derived from Arctogaea by way of +the north and east. + +The fact that this immense fauna of Miocene Arctogaea is now fully and +richly represented only in India and in South Africa, while it is shrunk +and depauperised in North Asia, Europe, and North America, becomes at +once intelligible, if we suppose that India and South Africa had but a +scanty mammalian population before the Miocene immigration, while the +conditions were highly favourable to the new comers. It is to be supposed +that these new regions offered themselves to the Miocene Ungulates, as +South America and Australia offered themselves to the cattle, sheep, and +horses of modern colonists. But, after these great areas were thus +peopled, came the Glacial epoch, during which the excessive cold, to say +nothing of depression and ice-covering, must have almost depopulated all +the northern parts of Arctogaea, destroying all the higher mammalian +forms, except those which, like the Elephant and Rhinoceros, could adjust +their coats to the altered conditions. Even these must have been driven +away from the greater part of the area; only those Miocene mammals which +had passed into Hindostan and into South Africa would escape decimation +by such changes in the physical geography of Arctogaea. And when the +northern hemisphere passed into its present condition, these lost tribes +of the Miocene Fauna were hemmed by the Himalayas, the Sahara, the Red +Sea, and the Arabian deserts, within their present boundaries. + +Now, on the hypothesis of evolution, there is no sort of difficulty in +admitting that the differences between the Miocene forms of the mammalian +Fauna and those which exist at present are the results of gradual +modification; and, since such differences in distribution as obtain are +readily explained by the changes which have taken place in the physical +geography of the world since the Miocene epoch, it is clear that the +result of the comparison of the Miocene and present Faunae is distinctly +in favour of evolution. Indeed I may go further. I may say that the +hypothesis of evolution explains the facts of Miocene, Pliocene, and +Recent distribution, and that no other supposition even pretends to +account for them. It is, indeed, a conceivable supposition that every +species of Rhinoceros and every species of Hyaena, in the long succession +of forms between the Miocene and the present species, was separately +constructed out of dust, or out of nothing, by supernatural power; but +until I receive distinct evidence of the fact, I refuse to run the risk +of insulting any sane man by supposing that he seriously holds such a +notion. + +Let us now take a step further back in time, and inquire into the +relations between the Miocene Fauna and its predecessor of the Upper +Eocene formation. + +Here it is to be regretted that our materials for forming a judgment are +nothing to be compared in point of extent or variety with those which are +yielded by the Miocene strata. However, what we do know of this Upper +Eocene Fauna of Europe gives sufficient positive information to enable us +to draw some tolerably safe inferences. It has yielded representatives of +_Insectivora_, of _Cheiroptera_, of _Rodentia_, of _Carnivora_, of +artiodactyle and perissodactyle _Ungulata_, and of opossum-like +Marsupials. No Australian type of Marsupial has been discovered in the +Upper Eocene strata, nor any Edentate mammal. The genera (except perhaps +in the case of some of the _Insectivora, Cheiroptera_, and _Rodentia_) +are different from those of the Miocene epoch, but present a remarkable +general similarity to the Miocene and recent genera. In several cases, as +I have already shown, it has now been clearly made out that the relation +between the Eocene and Miocene forms is such that the Eocene form is the +less specialised; while its Miocene ally is more so, and the +specialisation reaches its maximum in the recent forms of the same type. + +So far as the Upper Eocene and the Miocene Mammalian Faunae are +comparable, their relations are such as in no way to oppose the +hypothesis that the older are the progenitors of the more recent forms, +while, in some cases, they distinctly favour that hypothesis. The period +in tine and the changes in physical geography represented by the +nummulitic deposits are undoubtedly very great, while the remains of +Middle Eocene and Older Eocene Mammals are comparatively few. The general +facies of the Middle Eocene Fauna, however, is quite that of the Upper. +The Older Eocene pre-nummulitic mammalian Fauna contains Bats, two genera +of _Carivora_, three genera of _Ungulata_ (probably all perissodactyle), +and a didelphid Marsupial; all these forms, except perhaps the Bat and +the Opossum, belong to genera which are not known to occur out of the +Lower Eocene formation. The _Coryphodon_ appears to have been allied to +the Miocene and later Tapirs, while _Pliolophus_, in its skull and +dentition, curiously partakes of both artiodactyle and perissodactyle +characters; the third trochanter upon its femur, and its three-toed hind +foot, however, appear definitely to fix its position in the latter +division. + +There is nothing, then, in what is known of the older Eocene mammals of +the Arctogaeal province to forbid the supposition that they stood in an +ancestral relation to those of the Calcaire Grossier and the Gypsum of +the Paris basin, and that our present fauna, therefore, is directly +derived from that which already existed in Arctogaea at the commencement +of the Tertiary period. But if we now cross the frontier between the +Cainozoic and the Mesozoic faunae, as they are preserved within the +Arctogaeal area, we meet with an astounding change, and what appears to be +a complete and unmistakable break in the line of biological continuity. + +Among the twelve or fourteen species of _Mammalia_ which are said to have +been found in the Purbecks, not one is a member of the orders +_Cheiroptera, Rodentia, Ungulata_, or _Carnivora_, which are so well +represented in the Tertiaries. No _Insectivora_ are certainly known, nor +any opossum-like Marsupials. Thus there is a vast negative difference +between the Cainozoic and the Mesozoic mammalian faunae of Europe. But +there is a still more important positive difference, inasmuch as all +these Mammalia appear to be Marsupials belonging to Australian groups, +and thus appertaining to a different distributional province from the +Eocene and Miocene marsupials, which are Austro-Columbian. So far as the +imperfect materials which exist enable a judgment to be formed, the same +law appears to have held good for all the earlier Mesozoic _Mammalia_. Of +the Stonesfield slate mammals, one, _Amphitherium_, has a definitely +Australian character; one, _Phascolotherium_, may be either Dasyurid or +Didelphine; of a third, _Stereognathus_, nothing can at present be said. +The two mammals of the Trias, also, appear to belong to Australian +groups. + +Every one is aware of the many curious points of resemblance between the +marine fauna of the European Mesozoic rocks and that which now exists in +Australia. But if there was this Australian facies about both the +terrestrial and the marine faunae of Mesozoic Europe, and if there is this +unaccountable and immense break between the fauna of Mesozoic and that of +Tertiary Europe, is it not a very obvious suggestion that, in the +Mesozoic epoch, the Australian province included Europe, and that the +Arctogaeal province was contained within other limits? The Arctogaeal +province is at present enormous, while the Australian is relatively +small. Why should not these proportions have been different during the +Mesozoic epoch? + +Thus I am led to think that by far the simplest and most rational mode of +accounting for the great change which took place in the living +inhabitants of the European area at the end of the Mesozoic epoch, is the +supposition that it arose from a vast alteration of the physical +geography of the globe; whereby an area long tenanted by Cainozoic forms +was brought into such relations with the European area that migration +from the one to the other became possible, and took place on a great +scale. + +This supposition relieves us, at once, from the difficulty in which we +were left, some time ago, by the arguments which I used to demonstrate +the necessity of the existence of all the great types of the Eocene epoch +in some antecedent period. + +It is this Mesozoic continent (which may well have lain in the +neighbourhood of what are now the shores of the North Pacific Ocean) +which I suppose to have been occupied by the Mesozoic _Monodelphia_; and +it is in this region that I conceive they must have gone through the long +series of changes by which they were specialised into the forms which we +refer to different orders. I think it very probable that what is now +South America may have received the characteristic elements of its +mammalian fauna during the Mesozoic epoch; and there can be little doubt +that the general nature of the change which took place at the end of the +Mesozoic epoch in Europe was the upheaval of the eastern and northern +regions of the Mesozoic sea-bottom into a westward extension of the +Mesozoic continent, over which the mammalian fauna, by which it was +already peopled, gradually spread. This invasion of the land was prefaced +by a previous invasion of the Cretaceous sea by modern forms of mollusca +and fish. + +It is easy to imagine how an analogous change might come about in the +existing world. There is, at present, a great difference between the +fauna of the Polynesian Islands and that of the west coast of America. +The animals which are leaving their spoils in the deposits now forming in +these localities are widely different. Hence, if a gradual shifting of +the deep sea, which at present bars migration between the easternmost of +these islands and America, took place to the westward, while the American +side of the sea-bottom was gradually upheaved, the palaeontologist of the +future would find, over the Pacific area, exactly such a change as I am +supposing to have occurred in the North-Atlantic area at the close of the +Mesozoic period. An Australian fauna would be found underlying an +American fauna, and the transition from the one to the other would be as +abrupt as that between the Chalk and lower Tertiaries; and as the +drainage-area of the newly formed extension of the American continent +gave rise to rivers and lakes, the mammals mired in their mud would +differ from those of like deposits on the Australian side, just as the +Eocene mammals differ from those of the Purbecks. + +How do similar reasonings apply to the other great change of life--that +which took place at the end of the Palaeozoic period? + +In the Triassic epoch, the distribution of the dry land and of +terrestrial vertebrate life appears to have been, generally, similar to +that which existed in the Mesozoic epoch; so that the Triassic continents +and their faunae seem to be related to the Mesozoic lands and their faunae, +just as those of the Miocene epoch are related to those of the present +day. In fact, as I have recently endeavoured to prove to the Society, +there was an Arctogaeal continent and an Arctogaeal province of +distribution in Triassic times as there is now; and the _Sauropsida_ and +_Marsupialia_ which constituted that fauna were, I doubt not, the +progenitors of the _Sauropsida_ and _Marsupialia_ of the whole Mesozoic +epoch. + +Looking at the present terrestrial fauna of Australia, it appears to me +to be very probable that it is essentially a remnant of the fauna of the +Triassic, or even of an earlier, age[7] in which case Australia must at +that time have been in continuity with the Arctogaeal continent. + +[Footnote 7: Since this Address was read, Mr. Krefft has sent us news of +the discovery in Australia of a freshwater fish of strangely Palaeozoic +aspect, and apparently a Ganoid intermediate between _Dipterus_ and +_Lepidosiren_. [The now well-known _Ceratodus_. 1894.]] + +But now comes the further inquiry, Where was the highly differentiated +Sauropsidan fauna of the Trias in Palaeozoic times? The supposition that +the Dinosaurian, Crocodilian, Dicynodontian, and to Plesiosaurian types +were suddenly created at the end of the Permian epoch may be dismissed, +without further consideration, as a monstrous and unwarranted assumption. +The supposition that all these types were rapidly differentiated out of +_Lacertilia_ in the time represented by the passage from the Palaeozoic to +the Mesozoic formation, appears to me to be hardly more credible, to say +nothing of the indications of the existence of Dinosaurian forms in the +Permian rocks which have already been obtained. + +For my part, I entertain no sort of doubt that the Reptiles, Birds, and +Mammals of the Trias are the direct descendants of Reptiles, Birds, and +Mammals which existed in the latter part of the Palaeozoic epoch, but not +in any area of the present dry land which has yet been explored by the +geologist. + +This may seem a bold assumption, but it will not appear unwarrantable to +those who reflect upon the very small extent of the earth's surface which +has hitherto exhibited the remains of the great Mammalian fauna of the +Eocene times. In this respect, the Permian land Vertebrate fauna appears +to me to be related to the Triassic much as the Eocene is to the Miocene. +Terrestrial reptiles have been found in Permian rocks only in three +localities; in some spots of France, and recently of England, and over a +more extensive area in Germany. Who can suppose that the few fossils yet +found in these regions give any sufficient representation of the Permian +fauna? + +It may be said that the Carboniferous formations demonstrate the +existence of a vast extent of dry land in the present dry-land area, and +that the supposed terrestrial Palaeozoic Vertebrate Fauna ought to have +left its remains in the Coal-measures, especially as there is now reason +to believe that much of the coal was formed by the accumulation of spores +and sporangia on dry land. But if we consider the matter more closely, I +think that this apparent objection loses its force. It is clear that, +during the Carboniferous epoch, the vast area of land which is now +covered by Coal-measures must have been undergoing a gradual depression. +The dry land thus depressed must, therefore, have existed, as such, +before the Carboniferous epoch--in other words, in Devonian times--and +its terrestrial population may never have been other than such as existed +during the Devonian, or some previous epoch, although much higher forms +may have been developed elsewhere. + +Again, let me say that I am making no gratuitous assumption of +inconceivable changes. It is clear that the enormous area of Polynesia +is, on the whole, an area over which depression has taken place to an +immense extent; consequently a great continent, or assemblage of +subcontinental masses of land must have existed at some former time, and +that at a recent period, geologically speaking, in the area of the +Pacific. But if that continent had contained Mammals, some of them must +have remained to tell the tale; and as it is well known that these +islands have no indigenous _Mammalia_, it is safe to assume that none +existed. Thus, midway between Australia and South America, each of which +possesses an abundant and diversified mammalian fauna, a mass of land, +which may have been as large as both put together, must have existed +without a mammalian inhabitant. Suppose that the shores of this great +land were fringed, as those of tropical Australia are now, with belts of +mangroves, which would extend landwards on the one side, and be buried +beneath littoral deposits on the other side, as depression went on; and +great beds of mangrove lignite might accumulate over the sinking land. +Let upheaval of the whole now take place, in such a manner as to bring +the emerging land into continuity with the South-American or Australian +continent, and, in course of time, it would be peopled by an extension of +the fauna of one of these two regions--just as I imagine the European +Permian dry land to have been peopled. + +I see nothing whatever against the supposition that distributional +provinces of terrestrial life existed in the Devonian epoch, inasmuch as +M. Barrande has proved that they existed much earlier. I am aware of no +reason for doubting that, as regards the grades of terrestrial life +contained in them, one of these may have been related to another as New +Zealand is to Australia, or as Australia is to India, at the present day. +Analogy seems to me to be rather in favour of, than against, the +supposition that while only Ganoid fishes inhabited the fresh waters of +our Devonian land, _Amphibia_ and _Reptilia_, or even higher forms, may +have existed, though we have not yet found them. The earliest +Carboniferous _Amphibia_ now known, such as _Anthracosaurus_, are so +highly specialised that I can by no means conceive that they have been +developed out of piscine forms in the interval between the Devonian and +the Carboniferous periods, considerable as that is. And I take refuge in +one of two alternatives: either they existed in our own area during the +Devonian epoch and we have simply not yet found them; or they formed part +of the population of some other distributional province of that day, and +only entered our area by migration at the end of the Devonian epoch. +Whether _Reptilia_ and _Mammalia_ existed along with them is to me, at +present, a perfectly open question, which is just as likely to receive an +affirmative as a negative answer from future inquirers. + +Let me now gather together the threads of my argumentation into the form +of a connected hypothetical view of the manner in which the distribution +of living and extinct animals has been brought about. + +I conceive that distinct provinces of the distribution of terrestrial +life have existed since the earliest period at which that life is +recorded, and possibly much earlier; and I suppose, with Mr. Darwin, that +the progress of modification of terrestrial forms is more rapid in areas +of elevation than in areas of depression. I take it to be certain that +Labyrinthodont _Amphibia_ existed in the distributional province which +included the dry land depressed during the Carboniferous epoch; and I +conceive that, in some other distributional provinces of that day, which +remained in the condition of stationary or of increasing dry land, the +various types of the terrestrial _Sauropsida_ and of the _Mammalia_ were +gradually developing. + +The Permian epoch marks the commencement of a new movement of upheaval in +our area, which dry land existed in North America, Europe, Asia, and +Africa, as it does now. Into this great new continental area the Mammals, +Birds, and Reptiles developed during the Palaeozoic epoch spread, and +formed the great Triassic Arctogaeal province. But, at the end of the +Triassic period, the movement of depression recommenced in our area, +though it was doubtless balanced by elevation elsewhere; modification and +development, checked in the one province, went on in that "elsewhere"; +and the chief forms of Mammals, Birds and Reptiles, as we know them, were +evolved and peopled the Mesozoic continent. I conceive Australia to have +become separated from the continent as early as the end of the Triassic +epoch, or not much later. The Mesozoic continent must, I conceive, have +lain to the east, about the shores of the North Pacific and Indian +Oceans; and I am inclined to believe that it continued along the eastern +side of the Pacific area to what is now the province of Austro-Columbia, +the characteristic fauna of which is probably a remnant of the population +of the latter part of this period. + +Towards the latter part of the Mesozoic period the movement of upheaval +around the shores of the Atlantic once more recommenced, and was very +probably accompanied by a depression around those of the Pacific. The +Vertebrate fauna elaborated in the Mesozoic continent moved westward and +took possession of the new lands, which gradually increased in extent up +to, and in some directions after, the Miocene epoch. + +It is in favour of this hypothesis, I think, that it is consistent with +the persistence of a general uniformity in the positions of the great +masses of land and water. From the Devonian period, or earlier, to the +present day, the four great oceans, Atlantic, Pacific, Arctic, and +Antarctic, may have occupied their present positions, and only their +coasts and channels of communication have undergone an incessant +alteration. And, finally, the hypothesis I have put before you requires +no supposition that the rate of change in organic life has been either +greater or less in ancient times than it is now; nor any assumption, +either physical or biological, which has not its justification in +analogous phenomena of existing nature. + +I have now only to discharge the last duty of my office, which is to +thank you, not only for the patient attention with which you have +listened to me so long to-day, but also for the uniform kindness with +which, for the past two years, you have rendered my endeavours to perform +the important, and often laborious, functions of your President a +pleasure instead of a burden. + + + + + +End of the Project Gutenberg EBook of Discourses, by Thomas H. Huxley + +*** END OF THE PROJECT GUTENBERG EBOOK 10060 *** diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..146ce59 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #10060 (https://www.gutenberg.org/ebooks/10060) diff --git a/old/10060-8.txt b/old/10060-8.txt new file mode 100644 index 0000000..e987cfd --- /dev/null +++ b/old/10060-8.txt @@ -0,0 +1,9956 @@ +The Project Gutenberg EBook of Discourses, by Thomas H. Huxley + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Discourses + Biological and Geological Essays + +Author: Thomas H. Huxley + +Release Date: November 12, 2003 [EBook #10060] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK DISCOURSES *** + + + + +Produced by Imran Ghory, Stan Goodman, +Richard Prairie and PG Distributed Proofreaders + + + + + DISCOURSES: + + BIOLOGICAL & GEOLOGICAL + + ESSAYS + + BY + + THOMAS H. HUXLEY + + 1894 + + + +PREFACE + + +The contents of the present volume, with three exceptions, are either +popular lectures, or addresses delivered to scientific bodies with which +I have been officially connected. I am not sure which gave me the more +trouble. For I have not been one of those fortunate persons who are able +to regard a popular lecture as a mere _hors d'oeuvre_, unworthy of being +ranked among the serious efforts of a philosopher; and who keep their +fame as scientific hierophants unsullied by attempts--at least of the +successful sort--to be understanded of the people. + +On the contrary, I found that the task of putting the truths learned in +the field, the laboratory and the museum, into language which, without +bating a jot of scientific accuracy shall be generally intelligible, +taxed such scientific and literary faculty as I possessed to the +uttermost; indeed my experience has furnished me with no better +corrective of the tendency to scholastic pedantry which besets all those +who are absorbed in pursuits remote from the common ways of men, and +become habituated to think and speak in the technical dialect of their +own little world, as if there were no other. + +If the popular lecture thus, as I believe, finds one moiety of its +justification in the self-discipline of the lecturer, it surely finds the +other half in its effect on the auditory. For though various sadly +comical experiences of the results of my own efforts have led me to +entertain a very moderate estimate of the purely intellectual value of +lectures; though I venture to doubt if more than one in ten of an average +audience carries away an accurate notion of what the speaker has been +driving at; yet is that not equally true of the oratory of the hustings, +of the House of Commons, and even of the pulpit? + +Yet the children of this world are wise in their generation; and both the +politician and the priest are justified by results. The living voice has +an influence over human action altogether independent of the intellectual +worth of that which it utters. Many years ago, I was a guest at a great +City dinner. A famous orator, endowed with a voice of rare flexibility +and power; a born actor, ranging with ease through every part, from +refined comedy to tragic unction, was called upon to reply to a toast. +The orator was a very busy man, a charming conversationalist and by no +means despised a good dinner; and, I imagine, rose without having given a +thought to what he was going to say. The rhythmic roll of sound was +admirable, the gestures perfect, the earnestness impressive; nothing was +lacking save sense and, occasionally, grammar. When the speaker sat down +the applause was terrific and one of my neighbours was especially +enthusiastic. So when he had quieted down, I asked him what the orator +had said. And he could not tell me. + +That sagacious person John Wesley, is reported to have replied to some +one who questioned the propriety of his adaptation of sacred words to +extremely secular airs, that he did not see why the Devil should be left +in possession of all the best tunes. And I do not see why science should +not turn to account the peculiarities of human nature thus exploited by +other agencies: all the more because science, by the nature of its being, +cannot desire to stir the passions, or profit by the weaknesses, of human +nature. The most zealous of popular lecturers can aim at nothing more +than the awakening of a sympathy for abstract truth, in those who do not +really follow his arguments; and of a desire to know more and better in +the few who do. + +At the same time it must be admitted that the popularization of science, +whether by lecture or essay, has its drawbacks. Success in this +department has its perils for those who succeed. The "people who fail" +take their revenge, as we have recently had occasion to observe, by +ignoring all the rest of a man's work and glibly labelling him a more +popularizer. If the falsehood were not too glaring, they would say the +same of Faraday and Helmholtz and Kelvin. + +On the other hand, of the affliction caused by persons who think that +what they have picked up from popular exposition qualifies them for +discussing the great problems of science, it may be said, as the Radical +toast said of the power of the Crown in bygone days, that it "has +increased, is increasing, and ought to be diminished." The oddities of +"English as she is spoke" might be abundantly paralleled by those of +"Science as she is misunderstood" in the sermon, the novel, and the +leading article; and a collection of the grotesque travesties of +scientific conceptions, in the shape of essays on such trifles as "the +Nature of Life" and the "Origin of All Things," which reach me, from time +to time, might well be bound up with them. + + +The tenth essay in this volume unfortunately brought me, I will not say +into collision, but into a position of critical remonstrance with regard +to some charges of physical heterodoxy, brought by my distinguished +friend Lord Kelvin, against British Geology. As President of the +Geological Society of London at that time (1869), I thought I might +venture to plead that we were not such heretics as we seemed to be; and +that, even if we were, recantation would not affect the question of +evolution. + +I am glad to see that Lord Kelvin has just reprinted his reply to my +plea,[1] and I refer the reader to it. I shall not presume to question +anything, that on such ripe consideration, Lord Kelvin has to say upon +the physical problems involved. But I may remark that no one can have +asserted more strongly than I have done, the necessity of looking to +physics and mathematics, for help in regard to the earliest history of +the globe. (See pp. 108 and 109 of this volume.) + +[Footnote 1: _Popular Lectures and Addresses._ II. Macmillan and Co. +1894.] + +And I take the opportunity of repeating the opinion, that, whether what +we call geological time has the lower limit assigned to it by Lord +Kelvin, or the higher assumed by other philosophers; whether the germs of +all living things have originated in the globe itself, or whether they +have been imported on, or in, meteorites from without, the problem of the +origin of those successive Faunae and Florae of the earth, the existence of +which is fully demonstrated by paleontology remains exactly where it was. + +For I think it will be admitted, that the germs brought to us by +meteorites, if any, were not ova of elephants, nor of crocodiles; not +cocoa-nuts nor acorns; not even eggs of shell-fish and corals; but only +those of the lowest forms of animal and vegetable life. Therefore, since +it is proved that, from a very remote epoch of geological time, the earth +has been peopled by a continual succession of the higher forms of animals +and plants, these either must have been created, or they have arisen by +evolution. And in respect of certain groups of animals, the well- +established facts of paleontology leave no rational doubt that they arose +by the latter method. + +In the second place, there are no data whatever, which justify the +biologist in assigning any, even approximately definite, period of time, +either long or short, to the evolution of one species from another by the +process of variation and selection. In the ninth of the following essays, +I have taken pains to prove that the change of animals has gone on at +very different rates in different groups of living beings; that some +types have persisted with little change from the paleozoic epoch till +now, while others have changed rapidly within the limits of an epoch. In +1862 (see below p. 303, 304) in 1863 (vol. II., p. 461) and again in 1864 +(ibid., p. 89-91) I argued, not as a matter of speculation, but, from +paleontological facts, the bearing of which I believe, up to that time, +had not been shown, that any adequate hypothesis of the causes of +evolution must be consistent with progression, stationariness and +retrogression, of the same type at different epochs; of different types +in the same epoch; and that Darwin's hypothesis fulfilled these +conditions. + +According to that hypothesis, two factors are at work, variation and +selection. Next to nothing is known of the causes of the former process; +nothing whatever of the time required for the production of a certain +amount of deviation from the existing type. And, as respects selection, +which operates by extinguishing all but a small minority of variations, +we have not the slightest means of estimating the rapidity with which it +does its work. All that we are justified in saying is that the rate at +which it takes place may vary almost indefinitely. If the famous paint- +root of Florida, which kills white pigs but not black ones, were abundant +and certain in its action, black pigs might be substituted for white in +the course of two or three years. If, on the other hand, it was rare and +uncertain in action, the white pigs might linger on for centuries. + +T.H. HUXLEY. + +HODESLEA, EASTBOURNE, + +_April, 1894._ + + + +CONTENTS + + +I + +ON A PIECE OF CHALK [1868] +(A Lecture delivered to the working men of Norwich during the meeting of +the British Association.) + + +II + +THE PROBLEMS OF THE DEEP SEA [1878] + + +III + +ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. "CHALLENGER" [1875] + + +IV + +YEAST [1871] + + +V + +ON THE FORMATION OF COAL [1870] +(A Lecture delivered at the Philosophical Institute, Bradford.) + + +VI + +ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS +[1876] +(A Friday evening Lecture delivered at the Royal Institution.) + + +VII + +A LOBSTER; OR, THE STUDY OF ZOOLOGY [1861] +(A Lecture delivered at the South Kensington Museum.) + + +VIII + +BIOGENESIS AND ABIOGENESIS [1870] +(The Presidential Address to the Meeting of the British Association for +the Advancement of Science at Liverpool.) + + +IX + +GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE [1862] +(Address to the Geological Society on behalf of the President by one of +the Secretaries.) + + +X + +GEOLOGICAL REFORM [1869] +(Presidential Address to the Geological Society.) + + +XI + +PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION [1870] +(Presidential Address to the Geological Society.) + + + +I + + +ON A PIECE OF CHALK + +[1868] + +If a well were sunk at our feet in the midst of the city of Norwich, the +diggers would very soon find themselves at work in that white substance +almost too soft to be called rock, with which we are all familiar as +"chalk." + +Not only here, but over the whole county of Norfolk, the well-sinker +might carry his shaft down many hundred feet without coming to the end of +the chalk; and, on the sea-coast, where the waves have pared away the +face of the land which breasts them, the scarped faces of the high cliffs +are often wholly formed of the same material. Northward, the chalk may be +followed as far as Yorkshire; on the south coast it appears abruptly in +the picturesque western bays of Dorset, and breaks into the Needles of +the Isle of Wight; while on the shores of Kent it supplies that long line +of white cliffs to which England owes her name of Albion. + +Were the thin soil which covers it all washed away, a curved band of +white chalk, here broader, and there narrower, might be followed +diagonally across England from Lulworth in Dorset, to Flamborough Head in +Yorkshire--a distance of over 280 miles as the crow flies. From this band +to the North Sea, on the east, and the Channel, on the south, the chalk +is largely hidden by other deposits; but, except in the Weald of Kent and +Sussex, it enters into the very foundation of all the south-eastern +counties. + +Attaining, as it does in some places, a thickness of more than a thousand +feet, the English chalk must be admitted to be a mass of considerable +magnitude. Nevertheless, it covers but an insignificant portion of the +whole area occupied by the chalk formation of the globe, much of which +has the same general characters as ours, and is found in detached +patches, some less, and others more extensive, than the English. Chalk +occurs in north-west Ireland; it stretches over a large part of France,-- +the chalk which underlies Paris being, in fact, a continuation of that of +the London basin; it runs through Denmark and Central Europe, and extends +southward to North Africa; while eastward, it appears in the Crimea and +in Syria, and may be traced as far as the shores of the Sea of Aral, in +Central Asia. If all the points at which true chalk occurs were +circumscribed, they would lie within an irregular oval about 3,000 miles +in long diameter--the area of which would be as great as that of Europe, +and would many times exceed that of the largest existing inland sea--the +Mediterranean. + +Thus the chalk is no unimportant element in the masonry of the earth's +crust, and it impresses a peculiar stamp, varying with the conditions to +which it is exposed, on the scenery of the districts in which it occurs. +The undulating downs and rounded coombs, covered with sweet-grassed turf, +of our inland chalk country, have a peacefully domestic and mutton- +suggesting prettiness, but can hardly be called either grand or +beautiful. But on our southern coasts, the wall-sided cliffs, many +hundred feet high, with vast needles and pinnacles standing out in the +sea, sharp and solitary enough to serve as perches for the wary +cormorant, confer a wonderful beauty and grandeur upon the chalk +headlands. And, in the East, chalk has its share in the formation of some +of the most venerable of mountain ranges, such as the Lebanon. + +What is this wide-spread component of the surface of the earth? and +whence did it come? + + +You may think this no very hopeful inquiry. You may not unnaturally +suppose that the attempt to solve such problems as these can lead to no +result, save that of entangling the inquirer in vague speculations, +incapable of refutation and of verification. If such were really the +case, I should have selected some other subject than a "piece of chalk" +for my discourse. But, in truth, after much deliberation, I have been +unable to think of any topic which would so well enable me to lead you to +see how solid is the foundation upon which some of the most startling +conclusions of physical science rest. + +A great chapter of the history of the world is written in the chalk. Few +passages in the history of man can be supported by such an overwhelming +mass of direct and indirect evidence as that which testifies to the truth +of the fragment of the history of the globe, which I hope to enable you +to read, with your own eyes, to-night. Let me add, that few chapters of +human history have a more profound significance for ourselves. I weigh my +words well when I assert, that the man who should know the true history +of the bit of chalk which every carpenter carries about in his breeches- +pocket, though ignorant of all other history, is likely, if he will think +his knowledge out to its ultimate results, to have a truer, and therefore +a better, conception of this wonderful universe, and of man's relation to +it, than the most learned student who is deep-read in the records of +humanity and ignorant of those of Nature. + +The language of the chalk is not hard to learn, not nearly so hard as +Latin, if you only want to get at the broad features of the story it has +to tell; and I propose that we now set to work to spell that story out +together. + +We all know that if we "burn" chalk the result is quicklime. Chalk, in +fact, is a compound of carbonic acid gas, and lime, and when you make it +very hot the carbonic acid flies away and the lime is left. By this +method of procedure we see the lime, but we do not see the carbonic acid. +If, on the other hand, you were to powder a little chalk and drop it into +a good deal of strong vinegar, there would be a great bubbling and +fizzing, and, finally, a clear liquid, in which no sign of chalk would +appear. Here you see the carbonic acid in the bubbles; the lime, +dissolved in the vinegar, vanishes from sight. There are a great many +other ways of showing that chalk is essentially nothing but carbonic acid +and quicklime. Chemists enunciate the result of all the experiments which +prove this, by stating that chalk is almost wholly composed of "carbonate +of lime." + +It is desirable for us to start from the knowledge of this fact, though +it may not seem to help us very far towards what we seek. For carbonate +of lime is a widely-spread substance, and is met with under very various +conditions. All sorts of limestones are composed of more or less pure +carbonate of lime. The crust which is often deposited by waters which +have drained through limestone rocks, in the form of what are called +stalagmites and stalactites, is carbonate of lime. Or, to take a more +familiar example, the fur on the inside of a tea-kettle is carbonate of +lime; and, for anything chemistry tells us to the contrary, the chalk +might be a kind of gigantic fur upon the bottom of the earth-kettle, +which is kept pretty hot below. + +Let us try another method of making the chalk tell us its own history. To +the unassisted eye chalk looks simply like a very loose and open kind of +stone. But it is possible to grind a slice of chalk down so thin that you +can see through it--until it is thin enough, in fact, to be examined with +any magnifying power that may be thought desirable. A thin slice of the +fur of a kettle might be made in the same way. If it were examined +microscopically, it would show itself to be a more or less distinctly +laminated mineral substance, and nothing more. + +But the slice of chalk presents a totally different appearance when +placed under the microscope. The general mass of it is made up of very +minute granules; but, imbedded in this matrix, are innumerable bodies, +some smaller and some larger, but, on a rough average, not more than a +hundredth of an inch in diameter, having a well-defined shape and +structure. A cubic inch of some specimens of chalk may contain hundreds +of thousands of these bodies, compacted together with incalculable +millions of the granules. + +The examination of a transparent slice gives a good notion of the manner +in which the components of the chalk are arranged, and of their relative +proportions. But, by rubbing up some chalk with a brush in water and then +pouring off the milky fluid, so as to obtain sediments of different +degrees of fineness, the granules and the minute rounded bodies may be +pretty well separated from one another, and submitted to microscopic +examination, either as opaque or as transparent objects. By combining the +views obtained in these various methods, each of the rounded bodies may +be proved to be a beautifully-constructed calcareous fabric, made up of a +number of chambers, communicating freely with one another. The chambered +bodies are of various forms. One of the commonest is something like a +badly-grown raspberry, being formed of a number of nearly globular +chambers of different sizes congregated together. It is called +_Globigerina_, and some specimens of chalk consist of little else than +_Globigerinoe_ and granules. Let us fix our attention upon the +_Globigerina_. It is the spoor of the game we are tracking. If we can +learn what it is and what are the conditions of its existence, we shall +see our way to the origin and past history of the chalk. + +A suggestion which may naturally enough present itself is, that these +curious bodies are the result of some process of aggregation which has +taken place in the carbonate of lime; that, just as in winter, the rime +on our windows simulates the most delicate and elegantly arborescent +foliage--proving that the mere mineral water may, under certain +conditions, assume the outward form of organic bodies--so this mineral +substance, carbonate of lime, hidden away in the bowels of the earth, has +taken the shape of these chambered bodies. I am not raising a merely +fanciful and unreal objection. Very learned men, in former days, have +even entertained the notion that all the formed things found in rocks are +of this nature; and if no such conception is at present held to be +admissible, it is because long and varied experience has now shown that +mineral matter never does assume the form and structure we find in +fossils. If any one were to try to persuade you that an oyster-shell +(which is also chiefly composed of carbonate of lime) had crystallized +out of sea-water, I suppose you would laugh at the absurdity. Your +laughter would be justified by the fact that all experience tends to show +that oyster-shells are formed by the agency of oysters, and in no other +way. And if there were no better reasons, we should be justified, on like +grounds, in believing that _Globigerina_ is not the product of anything +but vital activity. + +Happily, however, better evidence in proof of the organic nature of the +_Globigerinoe_ than that of analogy is forthcoming. It so happens that +calcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk, +are being formed, at the present moment, by minute living creatures, +which flourish in multitudes, literally more numerous than the sands of +the sea-shore, over a large extent of that part of the earth's surface +which is covered by the ocean. + +The history of the discovery of these living _Globigerinoe_, and of the +part which they play in rock building, is singular enough. It is a +discovery which, like others of no less scientific importance, has +arisen, incidentally, out of work devoted to very different and +exceedingly practical interests. When men first took to the sea, they +speedily learned to look out for shoals and rocks; and the more the +burthen of their ships increased, the more imperatively necessary it +became for sailors to ascertain with precision the depth of the waters +they traversed. Out of this necessity grew the use of the lead and +sounding line; and, ultimately, marine-surveying, which is the recording +of the form of coasts and of the depth of the sea, as ascertained by the +sounding-lead, upon charts. + +At the same time, it became desirable to ascertain and to indicate the +nature of the sea-bottom, since this circumstance greatly affects its +goodness as holding ground for anchors. Some ingenious tar, whose name +deserves a better fate than the oblivion into which it has fallen, +attained this object by "arming" the bottom of the lead with a lump of +grease, to which more or less of the sand or mud, or broken shells, as +the case might be, adhered, and was brought to the surface. But, however +well adapted such an apparatus might be for rough nautical purposes, +scientific accuracy could not be expected from the armed lead, and to +remedy its defects (especially when applied to sounding in great depths) +Lieut. Brooke, of the American Navy, some years ago invented a most +ingenious machine, by which a considerable portion of the superficial +layer of the sea-bottom can be scooped out and brought up from any depth +to which the lead descends. In 1853, Lieut. Brooke obtained mud from the +bottom of the North Atlantic, between Newfoundland and the Azores, at a +depth of more than 10,000 feet, or two miles, by the help of this +sounding apparatus. The specimens were sent for examination to Ehrenberg +of Berlin, and to Bailey of West Point, and those able microscopists +found that this deep-sea mud was almost entirely composed of the +skeletons of living organisms--the greater proportion of these being just +like the _Globigerinoe_ already known to occur in the chalk. + +Thus far, the work had been carried on simply in the interests of +science, but Lieut. Brooke's method of sounding acquired a high +commercial value, when the enterprise of laying down the telegraph-cable +between this country and the United States was undertaken. For it became +a matter of immense importance to know, not only the depth of the sea +over the whole line along which the cable was to be laid, but the exact +nature of the bottom, so as to guard against chances of cutting or +fraying the strands of that costly rope. The Admiralty consequently +ordered Captain Dayman, an old friend and shipmate of mine, to ascertain +the depth over the whole line of the cable, and to bring back specimens +of the bottom. In former days, such a command as this might have sounded +very much like one of the impossible things which the young Prince in the +Fairy Tales is ordered to do before he can obtain the hand of the +Princess. However, in the months of June and July, 1857, my friend +performed the task assigned to him with great expedition and precision, +without, so far as I know, having met with any reward of that kind. The +specimens or Atlantic mud which he procured were sent to me to be +examined and reported upon.[1] + +[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings in the +North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S. +"Cyclops_." Published by order of the Lords Commissioners of the +Admiralty, 1858. They have since formed the subject of an elaborate +Memoir by Messrs. Parker and Jones, published in the _Philosophical +Transactions_ for 1865.] + +The result of all these operations is, that we know the contours and the +nature of the surface-soil covered by the North Atlantic for a distance +of 1,700 miles from east to west, as well as we know that of any part of +the dry land. It is a prodigious plain--one of the widest and most even +plains in the world. If the sea were drained off, you might drive a +waggon all the way from Valentia, on the west coast of Ireland, to +Trinity Bay, in Newfoundland. And, except upon one sharp incline about +200 miles from Valentia, I am not quite sure that it would even be +necessary to put the skid on, so gentle are the ascents and descents upon +that long route. From Valentia the road would lie down-hill for about 200 +miles to the point at which the bottom is now covered by 1,700 fathoms of +sea-water. Then would come the central plain, more than a thousand miles +wide, the inequalities of the surface of which would be hardly +perceptible, though the depth of water upon it now varies from 10,000 to +15,000 feet; and there are places in which Mont Blanc might be sunk +without showing its peak above water. Beyond this, the ascent on the +American side commences, and gradually leads, for about 300 miles, to the +Newfoundland shore. + +Almost the whole of the bottom of this central plain (which extends for +many hundred miles in a north and south direction) is covered by a fine +mud, which, when brought to the surface, dries into a greyish white +friable substance. You can write with this on a blackboard, if you are so +inclined; and, to the eye, it is quite like very soft, grayish chalk. +Examined chemically, it proves to be composed almost wholly of carbonate +of lime; and if you make a section of it, in the same way as that of the +piece of chalk was made, and view it with the microscope, it presents +innumerable _Globigerinoe_ embedded in a granular matrix. Thus this deep- +sea mud is substantially chalk. I say substantially, because there are a +good many minor differences; but as these have no bearing on the question +immediately before us,--which is the nature of the _Globigerinoe_ of the +chalk,--it is unnecessary to speak of them. + +_Globigerinoe_ of every size, from the smallest to the largest, are +associated together in the Atlantic mud, and the chambers of many are +filled by a soft animal matter. This soft substance is, in fact, the +remains of the creature to which the _Globigerinoe_ shell, or rather +skeleton, owes its existence--and which is an animal of the simplest +imaginable description. It is, in fact, a mere particle of living jelly, +without defined parts of any kind--without a mouth, nerves, muscles, or +distinct organs, and only manifesting its vitality to ordinary +observation by thrusting out and retracting from all parts of its +surface, long filamentous processes, which serve for arms and legs. Yet +this amorphous particle, devoid of everything which, in the higher +animals, we call organs, is capable of feeding, growing, and multiplying; +of separating from the ocean the small proportion of carbonate of lime +which is dissolved in sea-water; and of building up that substance into a +skeleton for itself, according to a pattern which can be imitated by no +other known agency. + +The notion that animals can live and flourish in the sea, at the vast +depths from which apparently living _Globigerinoe_; have been brought up, +does not agree very well with our usual conceptions respecting the +conditions of animal life; and it is not so absolutely impossible as it +might at first sight appear to be, that the _Globigcrinoe_ of the +Atlantic sea-bottom do not live and die where they are found. + +As I have mentioned, the soundings from the great Atlantic plain are +almost entirely made up of _Globigerinoe_, with the granules which have +been mentioned, and some few other calcareous shells; but a small +percentage of the chalky mud--perhaps at most some five per cent. of it-- +is of a different nature, and consists of shells and skeletons composed +of silex, or pure flint. These silicious bodies belong partly to the +lowly vegetable organisms which are called _Diatomaceoe_, and partly to +the minute, and extremely simple, animals, termed _Radiolaria_. It is +quite certain that these creatures do not live at the bottom of the +ocean, but at its surface--where they may be obtained in prodigious +numbers by the use of a properly constructed net. Hence it follows that +these silicious organisms, though they are not heavier than the lightest +dust, must have fallen, in some cases, through fifteen thousand feet of +water, before they reached their final resting-place on the ocean floor. +And considering how large a surface these bodies expose in proportion to +their weight, it is probable that they occupy a great length of time in +making their burial journey from the surface of the Atlantic to the +bottom. + +But if the _Radiolaria_ and Diatoms are thus rained upon the bottom of +the sea, from the superficial layer of its waters in which they pass +their lives, it is obviously possible that the _Globigerinoe_ may be +similarly derived; and if they were so, it would be much more easy to +understand how they obtain their supply of food than it is at present. +Nevertheless, the positive and negative evidence all points the other +way. The skeletons of the full-grown, deep-sea _Globigerinoe_ are so +remarkably solid and heavy in proportion to their surface as to seem +little fitted for floating; and, as a matter of fact, they are not to be +found along with the Diatoms and _Radiolaria_ in the uppermost stratum of +the open ocean. It has been observed, again, that the abundance of +_Globigerinoe_, in proportion to other organisms, of like kind, increases +with the depth of the sea; and that deep-water _Globigerinoe_ are larger +than those which live in shallower parts of the sea; and such facts +negative the supposition that these organisms have been swept by currents +from the shallows into the deeps of the Atlantic. It therefore seems to +be hardly doubtful that these wonderful creatures live and die at the +depths in which they are found.[2] + +[Footnote 2: During the cruise of H.M.S. _Bulldog_, commanded by Sir +Leopold M'Clintock, in 1860, living star-fish were brought up, clinging +to the lowest part of the sounding-line, from a depth of 1,260 fathoms, +midway between Cape Farewell, in Greenland, and the Rockall banks. Dr. +Wallich ascertained that the sea-bottom at this point consisted of the +ordinary _Globigerina_ ooze, and that the stomachs of the star-fishes +were full of _Globigerinoe_. This discovery removes all objections to the +existence of living _Globigerinoe_ at great depths, which are based upon +the supposed difficulty of maintaining animal life under such conditions; +and it throws the burden of proof upon those who object to the +supposition that the _Globigerinoe_ live and die where they are found.] + +However, the important points for us are, that the living _Globigerinoe_ +are exclusively marine animals, the skeletons of which abound at the +bottom of deep seas; and that there is not a shadow of reason for +believing that the habits of the _Globigerinoe_ of the chalk differed +from those of the existing species. But if this be true, there is no +escaping the conclusion that the chalk itself is the dried mud of an +ancient deep sea. + +In working over the soundings collected by Captain Dayman, I was +surprised to find that many of what I have called the "granules" of that +mud were not, as one might have been tempted to think at first, the more +powder and waste of _Globigerinoe_, but that they had a definite form and +size. I termed these bodies "_coccoliths_," and doubted their organic +nature. Dr. Wallich verified my observation, and added the interesting +discovery that, not unfrequently, bodies similar to these "coccoliths" +were aggregated together into spheroids, which lie termed +"_coccospheres_." So far as we knew, these bodies, the nature of which is +extremely puzzling and problematical, were peculiar to the Atlantic +soundings. But, a few years ago, Mr. Sorby, in making a careful +examination of the chalk by means of thin sections and otherwise, +observed, as Ehrenberg had done before him, that much of its granular +basis possesses a definite form. Comparing these formed particles with +those in the Atlantic soundings, he found the two to be identical; and +thus proved that the chalk, like the surroundings, contains these +mysterious coccoliths and coccospheres. Here was a further and most +interesting confirmation, from internal evidence, of the essential +identity of the chalk with modern deep-sea mud. _Globigerinoe_, +coccoliths, and coccospheres are found as the chief constituents of both, +and testify to the general similarity of the conditions under which both +have been formed.[3] + +[Footnote 3: I have recently traced out the development of the +"coccoliths" from a diameter of 1/7000th of an inch up to their largest +size (which is about 1/1000th), and no longer doubt that they are +produced by independent organisms, which, like the _Globigerinoe_, live +and die at the bottom of the sea.] + +The evidence furnished by the hewing, facing, and superposition of the +stones of the Pyramids, that these structures were built by men, has no +greater weight than the evidence that the chalk was built by +_Globigerinoe_; and the belief that those ancient pyramid-builders were +terrestrial and air-breathing creatures like ourselves, is not better +based than the conviction that the chalk-makers lived in the sea. But as +our belief in the building of the Pyramids by men is not only grounded on +the internal evidence afforded by these structures, but gathers strength +from multitudinous collateral proofs, and is clinched by the total +absence of any reason for a contrary belief; so the evidence drawn from +the _Globigerinoe_ that the chalk is an ancient sea-bottom, is fortified +by innumerable independent lines of evidence; and our belief in the truth +of the conclusion to which all positive testimony tends, receives the +like negative justification from the fact that no other hypothesis has a +shadow of foundation. + +It may be worth while briefly to consider a few of these collateral +proofs that the chalk was deposited at the bottom of the sea. The great +mass of the chalk is composed, as we have seen, of the skeletons of +_Globigerinoe_, and other simple organisms, imbedded in granular matter. +Here and there, however, this hardened mud of the ancient sea reveals the +remains of higher animals which have lived and died, and left their hard +parts in the mud, just as the oysters die and leave their shells behind +them, in the mud of the present seas. + +There are, at the present day, certain groups of animals which are never +found in fresh waters, being unable to live anywhere but in the sea. Such +are the corals; those corallines which are called _Polyzoa_; those +creatures which fabricate the lamp-shells, and are called _Brachiopoda_; +the pearly _Nautilus_, and all animals allied to it; and all the forms of +sea-urchins and star-fishes. Not only are all these creatures confined to +salt water at the present day; but, so far as our records of the past go, +the conditions of their existence have been the same: hence, their +occurrence in any deposit is as strong evidence as can be obtained, that +that deposit was formed in the sea. Now the remains of animals of all the +kinds which have been enumerated, occur in the chalk, in greater or less +abundance; while not one of those forms of shell-fish which are +characteristic of fresh water has yet been observed in it. + +When we consider that the remains of more than three thousand distinct +species of aquatic animals have been discovered among the fossils of the +chalk, that the great majority of them are of such forms as are now met +with only in the sea, and that there is no reason to believe that any one +of them inhabited fresh water--the collateral evidence that the chalk +represents an ancient sea-bottom acquires as great force as the proof +derived from the nature of the chalk itself. I think you will now allow +that I did not overstate my case when I asserted that we have as strong +grounds for believing that all the vast area of dry land, at present +occupied by the chalk, was once at the bottom of the sea, as we have for +any matter of history whatever; while there is no justification for any +other belief. + +No less certain it is that the time during which the countries we now +call south-east England, France, Germany, Poland, Russia, Egypt, Arabia, +Syria, were more or less completely covered by a deep sea, was of +considerable duration. We have already seen that the chalk is, in places, +more than a thousand feet thick. I think you will agree with me, that it +must have taken some time for the skeletons of animalcules of a hundredth +of an inch in diameter to heap up such a mass as that. I have said that +throughout the thickness of the chalk the remains of other animals are +scattered. These remains are often in the most exquisite state of +preservation. The valves of the shell-fishes are commonly adherent; the +long spines of some of the sea-urchins, which would be detached by the +smallest jar, often remain in their places. In a word, it is certain that +these animals have lived and died when the place which they now occupy +was the surface of as much of the chalk as had then been deposited; and +that each has been covered up by the layer of _Globigerina_ mud, upon +which the creatures imbedded a little higher up have, in like manner, +lived and died. But some of these remains prove the existence of reptiles +of vast size in the chalk sea. These lived their time, and had their +ancestors and descendants, which assuredly implies time, reptiles being +of slow growth. + +There is more curious evidence, again, that the process of covering up, +or, in other words, the deposit of _Globigerina_ skeletons, did not go on +very fast. It is demonstrable that an animal of the cretaceous sea might +die, that its skeleton might lie uncovered upon the sea-bottom long +enough to lose all its outward coverings and appendages by putrefaction; +and that, after this had happened, another animal might attach itself to +the dead and naked skeleton, might grow to maturity, and might itself die +before the calcareous mud had buried the whole. + +Cases of this kind are admirably described by Sir Charles Lyell. He +speaks of the frequency with which geologists find in the chalk a +fossilized sea-urchin, to which is attached the lower valve of a +_Crania_. This is a kind of shell-fish, with a shell composed of two +pieces, of which, as in the oyster, one is fixed and the other free. + +"The upper valve is almost invariably wanting, though occasionally found +in a perfect state of preservation in the white chalk at some distance. +In this case, we see clearly that the sea-urchin first lived from youth +to age, then died and lost its spines, which were carried away. Then the +young _Crania_ adhered to the bared shell, grew and perished in its turn; +after which, the upper valve was separated from the lower, before the +Echinus became enveloped in chalky mud."[4] + +A specimen in the Museum of Practical Geology, in London, still further +prolongs the period which must have elapsed between the death of the sea- +urchin, and its burial by the _Globigerinoe_. For the outward face of the +valve of a _Crania_, which is attached to a sea-urchin, (_Micraster_), is +itself overrun by an incrusting coralline, which spreads thence over more +or less of the surface of the sea-urchin. It follows that, after the +upper valve of the _Crania_ fell off, the surface of the attached valve +must have remained exposed long enough to allow of the growth of the +whole coralline, since corallines do not live embedded in mud.[4] + +[Footnote 4: _Elements of Geology_, by Sir Charles Lyell, Bart. F.B.S., +p. 23.] + +The progress of knowledge may, one day, enable us to deduce from such +facts as these the maximum rate at which the chalk can have accumulated, +and thus to arrive at the minimum duration of the chalk period. Suppose +that the valve of the _Cronia_ upon which a coralline has fixed itself in +the way just described, is so attached to the sea-urchin that no part of +it is more than an inch above the face upon which the sea-urchin rests. +Then, as the coralline could not have fixed itself, if the _Crania_ had +been covered up with chalk mud, and could not have lived had itself been +so covered, it follows, that an inch of chalk mud could not have +accumulated within the time between the death and decay of the soft parts +of the sea-urchin and the growth of the coralline to the full size which +it has attained. If the decay of the soft parts of the sea-urchin; the +attachment, growth to maturity, and decay of the _Crania_; and the +subsequent attachment and growth of the coralline, took a year (which is +a low estimate enough), the accumulation of the inch of chalk must have +taken more than a year: and the deposit of a thousand feet of chalk must, +consequently, have taken more than twelve thousand years. + +The foundation of all this calculation is, of course, a knowledge of the +length of time the _Crania_ and the coralline needed to attain their full +size; and, on this head, precise knowledge is at present wanting. But +there are circumstances which tend to show, that nothing like an inch of +chalk has accumulated during the life of a _Crania_; and, on any probable +estimate of the length of that life, the chalk period must have had a +much longer duration than that thus roughly assigned to it. + +Thus, not only is it certain that the chalk is the mud of an ancient sea- +bottom; but it is no less certain, that the chalk sea existed during an +extremely long period, though we may not be prepared to give a precise +estimate of the length of that period in years. The relative duration is +clear, though the absolute duration may not be definable. The attempt to +affix any precise date to the period at which the chalk sea began, or +ended, its existence, is baffled by difficulties of the same kind. But +the relative age of the cretaceous epoch may be determined with as great +ease and certainty as the long duration of that epoch. + +You will have heard of the interesting discoveries recently made, in +various parts of Western Europe, of flint implements, obviously worked +into shape by human hands, under circumstances which show conclusively +that man is a very ancient denizen of these regions. It has been proved +that the whole populations of Europe, whose existence has been revealed +to us in this way, consisted of savages, such as the Esquimaux are now; +that, in the country which is now France, they hunted the reindeer, and +were familiar with the ways of the mammoth and the bison. The physical +geography of France was in those days different from what it is now--the +river Somme, for instance, having cut its bed a hundred feet deeper +between that time and this; and, it is probable, that the climate was +more like that of Canada or Siberia, than that of Western Europe. + +The existence of these people is forgotten even in the traditions of the +oldest historical nations. The name and fame of them had utterly vanished +until a few years back; and the amount of physical change which has been +effected since their day renders it more than probable that, venerable as +are some of the historical nations, the workers of the chipped flints of +Hoxne or of Amiens are to them, as they are to us, in point of antiquity. +But, if we assign to these hoar relics of long-vanished generations of +men the greatest age that can possibly be claimed for them, they are not +older than the drift, or boulder clay, which, in comparison with the +chalk, is but a very juvenile deposit. You need go no further than your +own sea-board for evidence of this fact. At one of the most charming +spots on the coast of Norfolk, Cromer, you will see the boulder clay +forming a vast mass, which lies upon the chalk, and must consequently +have come into existence after it. Huge boulders of chalk are, in fact, +included in the clay, and have evidently been brought to the position +they now occupy by the same agency as that which has planted blocks of +syenite from Norway side by side with them. + +The chalk, then, is certainly older than the boulder clay. If you ask how +much, I will again take you no further than the same spot upon your own +coasts for evidence. I have spoken of the boulder clay and drift as +resting upon the chalk. That is not strictly true. Interposed between the +chalk and the drift is a comparatively insignificant layer, containing +vegetable matter. But that layer tells a wonderful history. It is full of +stumps of trees standing as they grew. Fir-trees are there with their +cones, and hazel-bushes with their nuts; there stand the stools of oak +and yew trees, beeches and alders. Hence this stratum is appropriately +called the "forest-bed." + +It is obvious that the chalk must have been upheaved and converted into +dry land, before the timber trees could grow upon it. As the bolls of +some of these trees are from two to three feet in diameter, it is no less +clear that the dry land thus formed remained in the same condition for +long ages. And not only do the remains of stately oaks and well-grown +firs testify to the duration of this condition of things, but additional +evidence to the same effect is afforded by the abundant remains of +elephants, rhinoceroses, hippopotamuses, and other great wild beasts, +which it has yielded to the zealous search of such men as the Rev. Mr. +Gunn. When you look at such a collection as he has formed, and bethink +you that these elephantine bones did veritably carry their owners about, +and these great grinders crunch, in the dark woods of which the forest- +bed is now the only trace, it is impossible not to feel that they are as +good evidence of the lapse of time as the annual rings of the tree +stumps. + +Thus there is a writing upon the wall of cliffs at Cromer, and whoso runs +may read it. It tells us, with an authority which cannot be impeached, +that the ancient sea-bed of the chalk sea was raised up, and remained dry +land, until it was covered with forest, stocked with the great game the +spoils of which have rejoiced your geologists. How long it remained in +that condition cannot be said; but "the whirligig of time brought its +revenges" in those days as in these. That dry land, with the bones and +teeth of generations of long-lived elephants, hidden away among the +gnarled roots and dry leaves of its ancient trees, sank gradually to the +bottom of the icy sea, which covered it with huge masses of drift and +boulder clay. Sea-beasts, such as the walrus, now restricted to the +extreme north, paddled about where birds had twittered among the topmost +twigs of the fir-trees. How long this state of things endured we know +not, but at length it came to an end. The upheaved glacial mud hardened +into the soil of modern Norfolk. Forests grew once more, the wolf and the +beaver replaced the reindeer and the elephant; and at length what we call +the history of England dawned. + +Thus you have, within the limits of your own county, proof that the chalk +can justly claim a very much greater antiquity than even the oldest +physical traces of mankind. But we may go further and demonstrate, by +evidence of the same authority as that which testifies to the existence +of the father of men, that the chalk is vastly older than Adam himself. +The Book of Genesis informs us that Adam, immediately upon his creation, +and before the appearance of Eve, was placed in the Garden of Eden. The +problem of the geographical position of Eden has greatly vexed the +spirits of the learned in such matters, but there is one point respecting +which, so far as I know, no commentator has ever raised a doubt. This is, +that of the four rivers which are said to run out of it, Euphrates and +Hiddekel are identical with the rivers now known by the names of +Euphrates and Tigris. But the whole country in which these mighty rivers +take their origin, and through which they run, is composed of rocks which +are either of the same age as the chalk, or of later date. So that the +chalk must not only have been formed, but, after its formation, the time +required for the deposit of these later rocks, and for their upheaval +into dry land, must have elapsed, before the smallest brook which feeds +the swift stream of "the great river, the river of Babylon," began to +flow. + + +Thus, evidence which cannot be rebutted, and which need not be +strengthened, though if time permitted I might indefinitely increase its +quantity, compels you to believe that the earth, from the time of the +chalk to the present day, has been the theatre of a series of changes as +vast in their amount, as they were slow in their progress. The area on +which we stand has been first sea and then land, for at least four +alternations; and has remained in each of these conditions for a period +of great length. + +Nor have these wonderful metamorphoses of sea into land, and of land into +sea, been confined to one corner of England. During the chalk period, or +"cretaceous epoch," not one of the present great physical features of the +globe was in existence. Our great mountain ranges, Pyrenees, Alps, +Himalayas, Andes, have all been upheaved since the chalk was deposited, +and the cretaceous sea flowed over the sites of Sinai and Ararat. All +this is certain, because rocks of cretaceous, or still later, date have +shared in the elevatory movements which gave rise to these mountain +chains; and may be found perched up, in some cases, many thousand feet +high upon their flanks. And evidence of equal cogency demonstrates that, +though, in Norfolk, the forest-bed rests directly upon the chalk, yet it +does so, not because the period at which the forest grew immediately +followed that at which the chalk was formed, but because an immense lapse +of time, represented elsewhere by thousands of feet of rock, is not +indicated at Cromer. + +I must ask you to believe that there is no less conclusive proof that a +still more prolonged succession of similar changes occurred, before the +chalk was deposited. Nor have we any reason to think that the first term +in the series of these changes is known. The oldest sea-beds preserved to +us are sands, and mud, and pebbles, the wear and tear of rocks which were +formed in still older oceans. + +But, great as is the magnitude of these physical changes of the world, +they have been accompanied by a no less striking series of modifications +in its living inhabitants. All the great classes of animals, beasts of +the field, fowls of the air, creeping things, and things which dwell in +the waters, flourished upon the globe long ages before the chalk was +deposited. Very few, however, if any, of these ancient forms of animal +life were identical with those which now live. Certainly not one of the +higher animals was of the same species as any of those now in existence. +The beasts of the field, in the days before the chalk, were not our +beasts of the field, nor the fowls of the air such as those which the eye +of men has seen flying, unless his antiquity dates infinitely further +back than we at present surmise. If we could be carried back into those +times, we should be as one suddenly set down in Australia before it was +colonized. We should see mammals, birds, reptiles, fishes, insects, +snails, and the like, clearly recognizable as such, and yet not one of +them would be just the same as those with which we are familiar, and many +would be extremely different. + +From that time to the present, the population of the world has undergone +slow and gradual, but incessant, changes. There has been no grand +catastrophe--no destroyer has swept away the forms of life of one period, +and replaced them by a totally new creation: but one species has vanished +and another has taken its place; creatures of one type of structure have +diminished, those of another have increased, as time has passed on. And +thus, while the differences between the living creatures of the time +before the chalk and those of the present day appear startling, if placed +side by side, we are led from one to the other by the most gradual +progress, if we follow the course of Nature through the whole series of +those relics of her operations which she has left behind. It is by the +population of the chalk sea that the ancient and the modern inhabitants +of the world are most completely connected. The groups which are dying +out flourish, side by side, with the groups which are now the dominant +forms of life. Thus the chalk contains remains of those strange flying +and swimming reptiles, the pterodactyl, the ichthyosaurus, and the +plesiosaurus, which are found in no later deposits, but abounded in +preceding ages. The chambered shells called ammonites and belemnites, +which are so characteristic of the period preceding the cretaceous, in +like manner die with it. + +But, amongst these fading remainders of a previous state of things, are +some very modern forms of life, looking like Yankee pedlars among a tribe +of Red Indians. Crocodiles of modern type appear; bony fishes, many of +them very similar to existing species, almost supplant the forms of fish +which predominate in more ancient seas; and many kinds of living shell- +fish first become known to us in the chalk. The vegetation acquires a +modern aspect. A few living animals are not even distinguishable as +species, from those which existed at that remote epoch. The _Globigerina_ +of the present day, for example, is not different specifically from that +of the chalk; and the same maybe said of many other _Foraminifera_. I +think it probable that critical and unprejudiced examination will show +that more than one species of much higher animals have had a similar +longevity; but the only example which I can at present give confidently +is the snake's-head lampshell (_Terebratulina caput serpentis_), which +lives in our English seas and abounded (as _Terebratulina striata_ of +authors) in the chalk. + +The longest line of human ancestry must hide its diminished head before +the pedigree of this insignificant shell-fish. We Englishmen are proud to +have an ancestor who was present at the Battle of Hastings. The ancestors +of _Terebratulina caput serpentis_ may have been present at a battle of +_Ichthyosauria_ in that part of the sea which, when the chalk was +forming, flowed over the site of Hastings. While all around has changed, +this _Terebratulina_ has peacefully propagated its species from +generation to generation, and stands to this day, as a living testimony +to the continuity of the present with the past history of the globe. + + +Up to this moment I have stated, so far as I know, nothing but well- +authenticated facts, and the immediate conclusions which they force upon +the mind. But the mind is so constituted that it does not willingly rest +in facts and immediate causes, but seeks always after a knowledge of the +remoter links in the chain of causation. + +Taking the many changes of any given spot of the earth's surface, from +sea to land and from land to sea, as an established fact, we cannot +refrain from asking ourselves how these changes have occurred. And when +we have explained them--as they must be explained--by the alternate slow +movements of elevation and depression which have affected the crust of +the earth, we go still further back, and ask, Why these movements? + +I am not certain that any one can give you a satisfactory answer to that +question. Assuredly I cannot. All that can be said, for certain, is, that +such movements are part of the ordinary course of nature, inasmuch as +they are going on at the present time. Direct proof may be given, that +some parts of the land of the northern hemisphere are at this moment +insensibly rising and others insensibly sinking; and there is indirect, +but perfectly satisfactory, proof, that an enormous area now covered by +the Pacific has been deepened thousands of feet, since the present +inhabitants of that sea came into existence. Thus there is not a shadow +of a reason for believing that the physical changes of the globe, in past +times, have been effected by other than natural causes. Is there any more +reason for believing that the concomitant modifications in the forms of +the living inhabitants of the globe have been brought about in other +ways? + +Before attempting to answer this question, let us try to form a distinct +mental picture of what has happened in some special case. The crocodiles +are animals which, as a group, have a very vast antiquity. They abounded +ages before the chalk was deposited; they throng the rivers in warm +climates, at the present day. There is a difference in the form of the +joints of the back-bone, and in some minor particulars, between the +crocodiles of the present epoch and those which lived before the chalk; +but, in the cretaceous epoch, as I have already mentioned, the crocodiles +had assumed the modern type of structure. Notwithstanding this, the +crocodiles of the chalk are not identically the same as those which lived +in the times called "older tertiary," which succeeded the cretaceous +epoch; and the crocodiles of the older tertiaries are not identical with +those of the newer tertiaries, nor are these identical with existing +forms. I leave open the question whether particular species may have +lived on from epoch to epoch. But each epoch has had its peculiar +crocodiles; though all, since the chalk, have belonged to the modern +type, and differ simply in their proportions, and in such structural +particulars as are discernible only to trained eyes. + +How is the existence of this long succession of different species of +crocodiles to be accounted for? Only two suppositions seem to be open to +us--Either each species of crocodile has been specially created, or it +has arisen out of some pre-existing form by the operation of natural +causes. Choose your hypothesis; I have chosen mine. I can find no +warranty for believing in the distinct creation of a score of successive +species of crocodiles in the course of countless ages of time. Science +gives no countenance to such a wild fancy; nor can even the perverse +ingenuity of a commentator pretend to discover this sense, in the simple +words in which the writer of Genesis records the proceedings of the fifth +and six days of the Creation. + +On the other hand, I see no good reason for doubting the necessary +alternative, that all these varied species have been evolved from pre- +existing crocodilian forms, by the operation of causes as completely a +part of the common order of nature as those which have effected the +changes of the inorganic world. Few will venture to affirm that the +reasoning which applies to crocodiles loses its force among other +animals, or among plants. If one series of species has come into +existence by the operation of natural causes, it seems folly to deny that +all may have arisen in the same way. + +A small beginning has led us to a great ending. If I were to put the bit +of chalk with which we started into the hot but obscure flame of burning +hydrogen, it would presently shine like the sun. It seems to me that this +physical metamorphosis is no false image of what has been the result of +our subjecting it to a jet of fervent, though nowise brilliant, thought +to-night. It has become luminous, and its clear rays, penetrating the +abyss of the remote past, have brought within our ken some stages of the +evolution of the earth. And in the shifting "without haste, but without +rest" of the land and sea, as in the endless variation of the forms +assumed by living beings, we have observed nothing but the natural +product of the forces originally possessed by the substance of the +universe. + + + +II + + +THE PROBLEMS OF THE DEEP SEA + +[1873] + +On the 21st of December, 1872, H.M.S. _Challenger_, an eighteen gun +corvette, of 2,000 tons burden, sailed from Portsmouth harbour for a +three, or perhaps four, years' cruise. No man-of-war ever left that +famous port before with so singular an equipment. Two of the eighteen +sixty-eight pounders of the _Challenger's_ armament remained to enable +her to speak with effect to sea-rovers, haply devoid of any respect for +science, in the remote seas for which she is bound; but the main-deck +was, for the most part, stripped of its war-like gear, and fitted up with +physical, chemical, and biological laboratories; Photography had its dark +cabin; while apparatus for dredging, trawling, and sounding; for +photometers and for thermometers, filled the space formerly occupied by +guns and gun-tackle, pistols and cutlasses. + +The crew of the _Challenger_ match her fittings. Captain Nares, his +officers and men, are ready to look after the interests of hydrography, +work the ship, and, if need be, fight her as seamen should; while there +is a staff of scientific civilians, under the general direction of Dr. +Wyville Thomson, F.R.S. (Professor of Natural History in Edinburgh +University by rights, but at present detached for duty _in partibus_), +whose business it is to turn all the wonderfully packed stores of +appliances to account, and to accumulate, before the ship returns to +England, such additions to natural knowledge as shall justify the labour +and cost involved in the fitting out and maintenance of the expedition. + +Under the able and zealous superintendence of the Hydrographer, Admiral +Richards, every precaution which experience and forethought could devise +has been taken to provide the expedition with the material conditions of +success; and it would seem as if nothing short of wreck or pestilence, +both most improbable contingencies, could prevent the _Challenger_ from +doing splendid work, and opening up a new era in the history of +scientific voyages. + +The dispatch of this expedition is the culmination of a series of such +enterprises, gradually increasing in magnitude and importance, which the +Admiralty, greatly to its credit, has carried out for some years past; +and the history of which is given by Dr. Wyville Thomson in the +beautifully illustrated volume entitled "The Depths of the Sea," +published since his departure. + +"In the spring of the year 1868, my friend Dr. W.B. Carpenter, at that +time one of the Vice-Presidents of the Royal Society, was with me in +Ireland, where we were working out together the structure and development +of the Crinoids. I had long previously had a profound conviction that the +land of promise for the naturalist, the only remaining region where there +were endless novelties of extraordinary interest ready to the hand which +had the means of gathering them, was the bottom of the deep sea. I had +even had a glimpse of some of these treasures, for I had seen, the year +before, with Prof. Sars, the forms which I have already mentioned dredged +by his son at a depth of 300 to 400 fathoms off the Loffoten Islands. I +propounded my views to my fellow-labourer, and we discussed the subject +many times over our microscopes. I strongly urged Dr. Carpenter to use +his influence at head-quarters to induce the Admiralty, probably through +the Council of the Royal Society, to give us the use of a vessel properly +fitted with dredging gear and all necessary scientific apparatus, that +many heavy questions as to the state of things in the depths of the +ocean, which were still in a state of uncertainty, might be definitely +settled. After full consideration, Dr. Carpenter promised his hearty co- +operation, and we agreed that I should write to him on his return to +London, indicating generally the results which I anticipated, and +sketching out what I conceived to be a promising line of inquiry. The +Council of the Royal Society warmly supported the proposal; and I give +here in chronological order the short and eminently satisfactory +correspondence which led to the Admiralty placing at the disposal of Dr. +Carpenter and myself the gunboat _Lightninq_, under the command of Staff- +Commander May, R.N., in the summer of 1868, for a trial cruise to the +North of Scotland, and afterwards to the much wider surveys in H.M.S. +_Porcupine_, Captain Calver, R.N., which were made with the additional +association of Mr. Gwyn Jeffreys, in the summers of the years 1869 and +1870."[1] + +[Footnote 1: The Depths of the Sea, pp. 49-50.] + +Plain men may be puzzled to understand why Dr. Wyville Thomson, not being +a cynic, should relegate the "Land of Promise" to the bottom of the deep +sea, they may still more wonder what manner of "milk and honey" the +_Challenger_ expects to find; and their perplexity may well rise to its +maximum, when they seek to divine the manner in which that milk and honey +are to be got out of so inaccessible a Canaan. I will, therefore, +endeavour to give some answer to these questions in an order the reverse +of that in which I have stated them. + +Apart from hooks, and lines, and ordinary nets, fishermen have, from time +immemorial, made use of two kinds of implements for getting at sea- +creatures which live beyond tide-marks--these are the "dredge" and the +"trawl." The dredge is used by oyster-fishermen. Imagine a large bag, the +mouth of which has the shape of an elongated parallelogram, and is +fastened to an iron frame of the same shape, the two long sides of this +rim being fashioned into scrapers. Chains attach the ends of the frame to +a stout rope, so that when the bag is dragged along by the rope the edge +of one of the scrapers rests on the ground, and scrapes whatever it +touches into the bag. The oyster-dredger takes one of these machines in +his boat, and when he has reached the oyster-bed the dredge is tossed +overboard; as soon as it has sunk to the bottom the rope is paid out +sufficiently to prevent it from pulling the dredge directly upwards, and +is then made fast while the boat goes ahead. The dredge is thus dragged +along and scrapes oysters and other sea-animals and plants, stones, and +mud into the bag. When the dredger judges it to be full he hauls it up, +picks out the oysters, throws the rest overboard, and begins again. + +Dredging in shallow water, say ten to twenty fathoms, is an easy +operation enough; but the deeper the dredger goes, the heavier must be +his vessel, and the stouter his tackle, while the operation of hauling up +becomes more and more laborious. Dredging in 150 fathoms is very hard +work, if it has to be carried on by manual labour; but by the use of the +donkey-engine to supply power,[2] and of the contrivances known as +"accumulators," to diminish the risk of snapping the dredge rope by the +rolling and pitching of the vessel, the dredge has been worked deeper and +deeper, until at last, on the 22nd of July, 1869, H.M.S. _Porcupine_ +being in the Bay of Biscay, Captain Calver, her commander, performed the +unprecedented feat of dredging in 2,435 fathoms, or 14,610 feet, a depth +nearly equal to the height of Mont Blanc. The dredge "was rapidly hauled +on deck at one o'clock in the morning of the 23rd, after an absence of +7-1/4 hours, and a journey of upwards of eight statute miles," with a +hundred weight and a half of solid contents. + +[Footnote 2: The emotional side of the scientific nature has its +singularities. Many persons will call to mind a certain philosopher's +tenderness over his watch--"the little creature"--which was so singularly +lost and found again. But Dr. Wyville Thomson surpasses the owner of the +watch in his loving-kindness towards a donkey-engine. "This little engine +was the comfort of our lives. Once or twice it was overstrained, and then +we pitied the willing little thing, panting like an overtaxed horse."] + +The trawl is a sort of net for catching those fish which habitually live +at the bottom of the sea, such as soles, plaice, turbot, and gurnett. The +mouth of the net may be thirty or forty feet wide, and one edge of its +mouth is fastened to a beam of wood of the same length. The two ends of +the beam are supported by curved pieces of iron, which raise the beam and +the edge of the net which is fastened to it, for a short distance, while +the other edge of the mouth of the net trails upon the ground. The closed +end of the net has the form of a great pouch; and, as the beam is dragged +along, the fish, roused from the bottom by the sweeping of the net, +readily pass into its mouth and accumulate in the pouch at its end. After +drifting with the tide for six or seven hours the trawl is hauled up, the +marketable fish are picked out, the others thrown away, and the trawl +sent overboard for another operation. + +More than a thousand sail of well-found trawlers are constantly engaged +in sweeping the seas around our coast in this way, and it is to them that +we owe a very large proportion of our supply of fish. The difficulty of +trawling, like that of dredging, rapidly increases with the depth at +which the operation is performed; and, until the other day, it is +probable that trawling at so great a depth as 100 fathoms was something +unheard of. But the first news from the _Challenger_ opens up new +possibilities for the trawl. + +Dr. Wyville Thomson writes ("Nature," March 20, 1873):-- + +"For the first two or three hauls in very deep water off the coast of +Portugal, the dredge came up filled with the usual 'Atlantic ooze,' +tenacious and uniform throughout, and the work of hours, in sifting, gave +the very smallest possible result. We were extremely anxious to get some +idea of the general character of the Fauna, and particularly of the +distribution of the higher groups; and after various suggestions for +modification of the dredge, it was proposed to try the ordinary trawl. We +had a compact trawl, with a 15-feet beam, on board, and we sent it down +off Cape St. Vincent at a depth of 600 fathoms. The experiment looked +hazardous, but, to our great satisfaction, the trawl came up all right +and contained, with many of the larger invertebrate, several fishes.... +After the first attempt we tried the trawl several times at depths of +1090, 1525, and, finally, 2125 fathoms, and always with success." + +To the coral-fishers of the Mediterranean, who seek the precious red +coral, which grows firmly fixed to rocks at a depth of sixty to eighty +fathoms, both the dredge and the trawl would be useless. They, therefore, +have recourse to a sort of frame, to which are fastened long bundles of +loosely netted hempen cord, and which is lowered by a rope to the depth +at which the hempen cords can sweep over the surface of the rocks and +break off the coral, which is brought up entangled in the cords. A +similar contrivance has arisen out of the necessities of deep-sea +exploration. + +In the course of the dredging of the _Porcupine_, it was frequently found +that, while few objects of interest were brought up within the dredge, +many living creatures came up sticking to the outside of the dredge-bag, +and even to the first few fathoms of the dredge-rope. The mouth of the +dredge doubtless rapidly filled with mud, and thus the things it should +have brought up were shut out. To remedy this inconvenience Captain +Calver devised an arrangement not unlike that employed by the coral- +fishers. He fastened half a dozen swabs, such as are used for drying +decks, to the dredge. A swab is something like what a birch-broom would +be if its twigs were made of long, coarse, hempen yarns. These dragged +along after the dredge over the surface of the mud, and entangled the +creatures living there--multitudes of which, twisted up in the strands of +the swabs, were brought to the surface with the dredge. A further +improvement was made by attaching a long iron bar to the bottom of the +dredge bag, and fastening large bunches of teased-out hemp to the end of +this bar. These "tangles" bring up immense quantities of such animals as +have long arms, or spines, or prominences which readily become caught in +the hemp, but they are very destructive to the fragile organisms which +they imprison; and, now that the trawl can be successfully worked at the +greatest depths, it may be expected to supersede them; at least, wherever +the ground is soft enough to permit of trawling. + +It is obvious that between the dredge, the trawl, and the tangles, there +is little chance for any organism, except such as are able to burrow +rapidly, to remain safely at the bottom of any part of the sea which the +_Challenger_ undertakes to explore. And, for the first time in the +history of scientific exploration, we have a fair chance of learning what +the population of the depths of the sea is like in the most widely +different parts of the world. + +And now arises the next question. The means of exploration being fairly +adequate, what forms of life may be looked for at these vast depths? + +The systematic study of the Distribution of living beings is the most +modern branch of Biological Science, and came into existence long after +Morphology and Physiology had attained a considerable development. This +naturally does not imply that, from the time men began to observe natural +phenomena, they were ignorant of the fact that the animals and plants of +one part of the world are different from those in other regions; or that +those of the hills are different from those of the plains in the same +region; or finally that some marine creatures are found only in the +shallows, while others inhabit the deeps. Nevertheless, it was only after +the discovery of America that the attention of naturalists was powerfully +drawn to the wonderful differences between the animal population of the +central and southern parts of the new world and that of those parts of +the old world which lie under the same parallels of latitude. So far back +as 1667 Abraham Mylius, in his treatise "De Animalium origine et +migratione, populorum," argues that, since there are innumerable species +of animals in America which do not exist elsewhere, they must have been +made and placed there by the Deity: Buffon no less forcibly insists upon +the difference between the Faunae of the old and new world. But the first +attempt to gather facts of this order into a whole, and to coordinate +them into a series of generalizations, or laws of Geographical +Distribution, is not a century old, and is contained in the "Specimen +Zoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens," +published, in 1777, by the learned Brunswick Professor, Eberhard +Zimmermann, who illustrates his work by what he calls a "Tabula +Zoographica," which is the oldest distributional map known to me. + +In regard to matters of fact, Zimmermann's chief aim is to show that +among terrestrial mammals, some occur all over the world, while others +are restricted to particular areas of greater or smaller extent; and that +the abundance of species follows temperature, being greatest in warm and +least in cold climates. But marine animals, he thinks, obey no such law. +The Arctic and Atlantic seas, he says, are as full of fishes and other +animals as those of the tropics. It is, therefore, clear that cold does +not affect the dwellers in the sea as it does land animals, and that this +must be the case follows from the fact that sea water, "propter varias +quas continet bituminis spiritusque particulas," freezes with much more +difficulty than fresh water. On the other hand, the heat of the +Equatorial sun penetrates but a short distance below the surface of the +ocean. Moreover, according to Zimmermann, the incessant disturbance of +the mass of the sea by winds and tides, so mixes up the warm and the cold +that life is evenly diffused and abundant throughout the ocean. + +In 1810, Risso, in his work on the Ichthyology of Nice, laid the +foundation of what has since been termed "bathymetrical" distribution, or +distribution in depth, by showing that regions of the sea bottom of +different depths could be distinguished by the fishes which inhabit them. +There was the _littoral region_ between tide marks with its sand-eels, +pipe fishes, and blennies: the _seaweed region_, extending from low- +water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish; +and the _deep-sea region_, from 450 feet to 1500 feet or more, with +its file-fish, sharks, gurnards, cod, and sword-fish. + +More than twenty years later, M.M. Audouin and Milne Edwards carried out +the principle of distinguishing the Faunae of different zones of depth +much more minutely, in their "Recherches pour servir à l'Histoire +Naturelle du Littoral de la France," published in 1832. + +They divide the area included between highwater-mark and lowwater-mark of +spring tides (which is very extensive, on account of the great rise and +fall of the tide on the Normandy coast about St. Malo, where their +observations were made) into four zones, each characterized by its +peculiar invertebrate inhabitants. Beyond the fourth region they +distinguish a fifth, which is never uncovered, and is inhabited by +oysters, scallops, and large starfishes and other animals. Beyond this +they seem to think that animal life is absent.[3] + +[Footnote 3: "Enfin plus has encore, c'est-à-dire alors loin des côtes, +le fond des eaux ne paraît plus être habité, du moms dans nos mers, par +aucun de ces animaux" (1. c. tom. i. p. 237). The "ces animaux" leaves +the meaning of the authors doubtful.] + +Audouin and Milne Edwards were the first to see the importance of the +bearing of a knowledge of the manner in which marine animals are +distributed in depth, on geology. They suggest that, by this means, it +will be possible to judge whether a fossiliferous stratum was formed upon +the shore of an ancient sea, and even to determine whether it was +deposited in shallower or deeper water on that shore; the association of +shells of animals which live in different zones of depth will prove that +the shells have been transported into the position in which they are +found; while, on the other hand, the absence of shells in a deposit will +not justify the conclusion that the waters in which it was formed were +devoid of animal inhabitants, inasmuch as they might have been only too +deep for habitation. + +The new line of investigation thus opened by the French naturalists was +followed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our own +country, in 1840,[4] and by Oersted, in Denmark, a few years later. The +genius of Forbes, combined with his extensive knowledge of botany, +invertebrate zoology, and geology, enabled him to do more than any of his +compeers, in bringing the importance of distribution in depth into +notice; and his researches in the Aegean Sea, and still more his +remarkable paper "On the Geological Relations of the existing Fauna and +Flora of the British Isles," published in 1846, in the first volume of +the "Memoirs of the Geological Survey of Great Britain," attracted +universal attention. + +[Footnote 4: In the paper in the _Memoirs of the Survey_ cited further +on, Forbes writes:-- + +"In an essay 'On the Association of Mollusca on the British Coasts, +considered with reference to Pleistocene Geology,' printed in [the +_Edinburgh Academic Annual_ for] 1840, I described the mollusca, as +distributed on our shores and seas, in four great zones or regions, +usually denominated 'The Littoral zone,' 'The region of Laminariae,' 'The +region of Coral-lines,' and 'The region of Corals.' An extensive series +of researches, chiefly conducted by the members of the committee +appointed by the British Association to investigate the marine geology of +Britain by means of the dredge, have not invalidated this classification, +and the researches of Professor Lovén, in the Norwegian and Lapland seas, +have borne out their correctness The first two of the regions above +mentioned had been previously noticed by Lamoureux, in his account of the +distribution (vertically) of sea-weeds, by Audouin and Milne Edwards in +their _Observations on the Natural History of the coast of France_, and +by Sars in the preface to his _Beskrivelser og Jagttayelser_."] + +On the coasts of the British Islands, Forbes distinguishes four zones or +regions, the Littoral (between tide marks), the Laminarian (between +lowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), and +the Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms). +But, in the deeper waters of the Aegean Sea, between the shore and a depth +of 300 fathoms, Forbes was able to make out no fewer than eight zones of +life, in the course of which the number and variety of forms gradually +diminished until, beyond 300 fathoms, life disappeared altogether. Hence +it appeared as if descent in the sea had much the same effect on life, as +ascent on land. Recent investigations appear to show that Forbes was +right enough in his classification of the facts of distribution in depth +as they are to be observed in the Aegean; and though, at the time he +wrote, one or two observations were extant which might have warned him +not to generalize too extensively from his Aegean experience, his own +dredging work was so much more extensive and systematic than that of any +other naturalist, that it is not wonderful he should have felt justified +in building upon it. Nevertheless, so far as the limit of the range of +life in depth goes, Forbes' conclusion has been completely negatived, and +the greatest depths yet attained show not even an approach to a "zero of +life":-- + +"During the several cruises of H.M. ships _Lightning_ and _Porcupine_ in +the years 1868, 1869, and 1870," says Dr. Wyville Thomson, "fifty-seven +hauls of the dredge were taken in the Atlantic at depths beyond 500 +fathoms, and sixteen at depths beyond 1,000 fathoms, and, in all cases, +life was abundant. In 1869, we took two casts in depths greater than +2,000 fathoms. In both of these life was abundant; and with the deepest +cast, 2,435 fathoms, off the month of the Bay of Biscay, we took living, +well-marked and characteristic examples of all the five invertebrate sub- +kingdoms. And thus the question of the existence of abundant animal life +at the bottom of the sea has been finally settled and for all depths, for +there is no reason to suppose that the depth anywhere exceeds between +three and four thousand fathoms; and if there be nothing in the +conditions of a depth of 2,500 fathoms to prevent the full development of +a varied Fauna, it is impossible to suppose that even an additional +thousand fathoms would make any great difference."[5] + +[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind, +obtained by previous observers, are stated at length in the sixth +chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under +the authority of Professor Peirce, the Superintendent of the United +States Coast Survey, in the years 1867, 1868, and 1869, are particularly +noteworthy, and it is probably not too much to say, in the words of +Professor Agassiz, "that we owe to the coast survey the first broad and +comprehensive basis for an exploration of the sea bottom on a large +scale, opening a new era in zoological and geological research."] + +As Dr. Wyville Thomson's recent letter, cited above, shows, the use of +the trawl, at great depths, has brought to light a still greater +diversity of life. Fishes came up from a depth of 600 to more than 1,000 +fathoms, all in a peculiar condition from the expansion of the air +contained in their bodies. On their relief from the extreme pressure, +their eyes, especially, had a singular appearance, protruding like great +globes from their heads. Bivalve and univalve mollusca seem to be rare at +the greatest depths; but starfishes, sea urchins and other echinoderms, +zoophytes, sponges, and protozoa abound. + +It is obvious that the _Challenger_ has the privilege of opening a new +chapter in the history of the living world. She cannot send down her +dredges and her trawls into these virgin depths of the great ocean +without bringing up a discovery. Even though the thing itself may be +neither "rich nor rare," the fact that it came from that depth, in that +particular latitude and longitude, will be a new fact in distribution, +and, as such, have a certain importance. + +But it may be confidently assumed that the things brought up will very +frequently be zoological novelties; or, better still, zoological +antiquities, which, in the tranquil and little-changed depths of the +ocean, have escaped the causes of destruction at work in the shallows, +and represent the predominant population of a past age. + +It has been seen that Audouin and Milne Edwards foresaw the general +influence of the study of distribution in depth upon the interpretation +of geological phenomena. Forbes connected the two orders of inquiry still +more closely; and in the thoughtful essay "On the connection between the +distribution of the existing Fauna and Flora of the British Isles, and +the geological changes which have affected their area, especially during +the epoch of the Northern drift," to which reference has already been +made, he put forth a most pregnant suggestion. + +In certain parts of the sea bottom in the immediate vicinity of the +British Islands, as in the Clyde district, among the Hebrides, in the +Moray Firth, and in the German Ocean, there are depressed areas, forming a +kind of submarine valleys, the centres of which are from 80 to 100 +fathoms, or more, deep. These depressions are inhabited by assemblages of +marine animals, which differ from those found over the adjacent and +shallower region, and resemble those which are met with much farther +north, on the Norwegian coast. Forbes called these Scandinavian +detachments "Northern outliers." + +How did these isolated patches of a northern population get into these +deep places? To explain the mystery, Forbes called to mind the fact that, +in the epoch which immediately preceded the present, the climate was much +colder (whence the name of "glacial epoch" applied to it); and that the +shells which are found fossil, or sub-fossil, in deposits of that age are +precisely such as are now to be met with only in the Scandinavian, or +still more Arctic, regions. Undoubtedly, during the glacial epoch, the +general population of our seas had, universally, the northern aspect +which is now presented only by the "northern outliers"; just as the +vegetation of the land, down to the sea-level, had the northern character +which is, at present, exhibited only by the plants which live on the tops +of our mountains. But, as the glacial epoch passed away, and the present +climatal conditions were developed, the northern plants were able to +maintain themselves only on the bleak heights, on which southern forms +could not compete with them. And, in like manner, Forbes suggested that, +after the glacial epoch, the northern animals then inhabiting the sea +became restricted to the deeps in which they could hold their own against +invaders from the south, better fitted than they to flourish in the +warmer waters of the shallows. Thus depth in the sea corresponded in its +effect upon distribution to height on the land. + +The same idea is applied to the explanation of a similar anomaly in the +Fauna of the Aegean:-- + +"In the deepest of the regions of depth of the Aegean, the representation +of a Northern Fauna is maintained, partly by identical and partly by +representative forms.... The presence of the latter is essentially due to +the law (of representation of parallels of latitude by zones of depth), +whilst that of the former species depended on their transmission from +their parent seas during a former epoch, and subsequent isolation. That +epoch was doubtless the newer Pliocene or Glacial Era, when the _Mya +truncata_ and other northern forms now extinct in the Mediterranean, and +found fossil in the Sicilian tertiaries, ranged into that sea. The +changes which there destroyed the _shallow water_ glacial forms, did not +affect those living in the depths, and which still survive."[6] + +[Footnote 6: _Memoirs of the Geological Survey of Great Britain_, Vol. i. +p. 390.] + +The conception that the inhabitants of local depressions of the sea +bottom might be a remnant of the ancient population of the area, which +had held their own in these deep fastnesses against an invading Fauna, as +Britons and Gaels have held out in Wales and in Scotland against +encroaching Teutons, thus broached by Forbes, received a wider +application than Forbes had dreamed of when the sounding machine first +brought up specimens of the mud of the deep sea. As I have pointed out +elsewhere,[7] it at once became obvious that the calcareous sticky mud of +the Atlantic was made up, in the main, of shells of _Globigerina_ and +other _Foraminifera_, identical with those of which the true chalk is +composed, and the identity extended even to the presence of those +singular bodies, the Coccoliths and Coccospheres, the true nature of +which is not yet made out. Here then were organisms, as old as the +cretaceous epoch, still alive, and doing their work of rock-making at the +bottom of existing seas. What if _Globigerina_ and the Coccoliths should +not be the only survivors of a world passed away, which are hidden +beneath three miles of salt water? The letter which Dr. Wyville Thomson +wrote to Dr. Carpenter in May, 1868, out of which all these expeditions +have grown, shows that this query had become a practical problem in Dr. +Thomson's mind at that time; and the desirableness of solving the problem +is put in the foreground of his reasons for urging the Government to +undertake the work of exploration:-- + +[Footnote 7: See above, "On a Piece of Chalk," p. 13.] + +"Two years ago, M. Sars, Swedish Government Inspector of Fisheries, had +an opportunity, in his official capacity, of dredging off the Loffoten +Islands at a depth of 300 fathoms. I visited Norway shortly after his +return, and had an opportunity of studying with his father, Professor +Sars, some of his results. Animal forms were _abundant_; many of them +were new to science; and among them was one of surpassing interest, the +small crinoid, of which you have a specimen, and which we at once +recognised as a degraded type of the _Apiocrinidoe_, an order hitherto +regarded as extinct, which attained its maximum in the Pear Encrinites of +the Jurassic period, and whose latest representative hitherto known was +the _Bourguettocrinus_ of the chalk. Some years previously, Mr. +Absjornsen, dredging in 200 fathoms in the Hardangerfjord, procured +several examples of a Starfish (_Brisinga_), which seems to find its +nearest ally in the fossil genus _Protaster_. These observations place it +beyond a doubt that animal life is abundant in the ocean at depths +varying from 200 to 300 fathoms, that the forms at these great depths +differ greatly from those met with in ordinary dredgings, and that, at +all events in some cases, these animals are closely allied to, and would +seem to be directly descended from, the Fauna of the early tertiaries. + +"I think the latter result might almost have been anticipated; and, +probably, further investigation will largely add to this class of data, +and will give us an opportunity of testing our determinations of the +zoological position of some fossil types by an examination of the soft +parts of their recent representatives. The main cause of the destruction, +the migration, and the extreme modification of animal types, appear to be +change of climate, chiefly depending upon oscillations of the earth's +crust. These oscillations do not appear to have ranged, in the Northern +portion of the Northern Hemisphere, much beyond 1,000 feet since the +commencement of the Tertiary Epoch. The temperature of deep waters seems +to be constant for all latitudes at 39°; so that an immense area of the +North Atlantic must have had its conditions unaffected by tertiary or +post-tertiary oscillations."[8] + +[Footnote 8: The Depths of the Sea, pp. 51-52.] + +As we shall see, the assumption that the temperature of the deep sea is +everywhere 39° F. (4° Cent.) is an error, which Dr. Wyville Thomson +adopted from eminent physical writers; but the general justice of the +reasoning is not affected by this circumstance, and Dr. Thomson's +expectation has been, to some extent, already verified. + +Thus besides _Globigerina_, there are eighteen species of deep-sea +_Foraminifera_ identical with species found in the chalk. Imbedded in the +chalky mud of the deep sea, in many localities, are innumerable cup- +shaped sponges, provided with six-rayed silicious spicula, so disposed +that the wall of the cup is formed of a lacework of flinty thread. Not +less abundant, in some parts of the chalk formation, are the fossils +known as _Ventriculites_, well described by Dr. Thomson as "elegant vases +or cups, with branching root-like bases, or groups of regularly or +irregularly spreading tubes delicately fretted on the surface with an +impressed network like the finest lace"; and he adds, "When we compare +such recent forms as _Aphrocallistes, Iphiteon, Holtenia_, and +_Askonema_, with certain series of the chalk _Ventriculites_, there +cannot be the slightest doubt that they belong to the same family--in +some cases to very nearly allied genera."[9] + +[Footnote 9: _The Depths of the Sea_, p. 484.] + +Professor Duncan finds "several corals from the coast of Portugal more +nearly allied to chalk forms than to any others." + +The Stalked Crinoids or Feather Stars, so abundant in ancient times, are +now exclusively confined to the deep sea, and the late explorations have +yielded forms of old affinity, the existence of which has hitherto been +unsuspected. The general character of the group of star fishes imbedded +in the white chalk is almost the same as in the modern Fauna of the deep +Atlantic. The sea urchins of the deep sea, while none of them are +specifically identical with any chalk form, belong to the same general +groups, and some closely approach extinct cretaceous genera. + +Taking these facts in conjunction with the positive evidence of the +existence, during the Cretaceous epoch, of a deep ocean where now lies +the dry land of central and southern Europe, northern Africa, and western +and southern Asia; and of the gradual diminution of this ocean during the +older tertiary epoch, until it is represented at the present day by such +teacupfuls as the Caspian, the Black Sea, and the Mediterranean; the +supposition of Dr. Thomson and Dr. Carpenter that what is now the deep +Atlantic, was the deep Atlantic (though merged in a vast easterly +extension) in the Cretaceous epoch, and that the _Globigerina_ mud has +been accumulating there from that time to this, seems to me to have a +great degree of probability. And I agree with Dr. Wyville Thomson against +Sir Charles Lyell (it takes two of us to have any chance against his +authority) in demurring to the assertion that "to talk of chalk having +been uninterruptedly formed in the Atlantic is as inadmissible in a +geographical as in a geological sense." + +If the word "chalk" is to be used as a stratigraphical term and +restricted to _Globigerina_ mud deposited during the Cretaceous epoch, of +course it is improper to call the precisely similar mud of more recent +date, chalk. If, on the other hand, it is to be used as a mineralogical +term, I do not see how the modern and the ancient chalks are to be +separated--and, looking at the matter geographically, I see no reason to +doubt that a boring rod driven from the surface of the mud which forms +the floor of the mid-Atlantic would pass through one continuous mass of +_Globigerina_ mud, first of modern, then of tertiary, and then of +mesozoic date; the "chalks" of different depths and ages being +distinguished merely by the different forms of other organisms associated +with the _Globigerinoe_. + +On the other hand, I think it must be admitted that a belief in the +continuity of the modern with the ancient chalk has nothing to do with +the proposition that we can, in any sense whatever, be said to be still +living in the Cretaceous epoch. When the _Challenger's_ trawl brings up +an _Ichthyosaurus_, along with a few living specimens of _Belemnites_ and +_Turrilites_, it may be admitted that she has come upon a cretaceous +"outlier." A geological period is characterized not only by the presence +of those creatures which lived in it, but by the absence of those which +have only come into existence later; and, however large a proportion of +true cretaceous forms may be discovered in the deep sea, the modern types +associated with them must be abolished before the Fauna, as a whole, +could, with any propriety, be termed Cretaceous. + + +I have now indicated some of the chief lines of Biological inquiry, in +which the _Challenger_ has special opportunities for doing good service, +and in following which she will be carrying out the work already +commenced by the _Lightning_ and _Porcupine_ in their cruises of 1868 and +subsequent years. + +But biology, in the long run, rests upon physics, and the first condition +for arriving at a sound theory of distribution in the deep sea, is the +precise ascertainment of the conditions of life; or, in other words, a +full knowledge of all those phenomena which are embraced under the head +of the Physical Geography of the Ocean. + +Excellent work has already been done in this direction, chiefly under the +superintendence of Dr. Carpenter, by the _Lightning_ and the +_Porcupine_,[10] and some data of fundamental importance to the physical +geography of the sea have been fixed beyond a doubt. + +[Footnote 10: _Proceedings of the Royal Society_, 1870 and 1872] + +Thus, though it is true that sea-water steadily contracts as it cools +down to its freezing point, instead of expanding before it reaches its +freezing point as fresh water does, the truth has been steadily ignored +by even the highest authorities in physical geography, and the erroneous +conclusions deduced from their erroneous premises have been widely +accepted as if they were ascertained facts. Of course, if sea-water, like +fresh water, were heaviest at a temperature of 39° F. and got lighter as +it approached 32° F., the water of the bottom of the deep sea could not +be colder than 39°. But one of the first results of the careful +ascertainment of the temperature at different depths, by means of +thermometers specially contrived for the avoidance of the errors produced +by pressure, was the proof that, below 1000 fathoms in the Atlantic, down +to the greatest depths yet sounded, the water has a temperature always +lower than 38° Fahr., whatever be the temperature of the water at the +surface. And that this low temperature of the deepest water is probably +the universal rule for the depths of the open ocean is shown, among +others, by Captain Chimmo's recent observations in the Indian ocean, +between Ceylon and Sumatra, where, the surface water ranging from 85°-81° +Fahr., the temperature at the bottom, at a depth of 2270 to 2656 fathoms, +was only from 34° to 32° Fahr. + +As the mean temperature of the superficial layer of the crust of the +earth may be taken at about 50° Fahr., it follows that the bottom layer +of the deep sea in temperate and hot latitudes, is, on the average, much +colder than either of the bodies with which it is in contact; for the +temperature of the earth is constant, while that of the air rarely falls +so low as that of the bottom water in the latitudes in question; and even +when it does, has time to affect only a comparatively thin stratum of the +surface water before the return of warm weather. + +How does this apparently anomalous state of things come about? If we +suppose the globe to be covered with a universal ocean, it can hardly be +doubted that the cold of the regions towards the poles must tend to cause +the superficial water of those regions to contract and become +specifically heavier. Under these circumstances, it would have no +alternative but to descend and spread over the sea bottom, while its +place would be taken by warmer water drawn from the adjacent regions. +Thus, deep, cold, polar-equatorial currents, and superficial, warmer, +equatorial-polar currents, would be set up; and as the former would have +a less velocity of rotation from west to east than the regions towards +which they travel, they would not be due southerly or northerly currents, +but south-westerly in the northern hemisphere, and north-westerly in the +southern; while, by a parity of reasoning, the equatorial-polar warm +currents would be north-easterly in the northern hemisphere, and south- +easterly in the southern. Hence, as a north-easterly current has the same +direction as a south-westerly wind, the direction of the northern +equatorial-polar current in the extra-tropical part of its course would +pretty nearly coincide with that of the anti-trade winds. The freezing of +the surface of the polar sea would not interfere with the movement thus +set up. For, however bad a conductor of heat ice may be, the unfrozen +sea-water immediately in contact with the undersurface of the ice must +needs be colder than that further off; and hence will constantly tend to +descend through the subjacent warmer water. + +In this way, it would seem inevitable that the surface waters of the +northern and southern frigid zones must, sooner or later, find their way +to the bottom of the rest of the ocean; and there accumulate to a +thickness dependent on the rate at which they absorb heat from the crust +of the earth below, and from the surface water above. + +If this hypothesis be correct, it follows that, if any part of the ocean +in warm latitudes is shut off from the influence of the cold polar +underflow, the temperature of its deeps should be less cold than the +temperature of corresponding depths in the open sea. Now, in the +Mediterranean, Nature offers a remarkable experimental proof of just the +kind needed. It is a landlocked sea which runs nearly east and west, +between the twenty-ninth and forty-fifth parallels of north latitude. +Roughly speaking, the average temperature of the air over it is 75° Fahr. +in July and 48° in January. + +This great expanse of water is divided by the peninsula of Italy +(including Sicily), continuous with which is a submarine elevation +carrying less than 1,200 feet of water, which extends from Sicily to Cape +Bon in Africa, into two great pools--an eastern and a western. The +eastern pool rapidly deepens to more than 12,000 feet, and sends off to +the north its comparatively shallow branches, the Adriatic and the Aegean +Seas. The western pool is less deep, though it reaches some 10,000 feet. +And, just as the western end of the eastern pool communicates by a +shallow passage, not a sixth of its greatest depth, with the western +pool, so the western pool is separated from the Atlantic by a ridge which +runs between Capes Trafalgar and Spartel, on which there is hardly 1,000 +feet of water. All the water of the Mediterranean which lies deeper than +about 150 fathoms, therefore, is shut off from that of the Atlantic, and +there is no communication between the cold layer of the Atlantic (below +1,000 fathoms) and the Mediterranean. Under these circumstances, what is +the temperature of the Mediterranean? Everywhere below 600 feet it is +about 55° Fahr.; and consequently, at its greatest depths, it is some 20° +warmer than the corresponding depths of the Atlantic. + +It seems extremely difficult to account for this difference in any other +way, than by adopting the views so strongly and ably advocated by Dr. +Carpenter, that, in the existing distribution of land and water, such a +circulation of the water of the ocean does actually occur, as +theoretically must occur, in the universal ocean, with which we started. + +It is quite another question, however, whether this theoretic +circulation, true cause as it may be, is competent to give rise to such +movements of sea-water, in mass, as those currents, which have commonly +been regarded as northern extensions of the Gulf-stream. I shall not +venture to touch upon this complicated problem; but I may take occasion +to remark that the cause of a much simpler phenomenon--the stream of +Atlantic water which sets through the Straits of Gibraltar, eastward, at +the rate of two or three miles an hour or more, does not seem to be so +clearly made out as is desirable. + +The facts appear to be that the water of the Mediterranean is very +slightly denser than that of the Atlantic (1.0278 to 1.0265), and that +the deep water of the Mediterranean is slightly denser than that of the +surface; while the deep water of the Atlantic is, if anything, lighter +than that of the surface. Moreover, while a rapid superficial current is +setting in (always, save in exceptionally violent easterly winds) through +the Straits of Gibraltar, from the Atlantic to the Mediterranean, a deep +undercurrent (together with variable side currents) is setting out +through the Straits, from the Mediterranean to the Atlantic. + +Dr. Carpenter adopts, without hesitation, the view that the cause of this +indraught of Atlantic water is to be sought in the much more rapid +evaporation which takes place from the surface of the Mediterranean than +from that of the Atlantic; and thus, by lowering the level of the former, +gives rise to an indraught from the latter. + +But is there any sound foundation for the three assumptions involved +here? Firstly, that the evaporation from the Mediterranean, as a whole, +is much greater than that from the Atlantic under corresponding +parallels; secondly, that the rainfall over the Mediterranean makes up +for evaporation less than it does over the Atlantic; and thirdly, +supposing these two questions answered affirmatively: Are not these +sources of loss in the Mediterranean fully covered by the prodigious +quantity of fresh water which is poured into it by great rivers and +submarine springs? Consider that the water of the Ebro, the Rhine, the +Po, the Danube, the Don, the Dnieper, and the Nile, all flow directly or +indirectly into the Mediterranean; that the volume of fresh water which +they pour into it is so enormous that fresh water may sometimes be baled +up from the surface of the sea off the Delta of the Nile, while the land +is not yet in sight; that the water of the Black Sea is half fresh, and +that a current of three or four miles an hour constantly streams from it +Mediterraneanwards through the Bosphorus;--consider, in addition, that no +fewer than ten submarine springs of fresh water are known to burst up in +the Mediterranean, some of them so large that Admiral Smyth calls them +"subterranean rivers of amazing volume and force"; and it would seem, on +the face of the matter, that the sun must have enough to do to keep the +level of the Mediterranean down; and that, possibly, we may have to seek +for the cause of the small superiority in saline contents of the +Mediterranean water in some condition other than solar evaporation. + +Again, if the Gibraltar indraught is the effect of evaporation, why does +it go on in winter as well as in summer? + +All these are questions more easily asked than answered; but they must be +answered before we can accept the Gibraltar stream as an example of a +current produced by indraught with any comfort. + +The Mediterranean is not included in the _Challenger's_ route, but she +will visit one of the most promising and little explored of +hydrographical regions--the North Pacific, between Polynesia and the +Asiatic and American shores; and doubtless the store of observations upon +the currents of this region, which she will accumulate, when compared +with what we know of the North Atlantic, will throw a powerful light upon +the present obscurity of the Gulf-stream problem. + + + +III + + +ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. _CHALLLENGER_ + +[1875] + +In May, 1873, I drew attention[1] to the important problems connected +with the physics and natural history of the sea, to the solution of which +there was every reason to hope the cruise of H.M.S. _Challenger_ would +furnish important contributions. The expectation then expressed has not +been disappointed. Reports to the Admiralty, papers communicated to the +Royal Society, and large collections which have already been sent home, +have shown that the _Challenger's_ staff have made admirable use of their +great opportunities; and that, on the return of the expedition in 1874, +their performance will be fully up to the level of their promise. Indeed, +I am disposed to go so far as to say, that if nothing more came of the +_Challengers_ expedition than has hitherto been yielded by her +exploration of the nature of the sea bottom at great depths, a full +scientific equivalent of the trouble and expense of her equipment would +have been obtained. + +[Footnote 1: See the preceding Essay.] + +In order to justify this assertion, and yet, at the same time, not to +claim more for Professor Wyville Thomson and his colleagues than is their +due, I must give a brief history of the observations which have preceded +their exploration of this recondite field of research, and endeavour to +make clear what was the state of knowledge in December, 1872, and what +new facts have been added by the scientific staff of the _Challenger_. So +far as I have been able to discover, the first successful attempt to +bring up from great depths more of the sea bottom than would adhere to a +sounding-lead, was made by Sir John Ross, in the voyage to the Arctic +regions which he undertook in 1818. In the Appendix to the narrative of +that voyage, there will be found an account of a very ingenious apparatus +called "clams"--a sort of double scoop--of his own contrivance, which Sir +John Ross had made by the ship's armourer; and by which, being in +Baffin's Bay, in 72° 30' N. and 77° 15' W., he succeeded in bringing up +from 1,050 fathoms (or 6,300 feet), "several pounds" of a "fine green +mud," which formed the bottom of the sea in this region. Captain (now Sir +Edward) Sabine, who accompanied Sir John Ross on this cruise, says of +this mud that it was "soft and greenish, and that the lead sunk several +feet into it." A similar "fine green mud" was found to compose the sea +bottom in Davis Straits by Goodsir in 1845. Nothing is certainly known of +the exact nature of the mud thus obtained, but we shall see that the mud +of the bottom of the Antarctic seas is described in curiously similar +terms by Dr. Hooker, and there is no doubt as to the composition of this +deposit. + +In 1850, Captain Penny collected in Assistance Bay, in Kingston Bay, and +in Melville Bay, which lie between 73° 45' and 74° 40' N., specimens of +the residuum left by melted surface ice, and of the sea bottom in these +localities. Dr. Dickie, of Aberdeen, sent these materials to Ehrenberg, +who made out[2] that the residuum of the melted ice consisted for the +most part of the silicious cases of diatomaceous plants, and of the +silicious spicula of sponges; while, mixed with these, were a certain +number of the equally silicious skeletons of those low animal organisms, +which were termed _Polycistineoe_ by Ehrenberg, but are now known as +_Radiolaria_. + +[Footnote 2: _Ueber neue Anschauungen des kleinsten nördlichen +Polarlebens_.--Monatsberichte d. K. Akad. Berlin, 1853.] + +In 1856, a very remarkable addition to our knowledge of the nature of the +sea bottom in high northern latitudes was made by Professor Bailey of +West Point. Lieutenant Brooke, of the United States Navy, who was +employed in surveying the Sea of Kamschatka, had succeeded in obtaining +specimens of the sea bottom from greater depths than any hitherto +reached, namely from 2,700 fathoms (16,200 feet) in 56° 46' N., and 168° +18' E.; and from 1,700 fathoms (10,200 feet) in 60° 15' N. and 170° 53' +E. On examining these microscopically, Professor Bailey found, as +Ehrenberg had done in the case of mud obtained on the opposite side of +the Arctic region, that the fine mud was made up of shells of +_Diatomacoe_, of spicula of sponges, and of _Radiolaria_, with a small +admixture of mineral matters, but without a trace of any calcareous +organisms. + +Still more complete information has been obtained concerning the nature +of the sea bottom in the cold zone around the south pole. Between the +years 1839 and 1843, Sir James Clark Ross executed his famous Antarctic +expedition, in the course of which he penetrated, at two widely distant +points of the Antarctic zone, into the high latitudes of the shores of +Victoria Land and of Graham's Land, and reached the parallel of 80° S. +Sir James Ross was himself a naturalist of no mean acquirements, and Dr. +Hooker,[3] the present President of the Royal Society, accompanied him as +naturalist to the expedition, so that the observations upon the fauna and +flora of the Antarctic regions made during this cruise were sure to have +a peculiar value and importance, even had not the attention of the +voyagers been particularly directed to the importance of noting the +occurrence of the minutest forms of animal and vegetable life in the +ocean. + +[Footnote 3: Now Sir Joseph Hooker. 1894.] + +Among the scientific instructions for the voyage drawn up by a committee +of the Royal Society, however, there is a remarkable letter from Von +Humboldt to Lord Minto, then First Lord of the Admiralty, in which, among +other things, he dwells upon the significance of the researches into the +microscopic composition of rocks, and the discovery of the great share +which microscopic organisms take in the formation of the crust of the +earth at the present day, made by Ehrenberg in the years 1836-39. +Ehrenberg, in fact, had shown that the extensive beds of "rotten-stone" +or "Tripoli" which occur in various parts of the world, and notably at +Bilin in Bohemia, consisted of accumulations of the silicious cases and +skeletons of _Diatomaceoe_, sponges, and _Radiolaria_; he had proved that +similar deposits were being formed by _Diatomaceoe_, in the pools of the +Thiergarten in Berlin and elsewhere, and had pointed out that, if it were +commercially worth while, rotten-stone might be manufactured by a process +of diatom-culture. Observations conducted at Cuxhaven in 1839, had +revealed the existence, at the surface of the waters of the Baltic, of +living Diatoms and _Radiolaria_ of the same species as those which, in a +fossil state, constitute extensive rocks of tertiary age at Caltanisetta, +Zante, and Oran, on the shores of the Mediterranean. + +Moreover, in the fresh-water rotten-stone beds of Bilin, Ehrenberg had +traced out the metamorphosis, effected apparently by the action of +percolating water, of the primitively loose and friable deposit of +organized particles, in which the silex exists in the hydrated or soluble +condition. The silex, in fact, undergoes solution and slow redeposition, +until, in ultimate result, the excessively fine-grained sand, each +particle of which is a skeleton, becomes converted into a dense opaline +stone, with only here and there an indication of an organism. + +From the consideration of these facts, Ehrenberg, as early as the year +1839, had arrived at the conclusion that rocks, altogether similar to +those which constitute a large part of the crust of the earth, must be +forming, at the present day, at the bottom of the sea; and he threw out +the suggestion that even where no trace of organic structure is to be +found in the older rocks, it may have been lost by metamorphosis.[4] + +[Footnote 4: _Ueber die noch jetzt zahlreich lebende Thierarten der +Kreidebildung und den Organismus der Polythalamien. Abhandlungen der Kön. +Akad. der Wissenchaften._ 1839. _Berlin_. 1841. I am afraid that this +remarkable paper has been somewhat overlooked in the recent discussions +of the relation of ancient rocks to modern deposits.] + +The results of the Antarctic exploration, as stated by Dr. Hooker in the +"Botany of the Antarctic Voyage," and in a paper which he read before +the British Association in 1847, are of the greatest importance in +connection with these views, and they are so clearly stated in the former +work, which is somewhat inaccessible, that I make no apology for quoting +them at length-- + +"The waters and the ice of the South Polar Ocean were alike found to +abound with microscopic vegetables belonging to the order _Diatomaceoe_. +Though much too small to be discernible by the naked eye, they occurred +in such countless myriads as to stain the berg and the pack ice wherever +they were washed by the swell of the sea; and, when enclosed in the +congealing surface of the water, they imparted to the brash and pancake +ice a pale ochreous colour. In the open ocean, northward of the frozen +zone, this order, though no doubt almost universally present, generally +eludes the search of the naturalist; except when its species are +congregated amongst that mucous scum which is sometimes seen floating on +the waves, and of whose real nature we are ignorant; or when the coloured +contents of the marine animals who feed on these Algae are examined. To +the south, however, of the belt of ice which encircles the globe, between +the parallels of 50° and 70° S., and in the waters comprised between that +belt and the highest latitude ever attained by man, this vegetation is +very conspicuous, from the contrast between its colour and the white snow +and ice in which it is imbedded. Insomuch, that in the eightieth degree, +all the surface ice carried along by the currents, the sides of every +berg and the base of the great Victoria Barrier itself, within reach of +the swell, were tinged brown, as if the polar waters were charged with +oxide of iron. + +"As the majority of these plants consist of very simple vegetable cells, +enclosed in indestructible silex (as other Algae are in carbonate of +lime), it is obvious that the death and decomposition of such multitudes +must form sedimentary deposits, proportionate in their extent to the +length and exposure of the coast against which they are washed, in +thickness to the power of such agents as the winds, currents, and sea, +which sweep them more energetically to certain positions, and in purity, +to the depth of the water and nature of the bottom. Hence we detected +their remains along every icebound shore, in the depths of the adjacent +ocean, between 80 and 400 fathoms. Off Victoria Barrier (a perpendicular +wall of ice between one and two hundred feet above the level of the sea) +the bottom of the ocean was covered with a stratum of pure white or green +mud, composed principally of the silicious shells of the _Diatomaceoe_. +These, on being put into water, rendered it cloudy like milk, and took +many hours to subside. In the very deep water off Victoria and Graham's +Land, this mud was particularly pure and fine; but towards the shallow +shores there existed a greater or less admixture of disintegrated rock +and sand; so that the organic compounds of the bottom frequently bore but +a small proportion to the inorganic." ... + +"The universal existence of such an invisible vegetation as that of the +Antarctic Ocean, is a truly wonderful fact, and the more from its not +being accompanied by plants of a high order. During the years we spent +there, I had been accustomed to regard the phenomena of life as differing +totally from what obtains throughout all other latitudes, for everything +living appeared to be of animal origin. The ocean swarmed with +_Mollusca_, and particularly entomostracous _Crustacea_, small whales, +and porpoises; the sea abounded with penguins and seals, and the air with +birds; the animal kingdom was ever present, the larger creatures preying +on the smaller, and these again on smaller still; all seemed carnivorous. +The herbivorous were not recognised, because feeding on a microscopic +herbage, of whose true nature I had formed an erroneous impression. It +is, therefore, with no little satisfaction that I now class the +_Diatomaceoe_ with plants, probably maintaining in the South Polar Ocean +that balance between the vegetable and the animal kingdoms which prevails +over the surface of our globe. Nor is the sustenance and nutrition of the +animal kingdom the only function these minute productions may perform; +they may also be the purifiers of the vitiated atmosphere, and thus +execute in the Antarctic latitudes the office of our trees and grass turf +in the temperate regions, and the broad leaves of the palm, &c., in the +tropics." ... + +With respect to the distribution of the _Diatomaceoe_, Dr. Hooker +remarks:-- + +"There is probably no latitude between that of Spitzbergen and Victoria +Land, where some of the species of either country do not exist: Iceland, +Britain, the Mediterranean Sea, North and South America, and the South +Sea Islands, all possess Antarctic _Diatomaceoe_. The silicious coats of +species only known living in the waters of the South Polar Ocean, have, +during past ages, contributed to the formation of rocks; and thus they +outlive several successive creations of organized beings. The phonolite +stones of the Rhine, and the Tripoli stone, contain species identical +with what are now contributing to form a sedimentary deposit (and +perhaps, at some future period, a bed of rock) extending in one +continuous stratum for 400 measured miles. I allude to the shores of the +Victoria Barrier, along whose coast the soundings examined were +invariably charged with diatomaceous remains, constituting a bank which +stretches 200 miles north from the base of Victoria Barrier, while the +average depth of water above it is 300 fathoms, or 1,800 feet. Again, +some of the Antarctic species have been detected floating in the +atmosphere which overhangs the wide ocean between Africa and America. The +knowledge of this marvellous fact we owe to Mr. Darwin, who, when he was +at sea off the Cape de Verd Islands, collected an impalpable powder which +fell on Captain Fitzroy's ship. He transmitted this dust to Ehrenberg, +who ascertained it to consist of the silicious coats, chiefly of American +_Diatomaceoe_, which were being wafted through the upper region of the +air, when some meteorological phenomena checked them in their course and +deposited them on the ship and surface of the ocean. + +"The existence of the remains of many species of this order (and amongst +them some Antarctic ones) in the volcanic ashes, pumice, and scoriae of +active and extinct volcanoes (those of the Mediterranean Sea and +Ascension Island, for instance) is a fact bearing immediately upon the +present subject. Mount Erebus, a volcano 12,400 feet high, of the first +class in dimensions and energetic action, rises at once from the ocean in +the seventy-eighth degree of south latitude, and abreast of the +_Diatomaceoe_ bank, which reposes in part on its base. Hence it may not +appear preposterous to conclude that, as Vesuvius receives the waters of +the Mediterranean, with its fish, to eject them by its crater, so the +subterranean and subaqueous forces which maintain Mount Erebus in +activity may occasionally receive organic matter from the bank, and +disgorge it, together with those volcanic products, ashes and pumice. + +"Along the shores of Graham's Land and the South Shetland Islands, we +have a parallel combination of igneous and aqueous action, accompanied +with an equally copious supply of _Diatomaceoe_. In the Gulf of Erebus +and Terror, fifteen degrees north of Victoria Land, and placed on the +opposite side of the globe, the soundings were of a similar nature with +those of the Victoria Land and Barrier, and the sea and ice as full of +_Diatomaceoe_. This was not only proved by the deep sea lead, but by the +examination of bergs which, once stranded, had floated off and become +reversed, exposing an accumulation of white friable mud frozen to their +bases, which abounded with these vegetable remains." + +The _Challenger_ has explored the Antarctic seas in a region intermediate +between those examined by Sir James Ross's expedition; and the +observations made by Dr. Wyville Thomson and his colleagues in every +respect confirm those of Dr. Hooker:-- + +"On the 11th of February, lat. 60° 52' S., long. 80° 20' E., and March 3, +lat. 53° 55' S., long. 108° 35' E., the sounding instrument came up +filled with a very fine cream-coloured paste, which scarcely effervesced +with acid, and dried into a very light, impalpable, white powder. This, +when examined under the microscope, was found to consist almost entirely +of the frustules of Diatoms, some of them wonderfully perfect in all the +details of their ornament, and many of them broken up. The species of +Diatoms entering into this deposit have not yet been worked up, but they +appear to be referable chiefly to the genera _Fragillaria, Coscinodiscus, +Choetoceros, Asteromphalus_, and _Dictyocha_, with fragments of the +separated rods of a singular silicious organism, with which we were +unacquainted, and which made up a large proportion of the finer matter of +this deposit. Mixed with the Diatoms there were a few small +_Globigerinoe_, some of the tests and spicules of Radiolarians, and some +sand particles; but these foreign bodies were in too small proportion to +affect the formation as consisting practically of Diatoms alone. On the +4th of February, in lat. 52°, 29' S., long., 71° 36" E., a little to the +north of the Heard Islands, the tow-net, dragging a few fathoms below the +surface, came up nearly filled with a pale yellow gelatinous mass. This +was found to consist entirely of Diatoms of the same species as those +found at the bottom. By far the most abundant was the little bundle of +silicious rods, fastened together loosely at one end, separating from one +another at the other end, and the whole bundle loosely twisted into a +spindle. The rods are hollow, and contain the characteristic endochrome +of the _Diatomaceoe_. Like the _Globigerina_ ooze, then, which it +succeeds to the southward in a band apparently of no great width, the +materials of this silicious deposit are derived entirely from the surface +and intermediate depths. It is somewhat singular that Diatoms did not +appear to be in such large numbers on the surface over the Diatom ooze as +they were a little further north. This may perhaps be accounted for by +our not having struck their belt of depth with the tow-net; or it is +possible that when we found it on the 11th of February the bottom deposit +was really shifted a little to the south by the warm current, the +excessively fine flocculent _débris_ of the Diatoms taking a certain time +to sink. The belt of Diatom ooze is certainly a little further to the +southward in long. 83° E., in the path of the reflux of the Agulhas +current, than in long. 108° E. + +"All along the edge of the ice-pack--everywhere, in fact, to the south of +the two stations--on the 11th of February on our southward voyage, and on +the 3rd of March on our return, we brought up fine sand and grayish mud, +with small pebbles of quartz and felspar, and small fragments of mica- +slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, I +have no doubt, was derived from the surface like the others, but in this +case by the melting of icebergs and the precipitation of foreign matter +contained in the ice. + +"We never saw any trace of gravel or sand, or any material necessarily +derived from land, on an iceberg. Several showed vertical or irregular +fissures filled with discoloured ice or snow; but, when looked at +closely, the discoloration proved usually to be very slight, and the +effect at a distance was usually due to the foreign material filling the +fissure reflecting light less perfectly than the general surface of the +berg. I conceive that the upper surface of one of these great tabular +southern icebergs, including by far the greater part of its bulk, and +culminating in the portion exposed above the surface of the sea, was +formed by the piling up of successive layers of snow during the period, +amounting perhaps to several centuries, during which the ice-cap was +slowly forcing itself over the low land and out to sea over a long extent +of gentle slope, until it reached a depth considerably above 200 fathoms, +when the lower specific weight of the ice caused an upward strain which +at length overcame the cohesion of the mass, and portions were rent off +and floated away. If this be the true history of the formation of these +icebergs, the absence of all land _débris_ in the portion exposed above +the surface of the sea is readily understood. If any such exist, it must +be confined to the lower part of the berg, to that part which has at one +time or other moved on the floor of the ice-cap. + +"The icebergs, when they are first dispersed, float in from 200 to 250 +fathoms. When, therefore, they have been drifted to latitudes of 65° or +64° S., the bottom of the berg just reaches the layer at which the +temperature of the water is distinctly rising, and it is rapidly melted, +and the mud and pebbles with which it is more or less charged are +precipitated. That this precipitation takes place all over the area where +the icebergs are breaking up, constantly, and to a considerable extent, +is evident from the fact of the soundings being entirely composed of such +deposits; for the Diatoms, _Globigerinoe_, and radiolarians are present +on the surface in large numbers; and unless the deposit from the ice were +abundant it would soon be covered and masked by a layer of the exuvia of +surface organisms." + +The observations which have been detailed leave no doubt that the +Antarctic sea bottom, from a little to the south of the fiftieth +parallel, as far as 80° S., is being covered by a fine deposit of +silicious mud, more or less mixed, in some parts, with the ice-borne +_débris_ of polar lands and with the ejections of volcanoes. The +silicious particles which constitute this mud, are derived, in part, from +the diatomaceous plants and radiolarian animals which throng the surface, +and, in part, from the spicula of sponges which live at the bottom. The +evidence respecting the corresponding Arctic area is less complete, but +it is sufficient to justify the conclusion that an essentially similar +silicious cap is being formed around the northern pole. + +There is no doubt that the constituent particles of this mud may +agglomerate into a dense rock, such as that formed at Oran on the shores +of the Mediterranean, which is made up of similar materials. Moreover, in +the case of freshwater deposits of this kind it is certain that the +action of percolating water may convert the originally soft and friable, +fine-grained sandstone into a dense, semi-transparent opaline stone, the +silicious organized skeletons being dissolved, and the silex re-deposited +in an amorphous state. Whether such a metamorphosis as this occurs in +submarine deposits, as well as in those formed in fresh water, does not +appear; but there seems no reason to doubt that it may. And hence it may +not be hazardous to conclude that very ordinary metamorphic agencies may +convert these polar caps into a form of quartzite. + +In the great intermediate zone, occupying some 110° of latitude, which +separates the circumpolar Arctic and Antarctic areas of silicious +deposit, the Diatoms and _Radiolaria_ of the surface water and the +sponges of the bottom do not die out, and, so far as some forms are +concerned, do not even appear to diminish in total number; though, on a +rough estimate, it would appear that the proportion of _Radiolaria_ to +Diatoms is much greater than in the colder seas. Nevertheless the +composition of the deep-sea mud of this intermediate zone is entirely +different from that of the circumpolar regions. + +The first exact information respecting the nature of this mud at depths +greater than 1,000 fathoms was given by Ehrenberg, in the account which +he published in the "Monatsberichte" of the Berlin Academy for the year +1853, of the soundings obtained by Lieut. Berryman, of the United States +Navy, in the North Atlantic, between Newfoundland and the Azores. + +Observations which confirm those of Ehrenberg in all essential respects +have been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter, +and Professor Wyville Thomson, in their earlier cruises; and the +continuation of the _Globigerina_ ooze over the South Pacific has been +proved by the recent work of the _Challenger_, by which it is also shown, +for the first time, that, in passing from the equator to high southern +latitudes, the number and variety of the _Foraminifera_ diminishes, and +even the _Globigerinoe_ become dwarfed. And this result, it will be +observed, is in entire accordance with the fact already mentioned that, +in the sea of Kamschatka, the deep-sea mud was found by Bailey to contain +no calcareous organisms. + +Thus, in the whole of the "intermediate zone," the silicious deposit +which is being formed there, as elsewhere, by the accumulation of sponge- +spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by the +immensely greater amount of calcareous sediment, which arises from the +aggregation of the skeletons of dead _Foraminifera_. The similarity of +the deposit, thus composed of a large percentage of carbonate of lime, +and a small percentage of silex, to chalk, regarded merely as a kind of +rock, which was first pointed out by Ehrenberg,[5] is now admitted on all +hands; nor can it be reasonably doubted, that ordinary metamorphic +agencies are competent to convert the "modern chalk" into hard limestone +or even into crystalline marble. + +[Footnote 5: The following passages in Ehrenberg's memoir on _The +Organisms in the Chalk which are still living_ (1839), are conclusive:-- + +"7. The dawning period of the existing living organic creation, if such a +period is distinguishable (which is doubtful), can only be supposed to +have existed on the other side of, and below, the chalk formation; and +thus, either the chalk, with its widespread and thick beds, must enter +into the series of newer formations; or some of the accepted four great +geological periods, the quaternary, tertiary, and secondary formations, +contain organisms which still live. It is more probable, in the +proportion of 3 to 1, that the transition or primary period is not +different, but that it is only more difficult to examine and understand, +by reason of the gradual and prolonged chemical decomposition and +metamorphosis of many of its organic constituents." + +"10. By the mass-forming _Infasoria_ and _Polythalamia_, secondary are +not distinguishable from tertiary formations; and, from what has been +said, it is possible that, at this very day, rock masses are forming in +the sea, and being raised by volcanic agencies, the constitution of +which, on the whole, is altogether similar to that of the chalk. The +chalk remains distinguishable by its organic remains as a formation, but +not as a kind of rock."] + +Ehrenberg appears to have taken it for granted that the _Globigerinoe_ +and other _Foraminifera_ which are found in the deep-sea mud, live at the +great depths in which their remains are found; and he supports this +opinion by producing evidence that the soft parts of these organisms are +preserved, and may be demonstrated by removing the calcareous matter with +dilute acids. In 1857, the evidence for and against this conclusion +appeared to me to be insufficient to warrant a positive conclusion one +way or the other, and I expressed myself in my report to the Admiralty on +Captain Dayman's soundings in the following terms:-- + +"When we consider the immense area over which this deposit is spread, the +depth at which its formation is going on, and its similarity to chalk, +and still more to such rocks as the marls of Caltanisetta, the question, +whence are all these organisms derived? becomes one of high scientific +interest. + +"Three answers have suggested themselves:-- + +"In accordance with the prevalent view of the limitation of life to +comparatively small depths, it is imagined either: 1, that these +organisms have drifted into their present position from shallower waters; +or 2, that they habitually live at the surface of the ocean, and only +fall down into their present position. + +"1. I conceive that the first supposition is negatived by the extremely +marked zoological peculiarity of the deep-sea fauna. + +"Had the _Globigerinoe_ been drifted into their present position from +shallow water, we should find a very large proportion of the +characteristic inhabitants of shallow waters mixed with them, and this +would the more certainly be the case, as the large _Globigerinoe_, so +abundant in the deep-sea soundings, are, in proportion to their size, +more solid and massive than almost any other _Foraminifera_. But the fact +is that the proportion of other _Foraminifera_ is exceedingly small, nor +have I found as yet, in the deep-sea deposits, any such matters as +fragments of molluscous shells, of _Echini_, &c., which abound in shallow +waters, and are quite as likely to be drifted as the heavy +_Globigerinoe_. Again, the relative proportions of young and fully formed +_Globigerinoe_ seem inconsistent with the notion that they have travelled +far. And it seems difficult to imagine why, had the deposit been +accumulated in this way, _Coscinodisci_ should so almost entirely +represent the _Diatomaceoe_. + +"2. The second hypothesis is far more feasible, and is strongly supported +by the fact that many _Polycistineoe [Radiolaria]_ and _Coscinodisci_ are +well known to live at the surface of the ocean. Mr. Macdonald, Assistant- +Surgeon of H.M.S. _Herald_, now in the South-Western Pacific, has lately +sent home some very valuable observations on living forms of this kind, +met with in the stomachs of oceanic mollusks, and therefore certainly +inhabitants of the superficial layer of the ocean. But it is a singular +circumstance that only one of the forms figured by Mr. Macdonald is at +all like a _Globigerina_, and there are some peculiarities about even +this which make me greatly doubt its affinity with that genus. The form, +indeed, is not unlike that of a _Globigerina_, but it is provided with +long radiating processes, of which I have never seen any trace in +_Globigerina_. Did they exist, they might explain what otherwise is a +great objection to this view, viz., how is it conceivable that the heavy +_Globigerina_ should maintain itself at the surface of the water? + +"If the organic bodies in the deep-sea soundings have neither been +drifted, nor have fallen from above, there remains but one alternative-- +they must have lived and died where they are. + +"Important objections, however, at once suggest themselves to this view. +How can animal life be conceived to exist under such conditions of light, +temperature, pressure, and aeration as must obtain at these vast depths? + +"To this one can only reply that we know for a certainty that even very +highly-organized animals do continue to live at a depth of 300 and 400 +fathoms, inasmuch as they have been dredged up thence; and that the +difference in the amount of light and heat at 400 and at 2,000 fathoms is +probably, so to speak, very far less than the difference in complexity of +organisation between these animals and the humbler _Protozoa_ and +_Protophyta_ of the deep-sea soundings. + +"I confess, though as yet far from regarding it proved that the +_Globigerinoe_ live at these depths, the balance of probabilities seems +to me to incline in that direction. And there is one circumstance which +weighs strongly in my mind. It may be taken as a law that any genus of +animals which is found far back in time is capable of living under a +great variety of circumstances as regards light, temperature, and +pressure. Now, the genus _Globigerina_ is abundantly represented in the +cretaceous epoch, and perhaps earlier. + +"I abstain, however, at present from drawing any positive conclusions, +preferring rather to await the result of more extended observations."[6] + +[Footnote 6: Appendix to Report on Deep-sea Soundings in the Atlantic +Ocean, by Lieut.-Commander Joseph Dayman. 1857.] + +Dr. Wallich, Professor Wyville Thomson, and Dr. Carpenter concluded that +the _Globigerinoe_ live at the bottom. Dr. Wallich writes in 1862--"By +sinking very fine gauze nets to considerable depths, I have repeatedly +satisfied myself that _Globigerina_ does not occur in the superficial +strata of the ocean."[7] Moreover, having obtained certain living star- +fish from a depth of 1,260 fathoms, and found their stomachs full of +"fresh-looking _Globigerinoe_" and their _débris_--he adduces this fact +in support of his belief that the _Globigerinoe_ live at the bottom. + +[Footnote 7: The _North Atlantic Sea-bed_, p. 137.] + +On the other hand, Müller, Haeckel, Major Owen, Mr. Gwyn Jeffries, and +other observers, found that _Globigerinoe_, with the allied genera +_Orbulina_ and _Pulvinulina_, sometimes occur abundantly at the surface +of the sea, the shells of these pelagic forms being not unfrequently +provided with the long spines noticed by Macdonald; and in 1865 and 1866, +Major Owen more especially insisted on the importance of this fact. The +recent work of the _Challenger_ fully confirms Major Owen's statement. In +the paper recently published in the proceedings of the Royal Society,[8] +from which a quotation has already been made, Professor Wyville Thomson +says:-- + +"I had formed and expressed a very strong opinion on the matter. It +seemed to me that the evidence was conclusive that the _Foraminifera_ +which formed the _Globigerina_ ooze lived on the bottom, and that the +occurrence of individuals on the surface was accidental and exceptional; +but after going into the thing carefully, and considering the mass of +evidence which has been accumulated by Mr. Murray, I now admit that I was +in error; and I agree with him that it may be taken as proved that all +the materials of such deposits, with the exception, of course, of the +remains of animals which we now know to live at the bottom at all depths, +which occur in the deposit as foreign bodies, are derived from the +surface. + +[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procured +by the soundings of H.M.S. _Challenger_ during her cruise in the Southern +Seas, in the early part of the year 1874."--_Proceedings of the Royal +Society_, Nov. 26, 1874.] + +"Mr. Murray has combined with a careful examination of the soundings a +constant use of the tow-net, usually at the surface, but also at depths +of from ten to one hundred fathoms; and he finds the closest relation to +exist between the surface fauna of any particular locality and the +deposit which is taking place at the bottom. In all seas, from the +equator to the polar ice, the tow-net contains _Globigerinoe_. They are +more abundant and of a larger size in warmer seas; several varieties, +attaining a large size and presenting marked varietal characters, are +found in the intertropical area of the Atlantic. In the latitude of +Kerguelen they are less numerous and smaller, while further south they +are still more dwarfed, and only one variety, the typical _Globigerina +bulloides_, is represented. The living _Globigerinoe_ from the tow-net +are singularly different in appearance from the dead shells we find at +the bottom. The shell is clear and transparent, and each of the pores +which penetrate it is surrounded by a raised crest, the crest round +adjacent pores coalescing into a roughly hexagonal network, so that the +pores appear to lie at the bottom of a hexagonal pit. At each angle of +this hexagon the crest gives off a delicate flexible calcareous spine, +which is sometimes four or five times the diameter of the shell in +length. The spines radiate symmetrically from the direction of the centre +of each chamber of the shell, and the sheaves of long transparent needles +crossing one another in different directions have a very beautiful +effect. The smaller inner chambers of the shell are entirely filled with +an orange-yellow granular sarcode; and the large terminal chamber usually +contains only a small irregular mass, or two or three small masses run +together, of the same yellow sarcode stuck against one side, the +remainder of the chamber being empty. No definite arrangement and no +approach to structure was observed in the sarcode, and no +differentiation, with the exception of round bright-yellow oil-globules, +very much like those found in some of the radiolarians, which are +scattered, apparently irregularly, in the sarcode. We never have been +able to detect, in any of the large number of _Globigerinoe_ which we +have examined, the least trace of pseudopodia, or any extension, in any +form, of the sarcode beyond the shell. + + * * * * * + +"In specimens taken with the tow-net the spines are very usually absent; +but that is probably on account of their extreme tenuity; they are broken +off by the slightest touch. In fresh examples from the surface, the dots +indicating the origin of the lost spines may almost always be made out +with a high power. There are never spines on the _Globigerinoe_ from the +bottom, even in the shallowest water." + + +There can now be no doubt, therefore, that _Globigerinoe_ live at the top +of the sea; but the question may still be raised whether they do not also +live at the bottom. In favour of this view, it has been urged that the +shells of the _Globigerinoe_ of the surface never possess such thick +walls as those which are fouled at the bottom, but I confess that I doubt +the accuracy of this statement. Again, the occurrence of minute +_Globigerinoe_ in all stages of development, at the greatest depths, is +brought forward as evidence that they live _in situ_. But considering the +extent to which the surface organisms are devoured, without +discrimination of young and old, by _Salpoe_ and the like, it is not +wonderful that shells of all ages should be among the rejectamenta. Nor +can the presence of the soft parts of the body in the shells which form +the _Globigerina_ ooze, and the fact, if it be one, that animals living +at the bottom use them as food, be considered as conclusive evidence that +the _Globigerinoe_ live at the bottom. Such as die at the surface, and +even many of those which are swallowed by other animals, may retain much +of their protoplasmic matter when they reach the depths at which the +temperature sinks to 34° or 32° Fahrenheit, where decomposition must +become exceedingly slow. + +Another consideration appears to me to be in favour of the view that the +_Globigerinoe_ and their allies are essentially surface animals. This is +the fact brought out by the _Challenger's_ work, that they have a +southern limit of distribution, which can hardly depend upon anything but +the temperature of the surface water. And it is to be remarked that this +southern limit occurs at a lower latitude in the Antarctic seas than it +does in the North Atlantic. According to Dr. Wallich ("The North Atlantic +Sea Bed," p. 157) _Globigerina_ is the prevailing form in the deposits +between the Faroe Islands and Iceland, and between Iceland and East +Greenland--or, in other words, in a region of the sea-bottom which lies +altogether north of the parallel of 60° N.; while in the southern seas, +the _Globigerinoe_ become dwarfed and almost disappear between 50° and +55° S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_ +have vanished in 56° N., so that the persistence of the _Globigerina_ +ooze in high latitudes, in the North Atlantic, would seem to depend on +the northward curve of the isothermals peculiar to this region; and it is +difficult to understand how the formation of _Globigerina_ ooze can be +affected by this climatal peculiarity unless it be effected by surface +animals. + +Whatever may be the mode of life of the _Foraminifera_, to which the +calcareous element of the deep-sea "chalk" owes its existence, the fact +that it is the chief and most widely spread material of the sea-bottom in +the intermediate zone, throughout both the Atlantic and Pacific Oceans, +and the Indian Ocean, at depths from a few hundred to over two thousand +fathoms, is established. But it is not the only extensive deposit which +is now taking place. In 1853, Count Pourtalès, an officer of the United +States Coast Survey, which has done so much for scientific hydrography, +observed, that the mud forming the sea-bottom at depths of one hundred +and fifty fathoms, in 31° 32' N., 79° 35' W., off the Coast of Florida, +was "a mixture, in about equal proportions, of _Globigerinoe_ and black +sand, probably greensand, as it makes a green mark when crushed on +paper." Professor Bailey, examining these grains microscopically, found +that they were casts of the interior cavities of _Foraminifera_, +consisting of a mineral known as _Glauconite_, which is a silicate of +iron and alumina. In these casts the minutest cavities and finest tubes +in the Foraminifer were sornetilnes reproduced in solid counterparts of +the glassy mineral, while the calcareous original had been entirely +dissolved away. + +Contemporaneously with these observations, the indefatigable Ehrenberg +had discovered that the "greensands" of the geologist were largely made +up of casts of a similar character, and proved the existence of +_Foraminifera_ at a very ancient geological epoch, by discovering such +casts in a greensand of Lower Silurian age, which occurs near St. +Petersburg. + +Subsequently, Messrs. Parker and Jones discovered similar casts in +process of formation, the original shell not having disappeared, in +specimens of the sea-bottom of the Australian seas, brought home by the +late Professor Jukes. And the _Challenger_ has observed a deposit of a +similar character in the course of the Agulhas current, near the Cape of +Good Hope, and in some other localities not yet defined. + +It would appear that this infiltration of _Foraminifera_ shells with +_Glauconite_ does not take place at great depths, but rather in what may +be termed a sublittoral region, ranging from a hundred to three hundred +fathoms. It cannot be ascribed to any local cause, for it takes place, +not only over large areas in the Gulf of Mexico and the Coast of Florida, +but in the South Atlantic and in the Pacific. But what are the conditions +which determine its occurrence, and whence the silex, the iron, and the +alumina (with perhaps potash and some other ingredients in small +quantity) of which the _Glauconite_ is composed, proceed, is a point on +which no light has yet been thrown. For the present we must be content +with the fact that, in certain areas of the "intermediate zone," +greensand is replacing and representing the primitively calcareo- +silicious ooze. + +The investigation of the deposits which are now being formed in the basin +of the Mediterranean, by the late Professor Edward Forbes, by Professor +Williamson and more recently by Dr. Carpenter, and a comparison of the +results thus obtained with what is known of the surface fauna, have +brought to light the remarkable fact, that while the surface and the +shallows abound with _Foraminifera_ and other calcareous shelled +organisms, the indications of life become scanty at depths beyond 500 or +600 fathoms, while almost all traces of it disappear at greater depths, +and at 1,000 to 2,000 fathoms the bottom is covered with a fine clay. + +Dr. Carpenter has discussed the significance of this remarkable fact, and +he is disposed to attribute the absence of life at great depths, partly +to the absence of any circulation of the water of the Mediterranean at +such depths, and partly to the exhaustion of the oxygen of the water by +the organic matter contained in the fine clay, which he conceives to be +formed by the finest particles of the mud brought down by the rivers +which flow into the Mediterranean. + +However this may be, the explanation thus offered of the presence of the +fine mud, and of the absence of organisms which ordinarily live at the +bottom, does not account for the absence of the skeletons of the +organisms which undoubtedly abound at the surface of the Mediterranean; +and it would seem to have no application to the remarkable fact +discovered by the _Challenger_, that in the open Atlantic and Pacific +Oceans, in the midst of the great intermediate zone, and thousands of +miles away from the embouchure of any river, the sea-bottom, at depths +approaching to and beyond 3,000 fathoms, no longer consists of +_Globigerina_ ooze, but of an excessively fine red clay. + +Professor Thomson gives the following account of this capital +discovery:-- + +"According to our present experience, the deposit of _Globigerina_ ooze +is limited to water of a certain depth, the extreme limit of the pure +characteristic formation being placed at a depth of somewhere about 2,250 +fathoms. Crossing from these shallower regions occupied by the ooze into +deeper soundings, we find, universally, that the calcareous formation +gradually passes into, and is finally replaced by, an extremely fine pure +clay, which occupies, speaking generally, all depths below 2,500 fathoms, +and consists almost entirely of a silicate of the red oxide of iron and +alumina. The transition is very slow, and extends over several hundred +fathoms of increasing depth; the shells gradually lose their sharpness of +outline, and assume a kind of 'rotten' look and a brownish colour, and +become more and more mixed with a fine amorphous red-brown powder, which +increases steadily in proportion until the lime has almost entirely +disappeared. This brown matter is in the finest possible state of +subdivision, so fine that when, after sifting it to separate any +organisms it might contain, we put it into jars to settle, it remained +for days in suspension, giving the water very much the appearance and +colour of chocolate. + +"In indicating the nature of the bottom on the charts, we came, from +experience and without any theoretical considerations, to use three terms +for soundings in deep water. Two of these, Gl. oz. and r. cl., were very +definite, and indicated strongly-marked formations, with apparently but +few characters in common; but we frequently got soundings which we could +not exactly call '_Globigerina_ ooze' or 'red clay,' and before we were +fully aware of the nature of these, we were in the habit of indicating +them as 'grey ooze' (gr. oz.) We now recognise the 'grey ooze' as an +intermediate stage between the _Globigerina_ ooze and the red clay; we +find that on one side, as it were, of an ideal line, the red clay +contains more and more of the material of the calcareous ooze, while on +the other, the ooze is mixed with an increasing proportion of 'red clay.' + +"Although we have met with the same phenomenon so frequently, that we +were at length able to predict the nature of the bottom from the depth of +the soundings with absolute certainty for the Atlantic and the Southern +Sea, we had, perhaps, the best opportunity of observing it in our first +section across the Atlantic, between Teneriffe and St. Thomas. The first +four stations on this section, at depths from 1,525 to 2,220 fathoms, +show _Globigerina_ ooze. From the last of these, which is about 300 miles +from Teneriffe, the depth gradually increases to 2,740 fathoms at 500, +and 2,950 fathoms at 750 miles from Teneriffe. The bottom in these two +soundings might have been called 'grey ooze,' for although its nature has +altered entirely from the _Globigerina_ ooze, the red clay into which it +is rapidly passing still contains a considerable admixture of carbonate +of lime. + +"The depth goes on increasing to a distance of 1,150 miles from +Teneriffe, when it reaches 3,150 fathoms; there the clay is pure and +smooth, and contains scarcely a trace of lime. From this great depth the +bottom gradually rises, and, with decreasing depth, the grey colour and +the calcareous composition of the ooze return. Three soundings in 2,050, +1,900, and 1,950 fathoms on the 'Dolphin Rise' gave highly characteristic +examples of the _Globigerina_ formation. Passing from the middle plateau +of the Atlantic into the western trough, with depths a little over 3,000 +fathoms, the red clay returned in all its purity; and our last sounding, +in 1,420 fathoms, before reaching Sombrero, restored the _Globigerina_ +ooze with its peculiar associated fauna. + +"This section shows also the wide extension and the vast geological +importance of the red clay formation. The total distance from Teneriffe +to Sombrero is about 2,700 miles. Proceeding from east to west, we have-- + +About 80 miles of volcanic mud and sand, + " 350 " _Globigerina_ ooze, + " 1,050 " red clay, + " 330 " _Globigerina_ ooze, + " 850 " red clay, + " 40 " _Globigerina_ ooze; + +giving a total of 1,900 miles of red clay to 720 miles of _Globigerina_ +ooze. + +"The nature and origin of this vast deposit of clay is a question of the +very greatest interest; and although I think there can be no doubt that +it is in the main solved, yet some matters of detail are still involved +in difficulty. My first impression was that it might be the most minutely +divided material, the ultimate sediment produced by the disintegration of +the land, by rivers and by the action of the sea on exposed coasts, and +held in suspension and distributed by ocean currents, and only making +itself manifest in places unoccupied by the _Globigerina_ ooze. Several +circumstances seemed, however, to negative this mode of origin. The +formation seemed too uniform: wherever we met with it, it had the same +character, and it only varied in composition in containing less or more +carbonate of lime. + +"Again, the were gradually becoming more and more convinced that all the +important elements of the _Globigerina_ ooze lived on the surface, and it +seemed evident that, so long as the condition on the surface remained the +same, no alteration of contour at the bottom could possibly prevent its +accumulation; and the surface conditions in the Mid-Atlantic were very +uniform, a moderate current of a very equal temperature passing +continuously over elevations and depressions, and everywhere yielding to +the tow-net the ooze-forming _Foraminifera_ in the same proportion. The +Mid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, the +shells of these are constantly mixed with the _Globigerina_ ooze, +sometimes in number sufficient to make up a considerable portion of its +bulk. It is clear that these shells must fall in equal numbers upon the +red clay, but scarcely a trace of one of them is ever brought up by the +dredge on the red clay area. It might be possible to explain the absence +of shell-secreting animals living on the bottom, on the supposition that +the nature of the deposit was injurious to them; but then the idea of a +current sufficiently strong to sweep them away is negatived by the +extreme fineness of the sediment which is being laid down; the absence of +surface shells appears to be intelligible only on the supposition that +they are in some way removed. + +"We conclude, therefore, that the 'red clay' is not an additional +substance introduced from without, and occupying certain depressed +regions on account of some law regulating its deposition, but that it is +produced by the removal, by some means or other, over these areas, of the +carbonate of lime, which forms probably about 98 per cent. of the +material of the _Globigerina_ ooze. We can trace, indeed, every +successive stage in the removal of the carbonate of lime in descending +the slope of the ridge or plateau where the _Globigerina_ ooze is +forming, to the region of the clay. We find, first, that the shells of +pteropods and other surface _Mollusca_ which are constantly falling on +the bottom, are absent, or, if a few remain, they are brittle and yellow, +and evidently decaying rapidly. These shells of _Mollusca_ decompose more +easily and disappear sooner than the smaller, and apparently more +delicate, shells of rhizopods. The smaller _Foraminifera_ now give way, +and are found in lessening proportion to the larger; the coccoliths first +lose their thin outer border and then disappear; and the clubs of the +rhabdoliths get worn out of shape, and are last seen, under a high power, +as infinitely minute cylinders scattered over the field. The larger +_Foraminifera_ are attacked, and instead of being vividly white and +delicately sculptured, they become brown and worn, and finally they break +up, each according to its fashion; the chamber-walls of _Globigerina_ +fall into wedge-shaped pieces, which quickly disappear, and a thick rough +crust breaks away from the surface of _Orbulina_, leaving a thin inner +sphere, at first beautifully transparent, but soon becoming opaque and +crumbling away. + +"In the meantime the proportion of the amorphous 'red clay' to the +calcareous elements of all kinds increases, until the latter disappear, +with the exception of a few scattered shells of the larger +_Foraminifera_, which are still found even in the most characteristic +samples of the 'red clay.' + +"There seems to be no room left for doubt that the red clay is +essentially the insoluble residue, the _ash_, as it were, of the +calcareous organisms which form the _Globigerina_ ooze, after the +calcareous matter has been by some means removed. An ordinary mixture of +calcareous _Foraminifera_ with the shells of pteropods, forming a fair +sample of _Globigerina_ ooze from near St. Thomas, was carefully washed, +and subjected by Mr. Buchanan to the action of weak acid; and he found +that there remained after the carbonate of lime had been removed, about 1 +per cent. of a reddish mud, consisting of silica, alumina, and the red +oxide of iron. This experiment has been frequently repeated with +different samples of _Globigerina_ ooze, and always with the result that +a small proportion of a red sediment remains, which possesses all the +characters of the red clay." + + * * * * * + +"It seems evident from the observations here recorded, that _clay_, which +we have hitherto looked upon as essentially the product of the +disintegration of older rocks, may be, under certain circumstances, an +organic formation like chalk; that, as a matter of fact, an area on the +surface of the globe, which we have shown to be of vast extent, although +we are still far from having ascertained its limits, is being covered by +such a deposit at the present day. + +"It is impossible to avoid associating such a formation with the fine, +smooth, homogeneous clays and schists, poor in fossils, but showing worm- +tubes and tracks, and bunches of doubtful branching things, such as +Oldhamia, silicious sponges, and thin-shelled peculiar shrimps. Such +formations, more or less metamorphosed, are very familiar, especially to +the student of palaeozoic geology, and they often attain a vast thickness. +One is inclined, from the great resemblance between them in composition +and in the general character of the included fauna, to suspect that these +may be organic formations, like the modern red clay of the Atlantic and +Southern Sea, accumulations of the insoluble ashes of shelled creatures. + +"The dredging in the red clay on the 13th of March was usually rich. The +bag contained examples, those with calcareous shells rather stunted, of +most of the characteristic deep-water groups of the Southern Sea, +including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha, +Pourtalesia_, and one or two _Mollusca_. This is, however, very rarely +the case. Generally the red clay is barren, or contains only a very small +number of forms." + +It must be admitted that it is very difficult, at present, to frame any +satisfactory explanation of the mode of origin of this singular deposit +of red clay. + +I cannot say that the theory put forward tentatively, and with much +reservation by Professor Thomson, that the calcareous matter is dissolved +out by the relatively fresh water of the deep currents from the Antarctic +regions, appears satisfactory to me. Nor do I see my way to the +acceptance of the suggestion of Dr. Carpenter, that the red clay is the +result of the decomposition of previously-formed greensand. At present +there is no evidence that greensand casts are ever formed at great +depths; nor has it been proved that _Glauconite_ is decomposable by the +agency of water and carbonic acid. + +I think it probable that we shall have to wait some time for a sufficient +explanation of the origin of the abyssal red clay, no less than for that +of the sublittoral greensand in the intermediate zone. But the importance +of the establishment of the fact that these various deposits are being +formed in the ocean, at the present day, remains the same; whether its +_rationale_ be understood or not. + +For, suppose the globe to be evenly covered with sea, to a depth say of a +thousand fathoms--then, whatever might be the mineral matter composing +the sea-bottom, little or no deposit would be formed upon it, the +abrading and denuding action of water, at such a depth, being exceedingly +slight. + +Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceous +plants, such as those which now exist in the deep-sea, to be introduced: +they would be distributed according to the same laws as at present, the +sponges (and possibly some of the _Foraminifera_), covering the bottom, +while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, would +increase and multiply in the surface waters. In accordance with the +existing state of things, the _Radiolaria_ and Diatoms would have a +universal distribution, the latter gathering most thickly in the polar +regions, while the _Foraminifera_ would be largely, if not exclusively, +confined to the intermediate zone; and, as a consequence of this +distribution, a bed of "chalk" would begin to form in the intermediate +zone, while caps of silicious rock would accumulate on the circumpolar +regions. + +Suppose, further, that a part of the intermediate area were raised to +within two or three hundred fathoms of the surface--for anything that we +know to the contrary, the change of level might determine the +substitution of greensand for the "chalk"; while, on the other hand, if +part of the same area were depressed to three thousand fathoms, that +change might determine the substitution of a different silicate of +alumina and iron--namely, clay--for the "chalk" that would otherwise be +formed. + +If the _Challenger_ hypothesis, that the red clay is the residue left by +dissolved _Foraminiferous_ skeletons, is correct, then all these deposits +alike would be directly, or indirectly, the product of living organisms. +But just as a silicious deposit may be metamorphosed into opal or +quartzite, and chalk into marble, so known metamorphic agencies may +metamorphose clay into schist, clay-slate, slate, gneiss, or even +granite. And thus, by the agency of the lowest and simplest of organisms, +our imaginary globe might be covered with strata, of all the chief kinds +of rock of which the known crust of the earth is composed, of indefinite +thickness and extent. + +The bearing of the conclusions which are now either established, or +highly probable, respecting the origin of silicious, calcareous, and +clayey rocks, and their metamorphic derivatives, upon the archaeology of +the earth, the elucidation of which is the ultimate object of the +geologist, is of no small importance. + +A hundred years ago the singular insight of Linnaeus enabled him to say +that "fossils are not the children but the parents of rocks,"[9] and the +whole effect of the discoveries made since his time has been to compile a +larger and larger commentary upon this text. It is, at present, a +perfectly tenable hypothesis that all siliceous and calcareous rocks are +either directly, or indirectly, derived from material which has, at one +time or other, formed part of the organized framework of living +organisms. Whether the same generalization may be extended to aluminous +rocks, depends upon the conclusion to be drawn from the facts respecting +the red clay areas brought to light by the _Challenger_. If we accept the +view taken by Wyville Thomson and his colleagues--that the red clay is +the residuum left after the calcareous matter of the _Globigerinoe_ ooze +has been dissolved away--then clay is as much a product of life as +limestone, and all known derivatives of clay may have formed part of +animal bodies. + +[Footnote 9: "Petrificata montium calcariorum non filii sed parentes +sunt, cum omnis calx oriatur ab animalibus."--_Systema Naturae_, Ed. xii., +t. iii., p. 154. It must be recollected that Linnaeus included silex, as +well as limestone, under the name of "calx," and that he would probably +have arranged Diatoms among animals, as part of "chaos." Ehrenberg quotes +another even more pithy passage, which I have not been able to find in +any edition of the _Systema_ accessible to me: "Sic lapides ab +animalibus, nec vice versa. Sic runes saxei non primaevi, sed temporis +filiae."] + +So long as the _Globigerinoe_;, actually collected at the surface, have +not been demonstrated to contain the elements of clay, the _Challenger_ +hypothesis, as I may term it, must be accepted with reserve and +provisionally, but, at present, I cannot but think that it is more +probable than any other suggestion which has been made. + +Accepting it provisionally, we arrive at the remarkable result that all +the chief known constituents of the crust of the earth may have formed +part of living bodies; that they may be the "ash" of protoplasm; that the +"_rupes saxei_" are not only _"temporis,"_ but "_vitae filiae_"; and, +consequently, that the time during which life has been active on the +globe may be indefinitely greater than the period, the commencement of +which is marked by the oldest known rocks, whether fossiliferous or +unfossiliferous. + +And thus we are led to see where the solution of a great problem and +apparent paradox of geology may lie. Satisfactory evidence now exists +that some animals in the existing world have been derived by a process of +gradual modification from pre-existing forms. It is undeniable, for +example, that the evidence in favour of the derivation of the horse from +the later tertiary _Hipparion_, and that of the _Hipparion_ from +_Anchitherium_, is as complete and cogent as such evidence can reasonably +be expected to be; and the further investigations into the history of the +tertiary mammalia are pushed, the greater is the accumulation of evidence +having the same tendency. So far from palaeontology lending no support to +the doctrine of evolution--as one sees constantly asserted--that +doctrine, if it had no other support, would have been irresistibly forced +upon us by the palaeontological discoveries of the last twenty years. + +If, however, the diverse forms of life which now exist have been produced +by the modification of previously-existing less divergent forms, the +recent and extinct species, taken as a whole, must fall into series which +must converge as we go back in time. Hence, if the period represented by +the rocks is greater than, or co-extensive with, that during which life +has existed, we ought, somewhere among the ancient formations, to arrive +at the point to which all these series converge, or from which, in other +words, they have diverged--the primitive undifferentiated protoplasmic +living things, whence the two great series of plants and animals have +taken their departure. + +But, as a matter of fact, the amount of convergence of series, in +relation to the time occupied by the deposition of geological formations, +is extraordinarily small. Of all animals the higher _Vertebrata_ are the +most complex; and among these the carnivores and hoofed animals +(_Ungulata_) are highly differentiated. Nevertheless, although the +different lines of modification of the _Carnivora_ and those of the +_Ungulata_, respectively, approach one another, and, although each group +is represented by less differentiated forms in the older tertiary rocks +than at the present day, the oldest tertiary rocks do not bring us near +the primitive form of either. If, in the same way, the convergence of the +varied forms of reptiles is measured against the time during which their +remains are preserved--which is represented by the whole of the tertiary +and mesozoic formations--the amount of that convergence is far smaller +than that of the lines of mammals between the present time and the +beginning of the tertiary epoch. And it is a broad fact that, the lower +we go in the scale of organization, the fewer signs are there of +convergence towards the primitive form from whence all must have +diverged, if evolution be a fact. Nevertheless, that it is a fact in some +cases, is proved, and I, for one, have not the courage to suppose that +the mode in which some species have taken their origin is different from +that in which the rest have originated. + +What, then, has become of all the marine animals which, on the hypothesis +of evolution, must have existed in myriads in those seas, wherein the +many thousand feet of Cambrian and Laurentian rocks now devoid, or almost +devoid, of any trace of life were deposited? + +Sir Charles Lyell long ago suggested that the azoic character of these +ancient formations might be due to the fact that they had undergone +extensive metamorphosis; and readers of the "Principles of Geology" will +be familiar with the ingenious manner in which he contrasts the theory of +the Gnome, who is acquainted only with the interior of the earth, with +those of ordinary philosophers, who know only its exterior. + +The metamorphism contemplated by the great modern champion of rational +geology is, mainly, that brought about by the exposure of rocks to +subterranean heat; and where no such heat could be shown to have +operated, his opponents assumed that no metamorphosis could have taken +place. But the formation of greensand, and still more that of the "red +clay" (if the _Challenger_ hypothesis be correct) affords an insight into +a new kind of metamorphosis--not igneous, but aqueous--by which the +primitive nature of a deposit may be masked as completely as it can be by +the agency of heat. And, as Wyville Thomson suggests, in the passage I +have quoted above (p. 17), it further enables us to assign a new cause +for the occurrence, so puzzling hitherto, of thousands of feet of +unfossiliferous fine-grained schists and slates, in the midst of +formations deposited in seas which certainly abounded in life. If the +great deposit of "red clay" now forming in the eastern valley of the +Atlantic were metamorphosed into slate and then upheaved, it would +constitute an "azoic" rock of enormous extent. And yet that rock is now +forming in the midst of a sea which swarms with living beings, the great +majority of which are provided with calcareous or silicious shells and +skeletons; and, therefore, are such as, up to this time, we should have +termed eminently preservable. + +Thus the discoveries made by the _Challenger_ expedition, like all recent +advances in our knowledge of the phenomena of biology, or of the changes +now being effected in the structure of the surface of the earth, are in +accordance with and lend strong support to, that doctrine of +Uniformitarianism, which, fifty years ago, was held only by a small +minority of English geologists--Lyell, Scrope, and De la Beche--but now, +thanks to the long-continued labours of the first two, and mainly to +those of Sir Charles Lyell, has gradually passed from the position of a +heresy to that of catholic doctrine. + +Applied within the limits of the time registered by the known fraction of +the crust of the earth, I believe that uniformitarianism is unassailable. +The evidence that, in the enormous lapse of time between the deposition +of the lowest Laurentian strata and the present day, the forces which +have modified the surface of the crust of the earth were different in +kind, or greater in the intensity of their action, than those which are +now occupied in the same work, has yet to be produced. Such evidence as +we possess all tends in the contrary direction, and is in favour of the +same slow and gradual changes occurring then as now. + +But this conclusion in nowise conflicts with the deductions of the +physicist from his no less clear and certain data. It may be certain that +this globe has cooled down from a condition in which life could not have +existed; it may be certain that, in so cooling, its contracting crust +must have undergone sudden convulsions, which were to our earthquakes as +an earthquake is to the vibration caused by the periodical eruption of a +Geyser; but in that case, the earth must, like other respectable parents, +have sowed her wild oats, and got through her turbulent youth, before we, +her children, have any knowledge of her. + +So far as the evidence afforded by the superficial crust of the earth +goes, the modern geologist can, _ex animo_, repeat the saying of Hutton, +"We find no vestige of a beginning--no prospect of an end." However, he +will add, with Hutton, "But in thus tracing back the natural operations +which have succeeded each other, and mark to us the course of time past, +we come to a period in which we cannot see any further." And if he seek +to peer into the darkness of this period, he will welcome the light +proffered by physics and mathematics. + + + +IV + + +YEAST + +[1871] + +It has been known, from time immemorial, that the sweet liquids which may +be obtained by expressing the juices of the fruits and stems of various +plants, or by steeping malted barley in hot water, or by mixing honey +with water--are liable to undergo a series of very singular changes, if +freely exposed to the air and left to themselves, in warm weather. +However clear and pellucid the liquid may have been when first prepared, +however carefully it may have been freed, by straining and filtration, +from even the finest visible impurities, it will not remain clear. After +a time it will become cloudy and turbid; little bubbles will be seen +rising to the surface, and their abundance will increase until the liquid +hisses as if it were simmering on the fire. By degrees, some of the solid +particles which produce the turbidity of the liquid collect at its +surface into a scum, which is blown up by the emerging air-bubbles into a +thick, foamy froth. Another moiety sinks to the bottom, and accumulates +as a muddy sediment, or "lees." + +When this action has continued, with more or less violence, for a certain +time, it gradually moderates. The evolution of bubbles slackens, and +finally comes to an end; scum and lees alike settle at the bottom, and +the fluid is once more clear and transparent. But it has acquired +properties of which no trace existed in the original liquid. Instead of +being a mere sweet fluid, mainly composed of sugar and water, the sugar +has more or less completely disappeared; and it has acquired that +peculiar smell and taste which we call "spirituous." Instead of being +devoid of any obvious effect upon the animal economy, it has become +possessed of a very wonderful influence on the nervous system; so that in +small doses it exhilarates, while in larger it stupefies, and may even +destroy life. + +Moreover, if the original fluid is put into a still, and heated +moderately, the first and last product of its distillation is simple +water; while, when the altered fluid is subjected to the same process, +the matter which is first condensed in the receiver is found to be a +clear, volatile substance, which is lighter than water, has a pungent +taste and smell, possesses the intoxicating powers of the fluid in an +eminent degree, and takes fire the moment it is brought in contact with a +flame. The Alchemists called this volatile liquid, which they obtained +from wine, "spirits of wine," just as they called hydrochloric acid +"spirits of salt," and as we, to this day, call refined turpentine +"spirits of turpentine." As the "spiritus," or breath, of a man was +thought to be the most refined and subtle part of him, the intelligent +essence of man was also conceived as a sort of breath, or spirit; and, by +analogy, the most refined essence of anything was called its "spirit." +And thus it has come about that we use the same word for the soul of man +and for a glass of gin. + +At the present day, however, we even more commonly use another name for +this peculiar liquid--namely, "alcohol," and its origin is not less +singular. The Dutch physician, Van Helmont, lived in the latter part of +the sixteenth and the beginning of the seventeenth century--in the +transition period between alchemy and chemistry--and was rather more +alchemist than chemist. Appended to his "Opera Omnia," published in 1707, +there is a very needful "Clavis ad obscuriorum sensum referendum," in +which the following passage occurs.-- + +"ALCOHOL.--Chymicis est liquor aut pulvis summé subtilisatus, vocabulo +Orientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_ +speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat +... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorum +cancri summé subtilisatus _alcohol_ audit, haud aliter ac spiritus +rectificatissimi _alcolisati_ dicuntur." + +Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, so +late as the middle of the last century, the English lexicographer, Nathan +Bailey, defines "alcohol" as "the pure substance of anything separated +from the more gross, a very fine and impalpable powder, or a very pure, +well-rectified spirit." But, by the time of the publication of +Lavoisier's "Traité Elémentaire de Chimie," in 1789, the term "alcohol," +"alkohol," or "alkool" (for it is spelt in all three ways), which Van +Helmont had applied primarily to a fine powder, and only secondarily to +spirits of wine, had lost its primary meaning altogether; and, from the +end of the last century until now, it has, I believe, been used +exclusively as the denotation of spirits of wine, and bodies chemically +allied to that substance. + +The process which gives rise to alcohol in a saccharine fluid is known +tones as "fermentation"; a term based upon the apparent boiling up or +"effervescence" of the fermenting liquid, and of Latin origin. + +Our Teutonic cousins call the same process "gähren," "gäsen," "göschen," +and "gischen"; but, oddly enough, we do not seem to have retained their +verb or their substantive denoting the action itself, though we do use +names identical with, or plainly derived from, theirs for the scum and +lees. These are called, in Low German, "gäscht" and "gischt"; in Anglo- +Saxon, "gest," "gist," and "yst," whence our "yeast." Again, in Low +German and in Anglo-Saxon there is another name for yeast, having the +form "barm," or "beorm"; and, in the Midland Counties, "barm" is the name +by which yeast is still best known. In High German, there is a third name +for yeast, "hefe," which is not represented in English, so far as I know. + +All these words are said by philologers to be derived from roots +expressive of the intestine motion of a fermenting substance. Thus "hefe" +is derived from "heben," to raise; "barm" from "beren" or "bären," to +bear up; "yeast," "yst," and "gist," have all to do with seething and +foam, with "yeasty" waves, and "gusty" breezes. + +The same reference to the swelling up of the fermenting substance is seen +in the Gallo-Latin terms "levure" and "leaven." + +It is highly creditable to the ingenuity of our ancestors that the +peculiar property of fermented liquids, in virtue of which they "make +glad the heart of man," seems to have been known in the remotest periods +of which we have any record. All savages take to alcoholic fluids as if +they were to the manner born. Our Vedic forefathers intoxicated +themselves with the juice of the "soma"; Noah, by a not unnatural +reaction against a superfluity of water, appears to have taken the +earliest practicable opportunity of qualifying that which he was obliged +to drink; and the ghosts of the ancient Egyptians were solaced by +pictures of banquets in which the wine-cup passes round, graven on the +walls of their tombs. A knowledge of the process of fermentation, +therefore, was in all probability possessed by the prehistoric +populations of the globe; and it must have become a matter of great +interest even to primaeval wine-bibbers to study the methods by which +fermented liquids could be surely manufactured. No doubt it was soon +discovered that the most certain, as well as the most expeditious, way of +making a sweet juice ferment was to add to it a little of the scum, or +lees, of another fermenting juice. And it can hardly be questioned that +this singular excitation of fermentation in one fluid, by a sort of +infection, or inoculation, of a little ferment taken from some other +fluid, together with the strange swelling, foaming, and hissing of the +fermented substance, must have always attracted attention from the more +thoughtful. Nevertheless, the commencement of the scientific analysis of +the phenomena dates from a period not earlier than the first half of the +seventeenth century. + +At this time, Van Helmont made a first step, by pointing out that the +peculiar hissing and bubbling of a fermented liquid is due, not to the +evolution of common air (which he, as the inventor of the term "gas," +calls "gas ventosum"), but to that of a peculiar kind of air such as is +occasionally met with in caves, mines, and wells, and which he calls "gas +sylvestre." + +But a century elapsed before the nature of this "gas sylvestre," or, as +it was afterwards called, "fixed air," was clearly determined, and it was +found to be identical with that deadly "choke-damp" by which the lives of +those who descend into old wells, or mines, or brewers' vats, are +sometimes suddenly ended; and with the poisonous aëriform fluid which is +produced by the combustion of charcoal, and now goes by the name of +carbonic acid gas. + +During the same time it gradually became evident that the presence of +sugar was essential to the production of alcohol and the evolution of +carbonic acid gas, which are the two great and conspicuous products of +fermentation. And finally, in 1787, the Italian chemist, Fabroni, made +the capital discovery that the yeast ferment, the presence of which is +necessary to fermentation, is what he termed a "vegeto-animal" substance; +that is, a body which gives of ammoniacal salts when it is burned, and +is, in other ways, similar to the gluten of plants and the albumen and +casein of animals. + +These discoveries prepared the way for the illustrious Frenchman, +Lavoisier, who first approached the problem of fermentation with a +complete conception of the nature of the work to be done. The words in +which he expresses this conception, in the treatise on elementary +chemistry to which reference has already been made, mark the year 1789 as +the commencement of a revolution of not less moment in the world of +science than that which simultaneously burst over the political world, +and soon engulfed Lavoisier himself in one of its mad eddies. + +"We may lay it down as an incontestable axiom that, in all the operations +of art and nature, nothing is created; an equal quantity of matter exists +both before, and after the experiment: the quality and quantity of the +elements remain precisely the same, and nothing takes place beyond +changes and modifications in the combinations of these elements. Upon +this principle the whole art of performing chemical experiments depends; +we must always suppose an exact equality between the elements of the body +examined and those of the products of its analysis. + +"Hence, since from must of grapes we procure alcohol and carbonic acid, I +have an undoubted right to suppose that must consists of carbonic acid +and alcohol. From these premisses we have two modes of ascertaining what +passes during vinous fermentation: either by determining the nature of, +and the elements which compose, the fermentable substances; or by +accurately examining the products resulting from fermentation; and it is +evident that the knowledge of either of these must lead to accurate +conclusions concerning the nature and composition of the other. From +these considerations it became necessary accurately to determine the +constituent elements of the fermentable substances; and for this purpose +I did not make use of the compound juices of fruits, the rigorous +analysis of which is perhaps impossible, but made choice of sugar, which +is easily analysed, and the nature of which I have already explained. +This substance is a true vegetable oxyd, with two bases, composed of +hydrogen and carbon, brought to the state of an oxyd by means of a +certain proportion of oxygen; and these three elements are combined in +such a way that a very slight force is sufficient to destroy the +equilibrium of their connection." + +After giving the details of his analysis of sugar and of the products of +fermentation, Lavoisier continues:-- + +"The effect of the vinous fermentation upon sugar is thus reduced to the +mere separation of its elements into two portions; one part is oxygenated +at the expense of the other, so as to form carbonic acid; while the other +part, being disoxygenated in favour of the latter, is converted into the +combustible substance called alkohol; therefore, if it were possible to +re-unite alkohol and carbonic acid together, we ought to form sugar."[1] + +[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated by +Robert Kerr. Second Edition, 1793 (pp. 186-196).] + +Thus Lavoisier thought he had demonstrated that the carbonic acid and the +alcohol which are produced by the process of fermentation, are equal in +weight to the sugar which disappears; but the application of the more +refined methods of modern chemistry to the investigation of the products +of fermentation by Pasteur, in 1860, proved that this is not exactly +true, and that there is a deficit of from 5 to 7 per cent of the sugar +which is not covered by the alcohol and carbonic acid evolved. The +greater part of this deficit is accounted for by the discovery of two +substances, glycerine and succinic acid, of the existence of which +Lavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent. +still remains to be made good. According to Pasteur, it has been +appropriated by the yeast, but the fact that such appropriation takes +place cannot be said to be actually proved. + +However this may be, there can be no doubt that the constituent elements +of fully 98 per cent. of the sugar which has vanished during fermentation +have simply undergone rearrangement; like the soldiers of a brigade, who +at the word of command divide themselves into the independent regiments +to which they belong. The brigade is sugar, the regiments are carbonic +acid, succinic acid, alcohol, and glycerine. + +From the time of Fabroni, onwards, it has been admitted that the agent by +which this surprising rearrangement of the particles of the sugar is +effected is the yeast. But the first thoroughly conclusive evidence of +the necessity of yeast for the fermentation of sugar was furnished by +Appert, whose method of preserving perishable articles of food excited so +much attention in France at the beginning of this century. Gay-Lussac, in +his "Mémoire sur la Fermentation,"[2] alludes to Appert's method of +preserving beer-wort unfermented for an indefinite time, by simply +boiling the wort and closing the vessel in which the boiling fluid is +contained, in such a way as thoroughly to exclude air; and he shows that, +if a little yeast be introduced into such wort, after it has cooled, the +wort at once begins to ferment, even though every precaution be taken to +exclude air. And this statement has since received full confirmation from +Pasteur. + +[Footnote 2: _Annales de Chimie_, 1810.] + +On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amply +proved that air may be allowed to have free access to beer-wort, without +exciting fermentation, if only efficient precautions are taken to prevent +the entry of particles of yeast along with the air. + +Thus, the truth that the fermentation of a simple solution of sugar in +water depends upon the presence of yeast, rests upon an unassailable +foundation; and the inquiry into the exact nature of the substance which +possesses such a wonderful chemical influence becomes profoundly +interesting. + +The first step towards the solution of this problem was made two +centuries ago by the patient and painstaking Dutch naturalist, +Leeuwenhoek, who in the year 1680 wrote thus:-- + +"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis per +materiam pellucidam fluitantibus, quarm cerevisiam esse censui, constare +observavi: vidi etiam evidentissime, unumquemque hujus fermenti globulum +denuo ex sex distinctis globulis constare, accurate eidem quantitate et +formae, cui globulis sanguinis nostri, respondentibus. + +"Verum talis mihi de horum origine et formatione conceptus formabam; +globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se +constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam +cerevisiam vocare licet, refrigescente, multos ex minimis particulis in +cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae +sexta pars est globuli faecis, et iterum sex ex hisce globulis +conjungi."[3] + +[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.] + +Thus Leeuwenhoek discovered that yeast consists of globules floating in a +fluid; but he thought that they were merely the starchy particles of the +grain from which the wort was made, rearranged. He discovered the fact +that yeast had a definite structure, but not the meaning of the fact. A +century and a half elapsed, and the investigation of yeast was +recommenced almost simultaneously by Cagniard de la Tour in France, and +by Schwann and Kützing in Germany. The French observer was the first to +publish his results; and the subject received at his hands and at those +of his colleague, the botanist Turpin, full and satisfactory +investigation. + +The main conclusions at which they arrived are these. The globular, or +oval, corpuscles which float so thickly in the yeast as to make it muddy, +though the largest are not more than one two-thousandth of an inch in +diameter, and the smallest may measure less than one seven-thousandth of +an inch, are living organisms. They multiply with great rapidity by +giving off minute buds, which soon attain the size of their parent, and +then either become detached or remain united, forming the compound +globules of which Leeuwenhoek speaks, though the constancy of their +arrangement in sixes existed only in the worthy Dutchman's imagination. + +It was very soon made out that these yeast organisms, to which Turpin +gave the name of _Torula cerevisioe_, were more nearly allied to the +lower Fungi than to anything else. Indeed Turpin, and subsequently +Berkeley and Hoffmann, believed that they had traced the development of +the _Torula_ into the well-known and very common mould--the _Penicillium +glaucum_. Other observers have not succeeded in verifying these +statements; and my own observations lead me to believe, that while the +connection between _Torula_ and the moulds is a very close one, it is of +a different nature from that which has been supposed. I have never been +able to trace the development of _Torula_ into a true mould; but it is +quite easy to prove that species of true mould, such as _Penicillium_, +when sown in an appropriate nidus, such as a solution of tartrate of +ammonia and yeast-ash, in water, with or without sugar, give rise to +_Toruloe_, similar in all respects to _T. cerevisioe_, except that they +are, on the average, smaller. Moreover, Bail has observed the development +of a _Torula_ larger than _T. cerevisioe_, from a _Mucor_, a mould allied +to _Penicillium_. + +It follows, therefore, that the _Toruloe_, or organisms of yeast, are +veritable plants; and conclusive experiments have proved that the power +which causes the rearrangement of the molecules of the sugar is +intimately connected with the life and growth of the plant. In fact, +whatever arrests the vital activity of the plant also prevents it from +exciting fermentation. + +Such being the facts with regard to the nature of yeast, and the changes +which it effects in sugar, how are they to be accounted for? Before +modern chemistry had come into existence, Stahl, stumbling, with the +stride of genius, upon the conception which lies at the bottom of all +modern views of the process, put forward the notion that the ferment, +being in a state of internal motion, communicated that motion to the +sugar, and thus caused its resolution into new substances. And Lavoisier, +as we have seen, adopts substantially the same view. But Fabroni, full of +the then novel conception of acids and bases and double decompositions, +propounded the hypothesis that sugar is an oxide with two bases, and the +ferment a carbonate with two bases; that the carbon of the ferment unites +with the oxygen of the sugar, and gives rise to carbonic acid; while the +sugar, uniting with the nitrogen of the ferment, produces a new substance +analogous to opium. This is decomposed by distillation, and gives rise to +alcohol. Next, in 1803, Thénard propounded a hypothesis which partakes +somewhat of the nature of both Stahl's and Fabroni's views. "I do not +believe with Lavoisier," he says, "that all the carbonic acid formed +proceeds from the sugar. How, in that case, could we conceive the action +of the ferment on it? I think that the first portions of the acid are due +to a combination of the carbon of the ferment with the oxygen of the +sugar, and that it is by carrying off a portion of oxygen from the last +that the ferment causes the fermentation to commence--the equilibrium +between the principles of the sugar being disturbed, they combine afresh +to form carbonic acid and alcohol." + +The three views here before us may be familiarly exemplified by supposing +the sugar to be a card-house. According to Stahl, the ferment is somebody +who knocks the table, and shakes the card-house down; according to +Fabroni, the ferment takes out some cards, but puts others in their +places; according to Thénard, the ferment simply takes a card out of the +bottom story, the result of which is that all the others fall. + +As chemistry advanced, facts came to light which put a new face upon +Stahl's hypothesis, and gave it a safer foundation than it previously +possessed. The general nature of these phenomena may be thus stated:--A +body, A, without giving to, or taking from, another body B, any material +particles, causes B to decompose into other substances, C, D, E, the sum +of the weights of which is equal to the weight of B, which decomposes. +Thus, bitter almonds contain two substances, amygdalin and synaptase, +which can be extracted, in a separate state, from the bitter almonds. The +amygdalin thus obtained, if dissolved in water, undergoes no change; but +if a little synaptase be added to the solution, the amygdalin splits up +into bitter almond oil, prussic acid, and a kind of sugar. + +A short time after Cagniard de la Tour discovered the yeast plant, +Liebig, struck with the similarity between this and other such processes +and the fermentation of sugar, put forward the hypothesis that yeast +contains a substance which acts upon sugar, as synaptase acts upon +amygdalin. And as the synaptase is certainly neither organized nor alive, +but a mere chemical substance, Liebig treated Cagniard de la Tour's +discovery with no small contempt, and, from that time to the present, has +steadily repudiated the notion that the decomposition of the sugar is, in +any sense, the result of the vital activity of the _Torula_. But, though +the notion that the _Torula_ is a creature which eats sugar and excretes +carbonic acid and alcohol, which is not unjustly ridiculed in the most +surprising paper that ever made its appearance in a grave scientific +journal,[4] may be untenable, the fact that the _Toruloe_ are alive, and +that yeast does not excite fermentation unless it contains living +_Toruloe_, stands fast. Moreover, of late years, the essential +participation of living organisms in fermentation other than the +alcoholic, has been clearly made out by Pasteur and other chemists. + +[Footnote 4: "Das enträthselte Geheimniss der geistigen Gährung +(Vorlänfige briefliche Mittheilung)" is the title of an anonymous +contribution to Wöhler and Liebig's _Annalen der Pharmacie_ for 1839, in +which a somewhat Rabelaisian imaginary description of the organisation of +the "yeast animals" and of the manner in which their functions are +performed, is given with a circumstantiality worthy of the author of +_Gulliver's Travels_. As a specimen of the writer's humour, his account +of what happens when fermentation comes to an end may suffice. "Sobald +nämlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich +gegenseitig selbst auf, was durch eine eigene Manipulation geschieht; +alles wird verdant bis auf die Eier, welche unverändert durch den +Darmkanal hineingehen; man hat zuletzt wieder gährungsfähige Hefe, +nämlich den Saamen der Thiere, der übrig bleibt."] However, it may be +asked, is there any necessary opposition between the so-called "vital" +and the strictly physico-chemical views of fermentation? It is quite +possible that the living _Torula_ may excite fermentation in sugar, +because it constantly produces, as an essential part of its vital +manifestations, some substance which acts upon the sugar, just as the +synaptase acts upon the amygdalin. Or it may be, that, without the +formation of any such special substance, the physical condition of the +living tissue of the yeast plant is sufficient to effect that small +disturbance of the equilibrium of the particles of the sugar, which +Lavoisier thought sufficient to effect its decomposition. + +Platinum in a very fine state of division--known as platinum black, or +_noir de platine_--has the very singular property of causing alcohol to +change into acetic acid with great rapidity. The vinegar plant, which is +closely allied to the yeast plant, has a similar effect upon dilute +alcohol, causing it to absorb the oxygen of the air, and become converted +into vinegar; and Liebig's eminent opponent, Pasteur, who has done so +much for the theory and the practice of vinegar-making, himself suggests +that in this case-- + +"La cause du phénomène physique qui accompagne la vie de la plante réside +dans un état physique propre, analogue à celui du noir de platine. Mais +il est essentiel de remarquer que cet état physique de la plante est +étroitement lié avec la vie de cette plante."[5] + +[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.] + +Now, if the vinegar plant gives rise to the oxidation of alcohol, on +account of its merely physical constitution, it is at any rate possible +that the physical constitution of the yeast plant may exert a decomposing +influence on sugar. + +But, without presuming to discuss a question which leads us into the very +arcana of chemistry, the present state of speculation upon the _modus +operandi_ of the yeast plant in producing fermentation is represented, on +the one hand, by the Stahlian doctrine, supported by Liebig, according to +which the atoms of the sugar are shaken into new combinations either +directly by the _Toruloe_, or indirectly, by some substance formed by +them; and, on the other hand, by the Thénardian doctrine, supported by +Pasteur, according to which the yeast plant assimilates part of the +sugar, and, in so doing, disturbs the rest, and determines its resolution +into the products of fermentation. Perhaps the two views are not so much +opposed as they seem at first sight to be. + +But the interest which attaches to the influence of the yeast plants upon +the medium in which they live and grow does not arise solely from its +bearing upon the theory of fermentation. So long ago as 1838, Turpin +compared the _Toruloe_ to the ultimate elements of the tissues of animals +and plants--"Les organes élémentaires de leurs tissus, comparables aux +petits végétaux des levures ordinaires, sont aussi les décompositeurs des +substances qui les environnent." + +Almost at the same time, and, probably, equally guided by his study of +yeast, Schwann was engaged in those remarkable investigations into the +form and development of the ultimate structural elements of the tissues +of animals, which led him to recognise their fundamental identity with +the ultimate structural elements of vegetable organisms. + +The yeast plant is a mere sac, or "cell," containing a semi-fluid matter, +and Schwann's microscopic analysis resolved all living organisms, in the +long run, into an aggregation of such sacs or cells, variously modified; +and tended to show, that all, whatever their ultimate complication, begin +their existence in the condition of such simple cells. + +In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_ +as a "cell"; and, in a remarkable note to the passage in which he refers +to the yeast plant, Schwann says:-- + +"I have been unable to avoid mentioning fermentation, because it is the +most fully and exactly known operation of cells, and represents, in the +simplest fashion, the process which is repeated by every cell of the +living body." + +In other words, Schwann conceives that every cell of the living body +exerts an influence on the matter which surrounds and permeates it, +analogous to that which a _Torula_ exerts on the saccharine solution by +which it is bathed. A wonderfully suggestive thought, opening up views of +the nature of the chemical processes of the living body, which have +hardly yet received all the development of which they are capable. + +Kant defined the special peculiarity of the living body to be that the +parts exist for the sake of the whole and the whole for the sake of the +parts. But when Turpin and Schwann resolved the living body into an +aggregation of quasi-independent cells, each, like a _Torula_, leading +its own life and having its own laws of growth and development, the +aggregation being dominated and kept working towards a definite end only +by a certain harmony among these units, or by the superaddition of a +controlling apparatus, such as a nervous system, this conception ceased +to be tenable. The cell lives for its own sake, as well as for the sake +of the whole organism; and the cells which float in the blood, live at +its expense, and profoundly modify it, are almost as much independent +organisms as the _Toruloe_ which float in beer-wort. + +Schwann burdened his enunciation of the "cell theory" with two false +suppositions; the one, that the structures he called "nucleus"[6] and +"cell-wall" are essential to a cell; the other, that cells are usually +formed independently of other cells; but, in 1839, it was a vast and +clear gain to arrive at the conception, that the vital functions of all +the higher animals and plants are the resultant of the forces inherent in +the innumerable minute cells of which they are composed, and that each of +them is, itself, an equivalent of one of the lowest and simplest of +independent living beings--the _Torula_. + +[Footnote 6: Later investigations have thrown an entirely new light upon +the structure and the functional importance of the nucleus; and have +proved that Schwann did not over-estimate its importance. 1894.] + +From purely morphological investigations, Turpin and Schwann, as we have +seen, arrived at the notion of the fundamental unity of structure of +living beings. And, before long, the researches of chemists gradually led +up to the conception of the fundamental unity of their composition. + +So far back as 1803, Thénard pointed out, in most distinct terms, the +important fact that yeast contains a nitrogenous "animal" substance; and +that such a substance is contained in all ferments. Before him, Fabroni +and Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulder +endeavoured to demonstrate that a peculiar substance, which he called +"protein," was essentially characteristic of living matter. + +In 1846, Payen writes:-- + +"Enfin, une loi sans exception me semble apparaître dans les faits +nombreux que j'ai observés et conduire à envisager sous un nouveau jour +la vie végétale; si je ne m'abuse, tout ce que dans les tissus végétaux +la vue directe où amplifiée nous permet de discerner sous la forme de +cellules et de vaisseaux, ne représente autre chose que les enveloppes +protectrices, les réservoirs et les conduits, à l'aide desquels les corps +animés qui les secrètent et les façonnent, se logent, puisent et +charrient leurs aliments, déposent et isolent les matières excrétées." + +And again:-- + +"Afin de compléter aujourd'hui l'énoncé du fait général, je rappellerai +que les corps, doué des fonctions accomplies dans les tissus des plantes, +sont formés des éléments qui constituent, en proportion peu variable, les +organismes animaux; qu'ainsi l'on est conduit à reconnaître une immense +unité de composition élémentaire dans tous les corps vivants de la +nature."[7] + +[Footnote 7: Mém. sur les Développements des Végétaux, &c.--_Mém. +Présentées_. ix. 1846.] + +In the year (1846) in which these remarkable passages were published, the +eminent German botanist, Von Mohl invented the word "protoplasm," as a +name for one portion of those nitrogenous contents of the cells of living +plants, the close chemical resemblance of which to the essential +constituents of living animals is so strongly indicated by Payen. And +through the twenty-five years that have passed, since the matter of life +was first called protoplasm, a host of investigators, among whom Cohn, +Max Schulze, and Kühne must be named as leaders, have accumulated +evidence, morphological, physiological, and chemical, in favour of that +"immense unité de composition élémentaire dans tous les corps vivants de +la nature," into which Payen had, so early, a clear insight. + +As far back as 1850, Cohn wrote, apparently without any knowledge of what +Payen had said before him:-- + +"The protoplasm of the botanist, and the contractile substance and +sarcode of the zoologist, must be, if not identical, yet in a high degree +analogous substances. Hence, from this point of view, the difference +between animals and plants consists in this; that, in the latter, the +contractile substance, as a primordial utricle, is enclosed within an +inert cellulose membrane, which permits it only to exhibit an internal +motion, expressed by the phenomena of rotation and circulation, while, in +the former, it is not so enclosed. The protoplasm in the form of the +primordial utricle is, as it were, the animal element in the plant, but +which is imprisoned, and only becomes free in the animal; or, to strip +off the metaphor which obscures simple thought, the energy of organic +vitality which is manifested in movement is especially exhibited by a +nitrogenous contractile substance, which in plants is limited and +fettered by an inert membrane, in animals not so."[8] + +[Footnote 8: Cohn, "Ueber Protococcus pluvialis," in the _Nova Acta_ for +1850.] + +In 1868, thinking that an untechnical statement of the views current +among the leaders of biological science might be interesting to the +general public, I gave a lecture embodying them in Edinburgh. Those who +have not made the mistake of attempting to approach biology, either by +the high _à priori_ road of mere philosophical speculation, or by the +mere low _à posteriori_ lane offered by the tube of a microscope, but +have taken the trouble to become acquainted with well-ascertained facts +and with their history, will not need to be told that in what I had to +say "as regards protoplasm" in my lecture "On the Physical Basis of Life" +(Vol. I. of these Essays, p. 130), there was nothing new; and, as I hope, +nothing that the present state of knowledge does not justify us in +believing to be true. Under these circumstances, my surprise may be +imagined, when I found, that the mere statement of facts and of views, +long familiar to me as part of the common scientific property of +Continental workers, raised a sort of storm in this country, not only by +exciting the wrath of unscientific persons whose pet prejudices they +seemed to touch, but by giving rise to quite superfluous explosions on +the part of some who should have been better informed. + +Dr. Stirling, for example, made my essay the subject of a special +critical lecture,[9] which I have read with much interest, though, I +confess, the meaning of much of it remains as dark to me as does the +"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr. +Stirling's method of dealing with the subject is peculiar. "Protoplasm" +is a question of history, so far as it is a name; of fact, so far as it +is a thing. Dr. Stirling, has not taken the trouble to refer to the +original authorities for his history, which is consequently a travesty; +and still less has he concerned himself with looking at the facts, but +contents himself with taking them also at second-hand. A most amusing +example of this fashion of dealing with scientific statements is +furnished by Dr. Stirling's remarks upon my account of the protoplasm of +the nettle hair. That account was drawn up from careful and often- +repeated observation of the facts. Dr. Stirling thinks he is offering a +valid criticism, when he says that my valued friend Professor Stricker +gives a somewhat different statement about protoplasm. But why in the +world did not this distinguished Hegelian look at a nettle hair for +himself, before venturing to speak about the matter at all? Why trouble +himself about what either Stricker or I say, when any tyro can see the +facts for himself, if he is provided with those not rare articles, a +nettle and a microscope? But I suppose this would have been +"_Aufklärung_"--a recurrence to the base common-sense philosophy of the +eighteenth century, which liked to see before it believed, and to +understand before it criticised Dr. Stirling winds up his paper with the +following paragraph:-- + +[Footnote 9: Subsequently published under the title of "As regards +Protoplasm."] + +"In short, the whole position of Mr. Huxley, (1) that all organisms +consist alike of the same life-matter, (2) which life-matter is, for its +part, due only to chemistry, must be pronounced untenable--nor less +untenable (3) the materialism he would found on it." + +The paragraph contains three distinct assertions concerning my views, and +just the same number of utter misrepresentations of them. That which I +have numbered (1) turns on the ambiguity of the word "same," for a +discussion of which I would refer Dr. Stirling to a great hero of +"_Aufklärung_" Archbishop Whately; statement number (2) is, in my +judgment, absurd, and certainly I have never said anything resembling it; +while, as to number (3), one great object of my essay was to show that +what is called "materialism" has no sound philosophical basis! + +As we have seen, the study of yeast has led investigators face to face +with problems of immense interest in pure chemistry, and in animal and +vegetable morphology. Its physiology is not less rich in subjects for +inquiry. Take, for example, the singular fact that yeast will increase +indefinitely when grown in the dark, in water containing only tartrate of +ammonia a small percentage of mineral salts and sugar. Out of these +materials the _Toruloe_ will manufacture nitrogenous protoplasm, +cellulose, and fatty matters, in any quantity, although they are wholly +deprived of those rays of the sun, the influence of which is essential to +the growth of ordinary plants. There has been a great deal of speculation +lately, as to how the living organisms buried beneath two or three +thousand fathoms of water, and therefore in all probability almost +deprived of light, live. If any of them possess the same powers as yeast +(and the same capacity for living without light is exhibited by some +other fungi) there would seem to be no difficulty about the matter. + +Of the pathological bearings of the study of yeast, and other such +organisms, I have spoken elsewhere. It is certain that, in some animals, +devastating epidemics are caused by fungi of low order--similar to those +of which _Torula_ is a sort of offshoot. It is certain that such diseases +are propagated by contagion and infection, in just the same way as +ordinary contagious and infectious diseases are propagated. Of course, it +does not follow from this, that all contagious and infectious diseases +are caused by organisms of as definite and independent a character as the +_Torula_; but, I think, it does follow that it is prudent and wise to +satisfy one's self in each particular case, that the "germ theory" cannot +and will not explain the facts, before having recourse to hypotheses +which have no equal support from analogy. + + + +V + + +ON THE FORMATION OF COAL + +[1870] + +The lumps of coal in a coal-scuttle very often have a roughly cubical +form. If one of them be picked out and examined with a little care, it +will be found that its six sides are not exactly alike. Two opposite +sides are comparatively smooth and shining, while the other four are much +rougher, and are marked by lines which run parallel with the smooth +sides. The coal readily splits along these lines, and the split surfaces +thus formed are parallel with the smooth faces. In other words, there is +a sort of rough and incomplete stratification in the lump of coal, as if +it were a book, the leaves of which had stuck together very closely. + +Sometimes the faces along which the coal splits are not smooth, but +exhibit a thin layer of dull, charred-looking substance, which is known +as "mineral charcoal." + +Occasionally one of the faces of a lump of coal will present impressions, +which are obviously those of the stem, or leaves, of a plant; but though +hard mineral masses of pyrites, and even fine mud, may occur here and +there, neither sand nor pebbles are met with. + +When the coal burns, the chief ultimate products of its combustion are +carbonic acid, water, and ammoniacal products, which escape up the +chimney; and a greater or less amount of residual earthy salts, which +take the form of ash. These products are, to a great extent, such as +would result from the burning of so much wood. + +These properties of coal may be made out without any very refined +appliances, but the microscope reveals something more. Black and opaque +as ordinary coal is, slices of it become transparent if they are cemented +in Canada balsam, and rubbed down very thin, in the ordinary way of +making thin sections of non-transparent bodies. But as the thin slices, +made in this way, are very apt to crack and break into fragments, it is +better to employ marine glue as the cementing material. By the use of +this substance, slices of considerable size and of extreme thinness and +transparency may be obtained.[1] + +[Footnote 1: My assistant in the Museum of Practical Geology, Mr. Newton, +invented this excellent method of obtaining thin slices of coal.] + +Now let us suppose two such slices to be prepared from our lump of coal-- +one parallel with the bedding, the other perpendicular to it; and let us +call the one the horizontal, and the other the vertical, section. The +horizontal section will present more or less rounded yellow patches and +streaks, scattered irregularly through the dark brown, or blackish, +ground substance; while the vertical section will exhibit mere elongated +bars and granules of the same yellow materials, disposed in lines which +correspond, roughly, with the general direction of the bedding of the +coal. + +This is the microscopic structure of an ordinary piece of coal. But if a +great series of coals, from different localities and seams, or even from +different parts of the same seam, be examined, this structure will be +found to vary in two directions. In the anthracitic, or stone-coals, +which burn like coke, the yellow matter diminishes, and the ground +substance becomes more predominant, blacker, and more opaque, until it +becomes impossible to grind a section thin enough to be translucent; +while, on the other hand, in such as the "Better-Bed" coal of the +neighbourhood of Bradford, which burns with much flame, the coal is of a +far lighter, colour and transparent sections are very easily obtained. In +the browner parts of this coal, sharp eyes will readily detect multitudes +of curious little coin-shaped bodies, of a yellowish brown colour, +embedded in the dark brown ground substance. On the average, these little +brown bodies may have a diameter of about one-twentieth of an inch. They +lie with their flat surfaces nearly parallel with the two smooth faces of +the block in which they are contained; and, on one side of each, there +may be discerned a figure, consisting of three straight linear marks, +which radiate from the centre of the disk, but do not quite reach its +circumference. In the horizontal section these disks are often converted +into more or less complete rings; while in the vertical sections they +appear like thick hoops, the sides of which have been pressed together. +The disks are, therefore, flattened bags; and favourable sections show +that the three-rayed marking is the expression of three clefts, which +penetrate one wall of the bag. + +The sides of the bags are sometimes closely approximated; but, when the +bags are less flattened, their cavities are, usually, filled with +numerous, irregularly rounded, hollow bodies, having the same kind of +wall as the large ones, but not more than one seven-hundredth of an inch +in diameter. + +In favourable specimens, again, almost the whole ground substance appears +to be made up of similar bodies--more or less carbonized or blackened-- +and, in these, there can be no doubt that, with the exception of patches +of mineral charcoal, here and there, the whole mass of the coal is made +up of an accumulation of the larger and of the smaller sacs. + +But, in one and the same slice, every transition can be observed from +this structure to that which has been described as characteristic of +ordinary coal. The latter appears to rise out of the former, by the +breaking-up and increasing carbonization of the larger and the smaller +sacs. And, in the anthracitic coals, this process appears to have gone to +such a length, as to destroy the original structure altogether, and to +replace it by a completely carbonized substance. + +Thus coal may be said, speaking broadly, to be composed of two +constituents: firstly, mineral charcoal; and, secondly, coal proper. The +nature of the mineral charcoal has long since been determined. Its +structure shows it to consist of the remains of the stems and leaves of +plants, reduced a little more than their carbon. Again, some of the coal +is made up of the crushed and flattened bark, or outer coat, of the stems +of plants, the inner wood of which has completely decayed away. But what +I may term the "saccular matter" of the coal, which, either in its +primary or in its degraded form constitutes by far the greater part of +all the bituminous coals I have examined, is certainly not mineral +charcoal; nor is its structure that of any stem or leaf. Hence its real +nature is at first by no means apparent, and has been the subject of much +discussion. + +The first person who threw any light upon the problem, as far as I have +been able to discover, was the well-known geologist, Professor Morris. It +is now thirty-four years since he carefully described and figured the +coin-shaped bodies, or larger sacs, as I have called them, in a note +appended to the famous paper "On the Coalbrookdale Coal-Field," published +at that time, by the present President of the Geological Society, Mr. +Prestwich. With much sagacity, Professor Morris divined the real nature +of these bodies, and boldly affirmed them to be the spore-cases of a +plant allied to the living club-mosses. + +But discovery sometimes makes a long halt; and it is only a few years +since Mr. Carruthers determined the plant (or rather one of the plants) +which produces these spore-cases, by finding the discoidal sacs still +adherent to the leaves of the fossilized cone which produced them. He +gave the name of _Flemingites gracilis_ to the plant of which the cones +form a part. The branches and stem of this plant are not yet certainly +known, but there is no sort of doubt that it was closely allied to the +_Lepidodendron_, the remains of which abound in the coal formation. The +_Lepidodendra_ were shrubs and trees which put one more in mind of an +_Araucaria_ than of any other familiar plant; and the ends of the +fruiting branches were terminated by cones, or catkins, somewhat like the +bodies so named in a fir, or a willow. These conical fruits, however, did +not produce seeds; but the leaves of which they were composed bore upon +their surfaces sacs full of spores or sporangia, such as those one sees +on the under surface of a bracken leaf. Now, it is these sporangia of the +Lepidodendroid plant _Flemingites_ which were identified by Mr. +Carruthers with the free sporangia described by Professor Morris, which +are the same as the large sacs of which I have spoken. And, more than +this, there is no doubt that the small sacs are the spores, which were +originally contained in the sporangia. + +The living club-mosses are, for the most part, insignificant and creeping +herbs, which, superficially, very closely resemble true mosses, and none +of them reach more than two or three feet in height. But, in their +essential structure, they very closely resemble the earliest +Lepidodendroid trees of the coal: their stems and leaves are similar; so +are their cones; and no less like are the sporangia and spores; while +even in their size, the spores of the _Lepidodendron_ and those of the +existing _Lycopodium_, or club-moss, very closely approach one another. + +Thus, the singular conclusion is forced upon us, that the greater and the +smaller sacs of the "Better-Bed" and other coals, in which the primitive +structure is well preserved, are simply the sporangia and spores of +certain plants, many of which were closely allied to the existing club- +mosses. And if, as I believe, it can be demonstrated that ordinary coal +is nothing but "saccular" coal which has undergone a certain amount of +that alteration which, if continued, would convert it into anthracite; +then, the conclusion is obvious, that the great mass of the coal we burn +is the result of the accumulation of the spores and spore-cases of +plants, other parts of which have furnished the carbonized stems and the +mineral charcoal, or have left their impressions on the surfaces of the +layer. + +Of the multitudinous speculations which, at various times, have been +entertained respecting the origin and mode of formation of coal, several +appear to be negatived, and put out of court, by the structural facts the +significance of which I have endeavoured to explain. These facts, for +example, do not permit us to suppose that coal is an accumulation of +peaty matter, as some have held. + +Again, the late Professor Quekett was one of the first observers who gave +a correct description of what I have termed the "saccular" structure of +coal; and, rightly perceiving that this structure was something quite +different from that of any known plant, he imagined that it proceeded +from some extinct vegetable organism which was peculiarly abundant +amongst the coal-forming plants. But this explanation is at once shown to +be untenable when the smaller and the larger sacs are proved to be spores +or sporangia. + +Some, once more, have imagined that coal was of submarine origin; and +though the notion is amply and easily refuted by other considerations, it +may be worth while to remark, that it is impossible to comprehend how a +mass of light and resinous spores should have reached the bottom of the +sea, or should have stopped in that position if they had got there. + +At the same time, it is proper to remark that I do not presume to suggest +that all coal must needs have the same structure; or that there may not +be coals in which the proportions of wood and spores, or spore-cases, are +very different from those which I have examined. All I repeat is, that +none of the coals which have come under my notice have enabled me to +observe such a difference. But, according to Principal Dawson, who has so +sedulously examined the fossil remains of plants in North America, it is +otherwise with the vast accumulations of coal in that country. + +"The true coal," says Dr. Dawson, "consists principally of the flattened +bark of Sigillarioid and other trees, intermixed with leaves of Ferns and +_Cordaites_, and other herbaceous _débris_, and with fragments of decayed +wood, constituting 'mineral charcoal,' all these materials having +manifestly alike grown and accumulated where we find them."[2] + +[Footnote 2: _Acadian Geology_, 2nd edition, p. 135.] + +When I had the pleasure of seeing Principal Dawson in London last summer, +I showed him my sections of coal, and begged him to re-examine some of +the American coals on his return to Canada, with an eye to the presence +of spores and sporangia, such as I was able to show him in our English +and Scotch coals. He has been good enough to do so; and in a letter dated +September 26th, 1870, he informs me that-- + +"Indications of spore-cases are rare, except in certain coarse shaly +coals and portions of coals, and in the roofs of the seams. The most +marked case I have yet met with is the shaly coal referred to as +containing _Sporangites_ in my paper on the conditions of accumulation of +coal ("Journal of the Geological Society," vol. xxii. pp. 115, 139, and +165). The purer coals certainly consist principally of cubical tissues +with some true woody matter, and the spore-cases, &c., are chiefly in the +coarse and shaly layers. This is my old doctrine in my two papers in the +"Journal of the Geological Society," and I see nothing to modify it. Your +observations, however, make it probable that the frequent _clear spots_ +in the cannels are spore-cases." + +Dr. Dawson's results are the more remarkable, as the numerous specimens +of British coal, from various localities, which I have examined, tell one +tale as to the predominance of the spore and sporangium element in their +composition; and as it is exactly in the finest and purest coals, such as +the "Better-Bed" coal of Lowmoor, that the spores and sporangia obviously +constitute almost the entire mass of the deposit. + +Coal, such as that which has been described, is always found in sheets, +or "seams," varying from a fraction of an inch to many feet in thickness, +enclosed in the substance of the earth at very various depths, between +beds of rock of different kinds. As a rule, every seam of coal rests upon +a thicker, or thinner, bed of clay, which is known as "under-clay." These +alternations of beds of coal, clay, and rock may be repeated many times, +and are known as the "coal-measures"; and in some regions, as in South +Wales and in Nova Scotia, the coal-measures attain a thickness of twelve +or fourteen thousand feet, and enclose eighty or a hundred seams of coal, +each with its under-clay, and separated from those above and below by +beds of sandstone and shale. + +The position of the beds which constitute the coal-measures is infinitely +diverse. Sometimes they are tilted up vertically, sometimes they are +horizontal, sometimes curved into great basins; sometimes they come to +the surface, sometimes they are covered up by thousands of feet of rock. +But, whatever their present position, there is abundant and conclusive +evidence that every under-clay was once a surface soil. Not only do +carbonized root-fibres frequently abound in these under-clays; but the +stools of trees, the trunks of which are broken off and confounded with +the bed of coal, have been repeatedly found passing into radiating roots, +still embedded in the under-clay. On many parts of the coast of England, +what are commonly known as "submarine forests" are to be seen at low +water. They consist, for the most part, of short stools of oak, beech, +and fir-trees, still fixed by their long roots in the bed of blue clay in +which they originally grew. If one of these submarine forest beds should +be gradually depressed and covered up by new deposits, it would present +just the same characters as an under-clay of the coal, if the +_Sigillaria_ and _Lepidodendron_ of the ancient world were substituted +for the oak, or the beech, of our own times. + +In a tropical forest, at the present day, the trunks of fallen trees, and +the stools of such trees as may have been broken by the violence of +storms, remain entire for but a short time. Contrary to what might be +expected, the dense wood of the tree decays, and suffers from the ravages +of insects, more swiftly than the bark. And the traveller, setting his +foot on a prostrate trunk, finds that it is a mere shell, which breaks +under his weight, and lands his foot amidst the insects, or the reptiles, +which have sought food or refuge within. + +The trees of the coal forests present parallel conditions. When the +fallen trunks which have entered into the composition of the bed of coal +are identifiable, they are mere double shells of bark, flattened together +in consequence of the destruction of the woody core; and Sir Charles +Lyell and Principal Dawson discovered, in the hollow stools of coal trees +of Nova Scotia, the remains of snails, millipedes, and salamander-like +creatures, embedded in a deposit of a different character from that which +surrounded the exterior of the trees. Thus, in endeavouring to comprehend +the formation of a seam of coal, we must try to picture to ourselves a +thick forest, formed for the most part of trees like gigantic club- +mosses, mares'-tails, and tree-ferns, with here and there some that had +more resemblance to our existing yews and fir-trees. We must suppose +that, as the seasons rolled by, the plants grew and developed their +spores and seeds; that they shed these in enormous quantities, which +accumulated on the ground beneath; and that, every now and then, they +added a dead frond or leaf; or, at longer intervals, a rotten branch, or +a dead trunk, to the mass. + +A certain proportion of the spores and seeds no doubt fulfilled their +obvious function, and, carried by the wind to unoccupied regions, +extended the limits of the forest; many might be washed away by rain into +streams, and be lost; but a large portion must have remained, to +accumulate like beech-mast, or acorns, beneath the trees of a modern +forest. + +But, in this case it may be asked, why does not our English coal consist +of stems and leaves to a much greater extent than it does? What is the +reason of the predominance of the spores and spore-cases in it? + +A ready answer to this question is afforded by the study of a living +full-grown club-moss. Shake it upon a piece of paper, and it emits a +cloud of fine dust, which falls over the paper, and is the well-known +Lycopodium powder. Now this powder used to be, and I believe still is, +employed for two objects which seem, at first sight, to have no +particular connection with one another. It is, or was, employed in making +lightning, and in making pills. The coats of the spores contain so much +resinous matter, that a pinch of Lycopodium powder, thrown through the +flame of a candle, burns with an instantaneous flash, which has long done +duty for lightning on the stage. And the same character makes it a +capital coating for pills; for the resinous powder prevents the drug from +being wetted by the saliva, and thus bars the nauseous flavour from the +sensitive papilla; of the tongue. + +But this resinous matter, which lies in the walls of the spores and +sporangia, is a substance not easily altered by air and water, and hence +tends to preserve these bodies, just as the bituminized cerecloth +preserves an Egyptian mummy; while, on the other hand, the merely woody +stem and leaves tend to rot, as fast as the wood of the mummy's coffin +has rotted. Thus the mixed heap of spores, leaves, and stems in the coal- +forest would be persistently searched by the long-continued action of air +and rain; the leaves and stems would gradually be reduced to little but +their carbon, or, in other words, to the condition of mineral charcoal in +which we find them; while the spores and sporangia remained as a +comparatively unaltered and compact residuum. + +There is, indeed, tolerably clear evidence that the coal must, under some +circumstances, have been converted into a substance hard enough to be +rolled into pebbles, while it yet lay at the surface of the earth; for in +some seams of coal, the courses of rivulets, which must have been living +water, while the stratum in which their remains are found was still at +the surface, have been observed to contain rolled pebbles of the very +coal through which the stream has cut its way. + +The structural facts are such as to leave no alternative but to adopt the +view of the origin of such coal as I have described, which has just been +stated; but, happily, the process is not without analogy at the present +day. I possess a specimen of what is called "white coal" from Australia. +It is an inflammable material, burning with a bright flame and having +much the consistence and appearance of oat-cake, which, I am informed +covers a considerable area. It consists, almost entirely, of a compacted +mass of spores and spore-cases. But the fine particles of blown sand +which are scattered through it, show that it must have accumulated, +subaërially, upon the surface of a soil covered by a forest of +cryptogamous plants, probably tree-ferns. + +As regards this important point of the subaërial region of coal, I am +glad to find myself in entire accordance with Principal Dawson, who bases +his conclusions upon other, but no less forcible, considerations. In a +passage, which is the continuation of that already cited, he writes:-- + +"(3) The microscopical structure and chemical composition of the beds of +cannel coal and earthy bitumen, and of the more highly bituminous and +carbonaceous shale, show them to have been of the nature of the fine +vegetable mud which accumulates in the ponds and shallow lakes of modern +swamps. When such tine vegetable sediment is mixed, as is often the case, +with clay, it becomes similar to the bituminous limestone and calcareo- +bituminous shales of the coal-measures. (4) A few of the under-clays, +which support beds of coal, are of the nature of the vegetable mud above +referred to; but the greater part are argillo-arenaceous in composition, +with little vegetable matter, and bleached by the drainage from them of +water containing the products of vegetable decay. They are, in short, +loamy or clay soils, and must have been sufficiently above water to admit +of drainage. The absence of sulphurets, and the occurrence of carbonate +of iron in connection with them, prove that, when they existed as soils, +rain-water, and not sea-water, percolated them. (5) The coal and the +fossil forests present many evidences of subaërial conditions. Most of +the erect and prostrate trees had become hollow shells of bark before +they were finally embedded, and their wood had broken into cubical pieces +of mineral charcoal. Land-snails and galley-worms (_Xylobius_) crept into +them, and they became dens, or traps, for reptiles. Large quantities of +mineral charcoal occur on the surface of all the large beds of coal. None +of these appearances could have been produced by subaqueous action. (6) +Though the roots of the _Sigillaria_ bear more resemblance to the +rhizomes of certain aquatic plants; yet, structurally, they are +absolutely identical with the roots of Cycads, which the stems also +resemble. Further, the _Sigillarioe_ grew on the same soils which +supported Conifers, _Lepidodendra_, _Cordaites_, and Ferns-plants which +could not have grown in water. Again, with the exception perhaps of some +_Pinnularioe_, and _Asterophyllites_, there is a remarkable absence from +the coal measures of any form of properly aquatic vegetation. (7) The +occurrence of marine, or brackish-water animals, in the roofs of coal- +beds, or even in the coal itself, affords no evidence of subaqueous +accumulation, since the same thing occurs in the case of modern submarine +forests. For these and other reasons, some of which are more fully stated +in the papers already referred to, while I admit that the areas of coal +accumulation were frequently submerged, I must maintain that the true +coal is a subaërial accumulation by vegetable growth on soils, wet and +swampy it is true, but not submerged." + +I am almost disposed to doubt whether it is necessary to make the +concession of "wet and swampy"; otherwise, there is nothing that I know +of to be said against this excellent conspectus of the reasons for +believing in the subaërial origin of coal. + +But the coal accumulated upon the area covered by one of the great +forests of the carboniferous epoch would in course of time, have been +wasted away by the small, but constant, wear and tear of rain and streams +had the land which supported it remained at the same level, or been +gradually raised to a greater elevation. And, no doubt, as much coal as +now exists has been destroyed, after its formation, in this way. What are +now known as coal districts owe their importance to the fact that they +were areas of slow depression, during a greater or less portion of the +carboniferous epoch; and that, in virtue of this circumstance, Mother +Earth was enabled to cover up her vegetable treasures, and preserve them +from destruction. + +Wherever a coal-field now exists, there must formerly have been free +access for a great river, or for a shallow sea, bearing sediment in the +shape of sand and mud. When the coal-forest area became slowly depressed, +the waters must have spread over it, and have deposited their burden upon +the surface of the bed of coal, in the form of layers, which are now +converted into shale, or sandstone. Then followed a period of rest, in +which the superincumbent shallow waters became completely filled up, and +finally replaced, by fine mud, which settled down into a new under-clay, +and furnished the soil for a fresh forest growth. This flourished, and +heaped up its spores and wood into coal, until the stage of slow +depression recommenced. And, in some localities, as I have mentioned, the +process was repeated until the first of the alternating beds had sunk to +near three miles below its original level at the surface of the earth. + +In reflecting on the statement, thus briefly made, of the main facts +connected with the origin of the coal formed during the carboniferous +epoch, two or three considerations suggest themselves. + +In the first place, the great phantom of geological time rises before the +student of this, as of all other, fragments of the history of our earth-- +springing irrepressibly out of the facts, like the Djin from the jar +which the fishermen so incautiously opened; and like the Djin again, +being vaporous, shifting, and indefinable, but unmistakably gigantic. +However modest the bases of one's calculation may be, the minimum of time +assignable to the coal period remains something stupendous. + +Principal Dawson is the last person likely to be guilty of exaggeration +in this matter, and it will be well to consider what he has to say about +it:-- + +"The rate of accumulation of coal was very slow. The climate of the +period, in the northern temperate zone, was of such a character that the +true conifers show rings of growth, not larger, nor much less distinct, +than those of many of their modern congeners. The _Sigillarioe_ and +_Calamites_ were not, as often supposed, composed wholly, or even +principally, of lax and soft tissues, or necessarily short-lived. The +former had, it is true, a very thick inner bark; but their dense woody +axis, their thick and nearly imperishable outer bark, and their scanty +and rigid foliage, would indicate no very rapid growth or decay. In the +case of the _Sigillarioe_, the variations in the leaf-scars in different +parts of the trunk, the intercalation of new ridges at the surface +representing that of new woody wedges in the axis, the transverse marks +left by the stages of upward growth, all indicate that several years must +have been required for the growth of stems of moderate size. The enormous +roots of these trees, and the condition of the coal-swamps, must have +exempted them from the danger of being overthrown by violence. They +probably fell in successive generations from natural decay; and making +every allowance for other materials, we may safely assert that every foot +of thickness of pure bituminous coal implies the quiet growth and fall of +at least fifty generations of _Sigillarioe_, and therefore an undisturbed +condition of forest growth enduring through many centuries. Further, +there is evidence that an immense amount of loose parenchymatous tissue, +and even of wood, perished by decay, and we do not know to what extent +even the most durable tissues may have disappeared in this way; so that, +in many coal-seams, we may have only a very small part of the vegetable +matter produced." + +Undoubtedly the force of these reflections is not diminished when the +bituminous coal, as in Britain, consists of accumulated spores and spore- +cases, rather than of stems. But, suppose we adopt Principal Dawson's +assumption, that one foot of coal represents fifty generations of coal +plants; and, further, make the moderate supposition that each generation +of coal plants took ten years to come to maturity--then, each foot- +thickness of coal represents five hundred years. The superimposed beds of +coal in one coal-field may amount to a thickness of fifty or sixty feet, +and therefore the coal alone, in that field, represents 500 x 50 = 25,000 +years. But the actual coal is but an insignificant portion of the total +deposit, which, as has been seen, may amount to between two and three +miles of vertical thickness. Suppose it be 12,000 feet--which is 240 +times the thickness of the actual coal--is there any reason why we should +believe it may not have taken 240 times as long to form? I know of none. +But, in this case, the time which the coal-field represents would be +25,000 x 240 = 6,000,000 years. As affording a definite chronology, of +course such calculations as these are of no value; but they have much use +in fixing one's attention upon a possible minimum. A man may be puzzled +if he is asked how long Rome took a-building; but he is proverbially safe +if he affirms it not to have been built in a day; and our geological +calculations are all, at present, pretty much on that footing. + +A second consideration which the study of the coal brings prominently +before the mind of any one who is familiar with palaeontology is, that the +coal Flora, viewed in relation to the enormous period of time which it +lasted, and to the still vaster period which has elapsed since it +flourished, underwent little change while it endured, and in its peculiar +characters, differs strangely little from that which at present exist. + +The same species of plants are to be met with throughout the whole +thickness of a coal-field, and the youngest are not sensibly different +from the oldest. But more than this. Notwithstanding that the +carboniferous period is separated from us by more than the whole time +represented by the secondary and tertiary formations, the great types of +vegetation were as distinct then as now. The structure of the modern +club-moss furnishes a complete explanation of the fossil remains of the +_Lepidodendra_, and the fronds of some of the ancient ferns are hard to +distinguish from existing ones. At the same time, it must be remembered, +that there is nowhere in the world, at present, any _forest_ which bears +more than a rough analogy with a coal-forest. The types may remain, but +the details of their form, their relative proportions, their associates, +are all altered. And the tree-fern forest of Tasmania, or New Zealand, +gives one only a faint and remote image of the vegetation of the ancient +world. + +Once more, an invariably-recurring lesson of geological history, at +whatever point its study is taken up: the lesson of the almost infinite +slowness of the modification of living forms. The lines of the pedigrees +of living things break off almost before they begin to converge. + +Finally, yet another curious consideration. Let us suppose that one of +the stupid, salamander-like Labyrinthodonts, which pottered, with much +belly and little leg, like Falstaff in his old age, among the coal- +forests, could have had thinking power enough in his small brain to +reflect upon the showers of spores which kept on falling through years +and centuries, while perhaps not one in ten million fulfilled its +apparent purpose, and reproduced the organism which gave it birth: surely +he might have been excused for moralizing upon the thoughtless and wanton +extravagance which Nature displayed in her operations. + +But we have the advantage over our shovel-headed predecessor--or possibly +ancestor--and can perceive that a certain vein of thrift runs through +this apparent prodigality. Nature is never in a hurry, and seems to have +had always before her eyes the adage, "Keep a thing long enough, and you +will find a use for it." She has kept her beds of coal many millions of +years without being able to find much use for them; she has sent them +down beneath the sea, and the sea-beasts could make nothing of them; she +has raised them up into dry land, and laid the black veins bare, and +still, for ages and ages, there was no living thing on the face of the +earth that could see any sort of value in them; and it was only the other +day, so to speak, that she turned a new creature out of her workshop, who +by degrees acquired sufficient wits to make a fire, and then to discover +that the black rock would burn. + +I suppose that nineteen hundred years ago, when Julius Caesar was good +enough to deal with Britain as we have dealt with New Zealand, the +primaeval Briton, blue with cold and woad, may have known that the strange +black stone, of which he found lumps here and there in his wanderings, +would burn, and so help to warm his body and cook his food. Saxon, Dane, +and Norman swarmed into the land. The English people grew into a powerful +nation, and Nature still waited for a full return of the capital she had +invested in the ancient club-mosses. The eighteenth century arrived, and +with it James Watt. The brain of that man was the spore out of which was +developed the modern steam-engine, and all the prodigious trees and +branches of modern industry which have grown out of this. But coal is as +much an essential condition of this growth and development as carbonic +acid is for that of a club-moss. Wanting coal, we could not have smelted +the iron needed to make our engines, nor have worked our engines when we +had got them. But take away the engines, and the great towns of Yorkshire +and Lancashire vanish like a dream. Manufactures give place to +agriculture and pasture, and not ten men can live where now ten thousand +are amply supported. + +Thus, all this abundant wealth of money and of vivid life is Nature's +interest upon her investment in club-mosses, and the like, so long ago. +But what becomes of the coal which is burnt in yielding this interest? +Heat comes out of it, light comes out of it; and if we could gather +together all that goes up the chimney, and all that remains in the grate +of a thoroughly-burnt coal-fire, we should find ourselves in possession +of a quantity of carbonic acid, water, ammonia, and mineral matters, +exactly equal in weight to the coal. But these are the very matters with +which Nature supplied the club-mosses which made the coal She is paid +back principal and interest at the same time; and she straightway invests +the carbonic acid, the water, and the ammonia in new forms of life, +feeding with them the plants that now live. Thrifty Nature! Surely no +prodigal, but most notable of housekeepers! + + + +VI + + +ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS + +[1876] + +In the whole history of science there is nothing more remarkable than the +rapidity of the growth of biological knowledge within the last half- +century, and the extent of the modification which has thereby been +effected in some of the fundamental conceptions of the naturalist. + +In the second edition of the "Règne Animal," published in 1828, Cuvier +devotes a special section to the "Division of Organised Beings into +Animals and Vegetables," in which the question is treated with that +comprehensiveness of knowledge and clear critical judgment which +characterise his writings, and justify us in regarding them as +representative expressions of the most extensive, if not the profoundest, +knowledge of his time. He tells us that living beings have been +subdivided from the earliest times into _animated beings_, which possess +sense and motion, and _inanimated beings_, which are devoid of these +functions and simply vegetate. + +Although the roots of plants direct themselves towards moisture, and +their leaves towards air and light,--although the parts of some plants +exhibit oscillating movements without any perceptible cause, and the +leaves of others retract when touched,--yet none of these movements +justify the ascription to plants of perception or of will. From the +mobility of animals, Cuvier, with his characteristic partiality for +teleological reasoning, deduces the necessity of the existence in them of +an alimentary cavity, or reservoir of food, whence their nutrition may be +drawn by the vessels, which are a sort of internal roots; and, in the +presence of this alimentary cavity, he naturally sees the primary and the +most important distinction between animals and plants. + +Following out his teleological argument, Cuvier remarks that the +organisation of this cavity and its appurtenances must needs vary +according to the nature of the aliment, and the operations which it has +to undergo, before it can be converted into substances fitted for +absorption; while the atmosphere and the earth supply plants with juices +ready prepared, and which can be absorbed immediately. As the animal body +required to be independent of heat and of the atmosphere, there were no +means by which the motion of its fluids could be produced by internal +causes. Hence arose the second great distinctive character of animals, or +the circulatory system, which is less important than the digestive, since +it was unnecessary, and therefore is absent, in the more simple animals. + +Animals further needed muscles for locomotion and nerves for sensibility. +Hence, says Cuvier, it was necessary that the chemical composition of the +animal body should be more complicated than that of the plant; and it is +so, inasmuch as an additional substance, nitrogen, enters into it as an +essential element; while, in plants, nitrogen is only accidentally joined +with he three other fundamental constituents of organic beings--carbon, +hydrogen, and oxygen. Indeed, he afterwards affirms that nitrogen is +peculiar to animals; and herein he places the third distinction between +the animal and the plant. The soil and the atmosphere supply plants with +water, composed of hydrogen and oxygen; air, consisting of nitrogen and +oxygen; and carbonic acid, containing carbon and oxygen. They retain the +hydrogen and the carbon, exhale the superfluous oxygen, and absorb little +or no nitrogen. The essential character of vegetable life is the +exhalation of oxygen, which is effected through the agency of light. +Animals, on the contrary, derive their nourishment either directly or +indirectly from plants. They get rid of the superfluous hydrogen and +carbon, and accumulate nitrogen. The relations of plants and animals to +the atmosphere are therefore inverse. The plant withdraws water and +carbonic acid from the atmosphere, the animal contributes both to it. +Respiration--that is, the absorption of oxygen and the exhalation of +carbonic acid--is the specially animal function of animals, and +constitutes their fourth distinctive character. + +Thus wrote Cuvier in 1828. But, in the fourth and fifth decades of this +century, the greatest and most rapid revolution which biological science +has ever undergone was effected by the application of the modern +microscope to the investigation of organic structure; by the introduction +of exact and easily manageable methods of conducting the chemical +analysis of organic compounds; and finally, by the employment of +instruments of precision for the measurement of the physical forces which +are at work in the living economy. + +That the semi-fluid contents (which we now term protoplasm) of the cells +of certain plants, such as the _Charoe_ are in constant and regular +motion, was made out by Bonaventura Corti a century ago; but the fact, +important as it was, fell into oblivion, and had to be rediscovered by +Treviranus in 1807. Robert Brown noted the more complex motions of the +protoplasm in the cells of _Tradescantia_ in 1831; and now such movements +of the living substance of plants are well known to be some of the most +widely-prevalent phenomena of vegetable life. + +Agardh, and other of the botanists of Cuvier's generation, who occupied +themselves with the lower plants, had observed that, under particular +circumstances, the contents of the cells of certain water-weeds were set +free, and moved about with considerable velocity, and with all the +appearances of spontaneity, as locomotive bodies, which, from their +similarity to animals of simple organisation, were called "zoospores." +Even as late as 1845, however, a botanist of Schleiden's eminence dealt +very sceptically with these statements; and his scepticism was the more +justified, since Ehrenberg, in his elaborate and comprehensive work on +the _Infusoria_, had declared the greater number of what are now +recognised as locomotive plants to be animals. + +At the present day, innumerable plants and free plant cells are known to +pass the whole or part of their lives in an actively locomotive +condition, in no wise distinguishable from that of one of the simpler +animals; and, while in this condition, their movements are, to all +appearance, as spontaneous--as much the product of volition--as those of +such animals. + +Hence the teleological argument for Cuvier's first diagnostic character-- +the presence in animals of an alimentary cavity, or internal pocket, in +which they can carry about their nutriment--has broken down, so far, at +least, as his mode of stating it goes. And, with the advance of +microscopic anatomy, the universality of the fact itself among animals +has ceased to be predicable. Many animals of even complex structure, +which live parasitically within others, are wholly devoid of an +alimentary cavity. Their food is provided for them, not only ready +cooked, but ready digested, and the alimentary canal, become superfluous, +has disappeared. Again, the males of most Rotifers have no digestive +apparatus; as a German naturalist has remarked, they devote themselves +entirely to the "Minnedienst," and are to be reckoned among the few +realisations of the Byronic ideal of a lover. Finally, amidst the lowest +forms of animal life, the speck of gelatinous protoplasm, which +constitutes the whole body, has no permanent digestive cavity or mouth, +but takes in its food anywhere; and digests, so to speak, all over its +body. But although Cuvier's leading diagnosis of the animal from the +plant will not stand a strict test, it remains one of the most constant +of the distinctive characters of animals. And, if we substitute for the +possession of an alimentary cavity, the power of taking solid nutriment +into the body and there digesting it, the definition so changed will +cover all animals except certain parasites, and the few and exceptional +cases of non-parasitic animals which do not feed at all. On the other +hand, the definition thus amended will exclude all ordinary vegetable +organisms. + +Cuvier himself practically gives up his second distinctive mark when he +admits that it is wanting in the simpler animals. + +The third distinction is based on a completely erroneous conception of +the chemical differences and resemblances between the constituents of +animal and vegetable organisms, for which Cuvier is not responsible, as +it was current among contemporary chemists. It is now established that +nitrogen is as essential a constituent of vegetable as of animal living +matter; and that the latter is, chemically speaking, just as complicated +as the former. Starchy substances, cellulose and sugar, once supposed to +be exclusively confined to plants, are now known to be regular and normal +products of animals. Amylaceous and saccharine substances are largely +manufactured, even by the highest animals; cellulose is widespread as a +constituent of the skeletons of the lower animals; and it is probable +that amyloid substances are universally present in the animal organism, +though not in the precise form of starch. + +Moreover, although it remains true that there is an inverse relation +between the green plant in sunshine and the animal, in so far as, under +these circumstances, the green plant decomposes carbonic acid and exhales +oxygen, while the animal absorbs oxygen and exhales carbonic acid; yet, +the exact researches of the modern chemical investigators of the +physiological processes of plants have clearly demonstrated the fallacy +of attempting to draw any general distinction between animals and +vegetables on this ground. In fact, the difference vanishes with the +sunshine, even in the case of the green plant; which, in the dark, +absorbs oxygen and gives out carbonic acid like any animal.[1] On the +other hand, those plants, such as the fungi, which contain no chlorophyll +and are not green, are always, so far as respiration is concerned, in the +exact position of animals. They absorb oxygen and give out carbonic acid. + +[Footnote 1: There is every reason to believe that living plants, like +living animals, always respire, and, in respiring, absorb oxygen and give +off carbonic acid; but, that in green plants exposed to daylight or to +the electric light, the quantity of oxygen evolved in consequence of the +decomposition of carbonic acid by a special apparatus which green plants +possess exceeds that absorbed in the concurrent respiratory process.] + +Thus, by the progress of knowledge, Cuvier's fourth distinction between +the animal and the plant has been as completely invalidated as the third +and second; and even the first can be retained only in a modified form +and subject to exceptions. + +But has the advance of biology simply tended to break down old +distinctions, without establishing new ones? + +With a qualification, to be considered presently, the answer to this +question is undoubtedly in the affirmative. The famous researches of +Schwann and Schleiden in 1837 and the following years, founded the modern +science of histology, or that branch of anatomy which deals with the +ultimate visible structure of organisms, as revealed by the microscope; +and, from that day to this, the rapid improvement of methods of +investigation, and the energy of a host of accurate observers, have given +greater and greater breadth and firmness to Schwann's great +generalisation, that a fundamental unity of structure obtains in animals +and plants; and that, however diverse may be the fabrics, or _tissues_, +of which their bodies are composed, all these varied structures result +from the metamorphosis of morphological units (termed _cells_, in a more +general sense than that in which the word "cells" was at first employed), +which are not only similar in animals and in plants respectively, but +present a close resemblance, when those of animals and those of plants +are compared together. + +The contractility which is the fundamental condition of locomotion, has +not only been discovered to exist far more widely among plants than was +formerly imagined; but, in plants, the act of contraction has been found +to be accompanied, as Dr. Burdon Sanderson's interesting investigations +have shown, by a disturbance of the electrical state of the contractile +substance, comparable to that which was found by Du Bois Reymond to be a +concomitant of the activity of ordinary muscle in animals. + +Again, I know of no test by which the reaction of the leaves of the +Sundew and of other plants to stimuli, so fully and carefully studied by +Mr. Darwin, can be distinguished from those acts of contraction following +upon stimuli, which are called "reflex" in animals. + +On each lobe of the bilobed leaf of Venus's fly-trap (_Dionoea +muscipula_) are three delicate filaments which stand out at right angle +from the surface of the leaf. Touch one of them with the end of a fine +human hair and the lobes of the leaf instantly close together[2] in +virtue of an act of contraction of part of their substance, just as the +body of a snail contracts into its shell when one of its "horns" is +irritated. + +[Footnote 2: Darwin, _Insectivorous Plants_, p. 289.] + +The reflex action of the snail is the result of the presence of a nervous +system in the animal. A molecular change takes place in the nerve of the +tentacle, is propagated to the muscles by which the body is retracted, +and causing them to contract, the act of retraction is brought about. Of +course the similarity of the acts does not necessarily involve the +conclusion that the mechanism by which they are effected is the same; but +it suggests a suspicion of their identity which needs careful testing. + +The results of recent inquiries into the structure of the nervous system +of animals converge towards the conclusion that the nerve fibres, which +we have hitherto regarded as ultimate elements of nervous tissue, are not +such, but are simply the visible aggregations of vastly more attenuated +filaments, the diameter of which dwindles down to the limits of our +present microscopic vision, greatly as these have been extended by modern +improvements of the microscope; and that a nerve is, in its essence, +nothing but a linear tract of specially modified protoplasm between two +points of an organism--one of which is able to affect the other by means +of the communication so established. Hence, it is conceivable that even +the simplest living being may possess a nervous system. And the question +whether plants are provided with a nervous system or not, thus acquires a +new aspect, and presents the histologist and physiologist with a problem +of extreme difficulty, which must be attacked from a new point of view +and by the aid of methods which have yet to be invented. + +Thus it must be admitted that plants may be contractile and locomotive; +that, while locomotive, their movements may have as much appearance of +spontaneity as those of the lowest animals; and that many exhibit +actions, comparable to those which are brought about by the agency of a +nervous system in animals. And it must be allowed to be possible that +further research may reveal the existence of something comparable to a +nervous system in plants. So that I know not where we can hope to find +any absolute distinction between animals and plants, unless we return to +their mode of nutrition, and inquire whether certain differences of a +more occult character than those imagined to exist by Cuvier, and which +certainly hold good for the vast majority of animals and plants, are of +universal application. + +A bean may be supplied with water in which salts of ammonia and certain +other mineral salts are dissolved in due proportion; with atmospheric air +containing its ordinary minute dose of carbonic acid; and with nothing +else but sunlight and heat. Under these circumstances, unnatural as they +are, with proper management, the bean will thrust forth its radicle and +its plumule; the former will grow down into roots, the latter grow up +into the stem and leaves of a vigorous bean-plant; and this plant will, +in due time, flower and produce its crop of beans, just as if it were +grown in the garden or in the field. + +The weight of the nitrogenous protein compounds, of the oily, starchy, +saccharine and woody substances contained in the full-grown plant and its +seeds, will be vastly greater than the weight of the same substances +contained in the bean from which it sprang. But nothing has been supplied +to the bean save water, carbonic acid, ammonia, potash, lime, iron, and +the like, in combination with phosphoric, sulphuric, and other acids. +Neither protein, nor fat, nor starch, nor sugar, nor any substance in the +slightest degree resembling them, has formed part of the food of the +bean. But the weights of the carbon, hydrogen, oxygen, nitrogen, +phosphorus, sulphur, and other elementary bodies contained in the bean- +plant, and in the seeds which it produces, are exactly equivalent to the +weights of the same elements which have disappeared from the materials +supplied to the bean during its growth. Whence it follows that the bean +has taken in only the raw materials of its fabric, and has manufactured +them into bean-stuffs. + +The bean has been able to perform this great chemical feat by the help of +its green colouring matter, or chlorophyll; for it is only the green +parts of the plant which, under the influence of sunlight, have the +marvellous power of decomposing carbonic acid, setting free the oxygen +and laying hold of the carbon which it contains. In fact, the bean +obtains two of the absolutely indispensable elements of its substance +from two distinct sources; the watery solution, in which its roots are +plunged, contains nitrogen but no carbon; the air, to which the leaves +are exposed, contains carbon, but its nitrogen is in the state of a free +gas, in which condition the bean can make no use of it;[3] and the +chlorophyll[4] is the apparatus by which the carbon is extracted from the +atmospheric carbonic acid--the leaves being the chief laboratories in +which this operation is effected. + +[Footnote 3: I purposely assume that the air with which the bean is +supplied in the case stated contains no ammoniacal salts.] + +[Footnote 4: The recent researches of Pringsheim have raised a host of +questions as to the exact share taken by chlorophyll in the chemical +operations which are effected by the green parts of plants. It may be +that the chlorophyll is only a constant concomitant of the actual +deoxidising apparatus.] + +The great majority of conspicuous plants are, as everybody knows, green; +and this arises from the abundance of their chlorophyll. The few which +contain no chlorophyll and are colourless, are unable to extract the +carbon which they require from atmospheric carbonic acid, and lead a +parasitic existence upon other plants; but it by no means follows, often +as the statement has been repeated, that the manufacturing power of +plants depends on their chlorophyll, and its interaction with the rays of +the sun. On the contrary, it is easily demonstrated, as Pasteur first +proved, that the lowest fungi, devoid of chlorophyll, or of any +substitute for it, as they are, nevertheless possess the characteristic +manufacturing powers of plants in a very high degree. Only it is +necessary that they should be supplied with a different kind of raw +material; as they cannot extract carbon from carbonic acid, they must be +furnished with something else that contains carbon. Tartaric acid is such +a substance; and if a single spore of the commonest and most troublesome +of moulds--_Penicillium_--be sown in a saucerful of water, in which +tartrate of ammonia, with a small percentage of phosphates and sulphates +is contained, and kept warm, whether in the dark or exposed to light, it +will, in a short time, give rise to a thick crust of mould, which +contains many million times the weight of the original spore, in protein +compounds and cellulose. Thus we have a very wide basis of fact for the +generalisation that plants are essentially characterised by their +manufacturing capacity--by their power of working up mere mineral matters +into complex organic compounds. + +Contrariwise, there is a no less wide foundation for the generalisation +that animals, as Cuvier puts it, depend directly or indirectly upon +plants for the materials of their bodies; that is, either they are +herbivorous, or they eat other animals which are herbivorous. + +But for what constituents of their bodies are animals thus dependent upon +plants? Certainly not for their horny matter; nor for chondrin, the +proximate chemical element of cartilage; nor for gelatine; nor for +syntonin, the constituent of muscle; nor for their nervous or biliary +substances; nor for their amyloid matters; nor, necessarily, for their +fats. + +It can be experimentally demonstrated that animals can make these for +themselves. But that which they cannot make, but must, in all known +cases, obtain directly or indirectly from plants, is the peculiar +nitrogenous matter, protein. Thus the plant is the ideal _prolétaire_ of +the living world, the worker who produces; the animal, the ideal +aristocrat, who mostly occupies himself in consuming, after the manner of +that noble representative of the line of Zähdarm, whose epitaph is +written in "Sartor Resartus." + +Here is our last hope of finding a sharp line of demarcation between +plants and animals; for, as I have already hinted, there is a border +territory between the two kingdoms, a sort of no-man's-land, the +inhabitants of which certainly cannot be discriminated and brought to +their proper allegiance in any other way. + +Some months ago, Professor Tyndall asked me to examine a drop of infusion +of hay, placed under an excellent and powerful microscope, and to tell +him what I thought some organisms visible in it were. I looked and +observed, in the first place, multitudes of _Bacteria_ moving about with +their ordinary intermittent spasmodic wriggles. As to the vegetable +nature of these there is now no doubt. Not only does the close +resemblance of the _Bacteria_ to unquestionable plants, such as the +_Oscillatorioe_ and the lower forms of _Fungi_, justify this conclusion, +but the manufacturing test settles the question at once. It is only +needful to add a minute drop of fluid containing _Bacteria_, to water in +which tartrate, phosphate, and sulphate of ammonia are dissolved; and, in +a very short space of time, the clear fluid becomes milky by reason of +their prodigious multiplication, which, of course, implies the +manufacture of living Bacterium-stuff out of these merely saline matters. + +But other active organisms, very much larger than the _Bacteria_, +attaining in fact the comparatively gigantic dimensions of 1/3000 of an +inch or more, incessantly crossed the field of view. Each of these had a +body shaped like a pear, the small end being slightly incurved and +produced into a long curved filament, or _cilium_, of extreme tenuity. +Behind this, from the concave side of the incurvation, proceeded another +long cilium, so delicate as to be discernible only by the use of the +highest powers and careful management of the light. In the centre of the +pear-shaped body a clear round space could occasionally be discerned, but +not always; and careful watching showed that this clear vacuity appeared +gradually, and then shut up and disappeared suddenly, at regular +intervals. Such a structure is of common occurrence among the lowest +plants and animals, and is known as a _contractile vacuole_. + +The little creature thus described sometimes propelled itself with great +activity, with a curious rolling motion, by the lashing of the front +cilium, while the second cilium trailed behind; sometimes it anchored +itself by the hinder cilium and was spun round by the working of the +other, its motions resembling those of an anchor buoy in a heavy sea. +Sometimes, when two were in full career towards one another, each would +appear dexterously to get out of the other's way; sometimes a crowd would +assemble and jostle one another, with as much semblance of individual +effort as a spectator on the Grands Mulets might observe with a telescope +among the specks representing men in the valley of Chamounix. + +The spectacle, though always surprising, was not new to me. So my reply +to the question put to me was, that these organisms were what biologists +call _Monads_, and though they might be animals, it was also possible +that they might, like the _Bacteria_, be plants. My friend received my +verdict with an expression which showed a sad want of respect for +authority. He would as soon believe that a sheep was a plant. Naturally +piqued by this want of faith, I have thought a good deal over the matter; +and, as I still rest in the lame conclusion I originally expressed, and +must even now confess that I cannot certainly say whether this creature +is an animal or a plant, I think it may be well to state the grounds of +my hesitation at length. But, in the first place, in order that I may +conveniently distinguish this "Monad" from the multitude of other things +which go by the same designation, I must give it a name of its own. I +think (though, for reasons which need not be stated at present, I am not +quite sure) that it is identical with the species _Monas lens_ as defined +by the eminent French microscopist Dujardin, though his magnifying power +was probably insufficient to enable him to see that it is curiously like +a much larger form of monad which he has named _Heteromita_. I shall, +therefore, call it not _Monas_, but _Heteromita lens_. + +I have been unable to devote to my _Heteromita_ the prolonged study +needful to work out its whole history, which would involve weeks, or it +may be months, of unremitting attention. But I the less regret this +circumstance, as some remarkable observations recently published by +Messrs. Dallinger and Drysdale[5] on certain Monads, relate, in part, to +a form so similar to my _Heteromita lens_, that the history of the one +may be used to illustrate that of the other. These most patient and +painstaking observers, who employed the highest attainable powers of the +microscope and, relieving one another, kept watch day and night over the +same individual monads, have been enabled to trace out the whole history +of their _Heteromita_; which they found in infusions of the heads of +fishes of the Cod tribe. + +[Footnote 5: "Researches in the Life-history of a Cercomonad: a Lesson in +Biogenesis"; and "Further Researches in the Life-history of the Monads," +--_Monthly Microscopical Journal_, 1873.] + +Of the four monads described and figured by these investigators, one, as +I have said, very closely resembles _Heteromita lens_ in every +particular, except that it has a separately distinguishable central +particle or "nucleus," which is not certainly to be made out in +_Heteromita lens_; and that nothing is said by Messrs. Dallinger and +Drysdale of the existence of a contractile vacuole in this monad, though +they describe it in another. + +Their _Heteromita_, however, multiplied rapidly by fission. Sometimes a +transverse constriction appeared; the hinder half developed a new cilium, +and the hinder cilium gradually split from its base to its free end, +until it was divided into two; a process which, considering the fact that +this fine filament cannot be much more than 1/100000 of an inch in +diameter, is wonderful enough. The constriction of the body extended +inwards until the two portions were united by a narrow isthmus; finally, +they separated and each swam away by itself, a complete _Heteromita_, +provided with its two cilia. Sometimes the constriction took a +longitudinal direction, with the same ultimate result. In each case the +process occupied not more than six or seven minutes. At this rate, a +single _Heteromita_ would give rise to a thousand like itself in the +course of an hour, to about a million in two hours, and to a number +greater than the generally assumed number of human beings now living in +the world in three hours; or, if we give each _Heteromita_ an hour's +enjoyment of individual existence, the same result will be obtained in +about a day. The apparent suddenness of the appearance of multitudes of +such organisms as these in any nutritive fluid to which one obtains +access is thus easily explained. + +During these processes of multiplication by fission, the _Heteromita_ +remains active; but sometimes another mode of fission occurs. The body +becomes rounded and quiescent, or nearly so; and, while in this resting +state, divides into two portions, each of which is rapidly converted into +an active _Heteromita_. + +A still more remarkable phenomenon is that kind of multiplication which +is preceded by the union of two monads, by a process which is termed +_conjugation_. Two active _Heteromitoe_ become applied to one another, +and then slowly and gradually coalesce into one body. The two nuclei run +into one; and the mass resulting from the conjugation of the two +_Heteromitoe_, thus fused together, has a triangular form. The two pairs +of cilia are to be seen, for some time, at two of the angles, which +answer to the small ends of the conjoined monads; but they ultimately +vanish, and the twin organism, in which all visible traces of +organisation have disappeared, falls into a state of rest. Sudden wave- +like movements of its substance next occur; and, in a short time, the +apices of the triangular mass burst, and give exit to a dense yellowish, +glairy fluid, filled with minute granules. This process, which, it will +be observed, involves the actual confluence and mixture of the substance +of two distinct organisms, is effected in the space of about two hours. + +The authors whom I quote say that they "cannot express" the excessive +minuteness of the granules in question, and they estimate their diameter +at less than 1/200000 of an inch. Under the highest powers of the +microscope, at present applicable, such specks are hardly discernible. +Nevertheless, particles of this size are massive when compared to +physical molecules; whence there is no reason to doubt that each, small +as it is, may have a molecular structure sufficiently complex to give +rise to the phenomena of life. And, as a matter of fact, by patient +watching of the place at which these infinitesimal living particles were +discharged, our observers assured themselves of their growth and +development into new monads. In about four hours from their being set +free, they had attained a sixth of the length of the parent, with the +characteristic cilia, though at first they were quite motionless; and, in +four hours more, they had attained the dimensions and exhibited all the +activity of the adult. These inconceivably minute particles are therefore +the germs of the _Heteromita_; and from the dimensions of these germs it +is easily shown that the body formed by conjugation may, at a low +estimate, have given exit to thirty thousand of them; a result of a +matrimonial process whereby the contracting parties, without a metaphor, +"become one flesh," enough to make a Malthusian despair of the future of +the Universe. + +I am not aware that the investigators from whom I have borrowed this +history have endeavoured to ascertain whether their monads take solid +nutriment or not; so that though they help us very much to fill up the +blanks in the history of my _Heteromita_, their observations throw no +light on the problem we are trying to solve--Is it an animal or is it a +plant? + +Undoubtedly it is possible to bring forward very strong arguments in +favour of regarding _Heteromita_ as a plant. + +For example, there is a Fungus, an obscure and almost microscopic mould, +termed _Peronospora infestans_. Like many other Fungi, the _Peronosporoe_ +are parasitic upon other plants; and this particular _Peronospora_ +happens to have attained much notoriety and political importance, in a +way not without a parallel in the career of notorious politicians, +namely, by reason of the frightful mischief it has done to mankind. For +it is this _Fungus_ which is the cause of the potato disease; and, +therefore, _Peronospora infestans_ (doubtless of exclusively Saxon +origin, though not accurately known to be so) brought about the Irish +famine. The plants afflicted with the malady are found to be infested by +a mould, consisting of fine tubular filaments, termed _hyphoe_, which +burrow through the substance of the potato plant, and appropriate to +themselves the substance of their host; while, at the same time, directly +or indirectly, they set up chemical changes by which even its woody +framework becomes blackened, sodden, and withered. + +In structure, however, the _Peronospora_ is as much a mould as the common +_Penicillium_; and just as the _Penicillium_ multiplies by the breaking +up of its hyphoe into separate rounded bodies, the spores; so, in the +_Peronospora_, certain of the hyphoe grow out into the air through the +interstices of the superficial cells of the potato plant, and develop +spores. Each of these hyphoe usually gives off several branches. The ends +of the branches dilate and become closed sacs, which eventually drop off +as spores. The spores falling on some part of the same potato plant, or +carried by the wind to another, may at once germinate, throwing out +tubular prolongations which become hyphoe, and burrow into the substance +of the plant attacked. But, more commonly, the contents of the spore +divide into six or eight separate portions. The coat of the spore gives +way, and each portion then emerges as an independent organism, which has +the shape of a bean, rather narrower at one end than the other, convex on +one side, and depressed or concave on the opposite. From the depression, +two long and delicate cilia proceed, one shorter than the other, and +directed forwards. Close to the origin of these cilia, in the substance +of the body, is a regularly pulsating, contractile vacuole. The shorter +cilium vibrates actively, and effects the locomotion of the organism, +while the other trails behind; the whole body rolling on its axis with +its pointed end forwards. + +The eminent botanist, De Bary, who was not thinking of our problem, tells +us, in describing the movements of these "Zoospores," that, as they swim +about, "Foreign bodies are carefully avoided, and the whole movement has +a deceptive likeness to the voluntary changes of place which are observed +in microscopic animals." + +After swarming about in this way in the moisture on the surface of a leaf +or stem (which, film though it may be, is an ocean to such a fish) for +half an hour, more or less, the movement of the zoospore becomes slower, +and is limited to a slow turning upon its axis, without change of place. +It then becomes quite quiet, the cilia disappear, it assumes a spherical +form, and surrounds itself with a distinct, though delicate, membranous +coat. A protuberance then grows out from one side of the sphere, and +rapidly increasing in length, assumes the character of a hypha. The +latter penetrates into the substance of the potato plant, either by +entering a stomate, or by boring through the wall of an epidermic cell, +and ramifies, as a mycelium, in the substance of the plant, destroying +the tissues with which it comes in contact. As these processes of +multiplication take place very rapidly, millions of spores are soon set +free from a single infested plant; and, from their minuteness, they are +readily transported by the gentlest breeze. Since, again, the zoospores +set free from each spore, in virtue of their powers of locomotion, +swiftly disperse themselves over the surface, it is no wonder that the +infection, once started, soon spreads from field to field, and extends +its ravages over a whole country. + +However, it does not enter into my present plan to treat of the potato +disease, instructively as its history bears upon that of other epidemics; +and I have selected the case of the _Peroganspora_ simply because it +affords an example of an organism, which, in one stage of its existence, +is truly a "Monad," indistinguishable by any important character from our +_Heteromita_, and extraordinarily like it in some respects. And yet this +"Monad" can be traced, step by step, through the series of metamorphoses +which I have described, until it assumes the features of an organism, +which is as much a plant as is an oak or an elm. + +Moreover, it would be possible to pursue the analogy farther. Under +certain circumstances, a process of conjugation takes place in the +_Peronospora_. Two separate portions of its protoplasm become fused +together, surround themselves with a thick coat and give rise to a sort +of vegetable egg called an _oospore_. After a period of rest, the +contents of the oospore break up into a number of zoospores like those +already described, each of which, after a period of activity, germinates +in the ordinary way. This process obviously corresponds with the +conjugation and subsequent setting free of germs in the _Heteromita_. + +But it may be said that the _Peronospora_ is, after all, a questionable +sort of plant; that it seems to be wanting in the manufacturing power, +selected as the main distinctive character of vegetable life; or, at any +rate, that there is no proof that it does not get its protein matter +ready made from the potato plant. + +Let us, therefore, take a case which is not open to these objections. + +There are some small plants known to botanists as members of the genus +_Colcochaete_, which, without being truly parasitic, grow upon certain +water-weeds, as lichens grow upon trees. The little plant has the form of +an elegant green star, the branching arms of which are divided into +cells. Its greenness is due to its chlorophyll, and it undoubtedly has +the manufacturing power in full degree, decomposing carbonic acid and +setting oxygen free, under the influence of sunlight. But the +protoplasmic contents of some of the cells of which the plant is made up +occasionally divide, by a method similar to that which effects the +division of the contents of the _Peronospora_ spore; and the severed +portions are then set free as active monad-like zoospores. Each is oval +and is provided at one extremity with two long active cilia. Propelled by +these, it swims about for a longer or shorter time, but at length comes +to a state of rest and gradually grows into a _Coleochaete_. Moreover, as +in the _Peronospora_, conjugation may take place and result in an +oospore; the contents of which divide and are set free as monadiform +germs. + +If the whole history of the zoospores of _Peronospora_ and of +_Coleochaete_ were unknown, they would undoubtedly be classed among +"Monads" with the same right as _Heteromita_; why then may not +_Heteromita_ be a plant, even though the cycle of forms through which it +passes shows no terms quite so complex as those which occur in +_Peronospora_ and _Coleochaete_? And, in fact, there are some green +organisms, in every respect characteristically plants, such as +_Chlamydomonas_, and the common _Volvox_, or so-called "Globe +animalcule," which run through a cycle of forms of just the same simple +character as those of _Heteromita_. + +The name of _Chlamydomonas_ is applied to certain microscopic green +bodies, each of which consists of a protoplasmic central substance +invested by a structureless sac. The latter contains cellulose, as in +ordinary plants; and the chlorophyll which gives the green colour enables +the _Chlamydomonas_ to decompose carbonic acid and fix carbon as they do. +Two long cilia protrude through the cell-wall, and effect the rapid +locomotion of this "monad," which, in all respects except its mobility, +is characteristically a plant. Under ordinary circumstances, the +_Chlamydomonas_ multiplies by simple fission, each splitting into two or +into four parts, which separate and become independent organisms. +Sometimes, however, the _Chlamydomonas_ divides into eight parts, each of +which is provided with four instead of two cilia. These "zoospores" +conjugate in pairs, and give rise to quiescent bodies, which multiply by +division, find eventually pass into the active state. + +Thus, so far as outward form and the general character of the cycle of +modifications, through which the organism passes in the course of its +life, are concerned, the resemblance between _Chlamydomonas_ and +_Heteromita_ is of the closest description. And on the face of the matter +there is no ground for refusing to admit that _Heteromita_ may be related +to _Chlamydomonas_, as the colourless fungus is to the green alga. +_Volvox_ may be compared to a hollow sphere, the wall of which is made up +of coherent Chlamydomonads; and which progresses with a rotating motion +effected by the paddling of the multitudinous pairs of cilia which +project from its surface. Each _Volvox_-monad, moreover, possesses a red +pigment spot, like the simplest form of eye known among animals. The +methods of fissive multiplication and of conjugation observed in the +monads of this locomotive globe are essentially similar to those observed +in _Chlamydomonas_; and, though a hard battle has been fought over it, +_Volvox_ is now finally surrendered to the Botanists. + +Thus there is really no reason why _Heteromita_ may not be a plant; and +this conclusion would be very satisfactory, if it were not equally easy +to show that there is really no reason why it should not be an animal. +For there are numerous organisms presenting the closest resemblance to +_Heteromita_, and, like it, grouped under the general name of "Monads," +which, nevertheless, can be observed to take in solid nutriment, and +which, therefore, have a virtual, if not an actual, mouth and digestive +cavity, and thus come under Cuvier's definition of an animal. Numerous +forms of such animals have been described by Ehrenberg, Dujardin, H. +James Clark, and other writers on the _Infusoria_. Indeed, in another +infusion of hay in which my _Heteromita lens_ occurred, there were +innumerable such infusorial animalcules belonging to the well-known +species _Colpoda cucullus_.[6] + +[Footnote 6: Excellently described by Stein, almost all of whose +statements I have verified.] + +Full-sized specimens of this animalcule attain a length of between 1/300 +or 1/400 of an inch, so that it may have ten times the length and a +thousand times the mass of a _Heteromita_. In shape, it is not altogether +unlike _Heteromita_. The small end, however, is not produced into one +long cilium, but the general surface of the body is covered with small +actively vibrating ciliary organs, which are only longest at the small +end. At the point which answers to that from which the two cilia arise in +_Heteromita_, there is a conical depression, the mouth; and, in young +specimens, a tapering filament, which reminds one of the posterior cilium +of _Heteromita_, projects from this region. + +The body consists of a soft granular protoplasmic substance, the middle +of which is occupied by a large oval mass called the "nucleus"; while, at +its hinder end, is a "contractile vacuole," conspicuous by its regular +rhythmic appearances and disappearances. Obviously, although the +_Colpoda_ is not a monad, it differs from one only in subordinate +details. Moreover, under certain conditions, it becomes quiescent, +incloses itself in a delicate case or _cyst_, and then divides into two, +four, or more portions, which are eventually set free and swim about as +active _Colpodoe_. + +But this creature is an unmistakable animal, and full-sized _Colpodoe_ +may be fed as easily as one feeds chickens. It is only needful to diffuse +very finely ground carmine through the water in which they live, and, in +a very short time, the bodies of the _Colpodoe_ are stuffed with the +deeply-coloured granules of the pigment. + +And if this were not sufficient evidence of the animality of _Colpoda_, +there comes the fact that it is even more similar to another well-known +animalcule, _Paramoecium_, than it is to a monad. But _Paramoecium_ is so +huge a creature compared with those hitherto discussed--it reaches 1/120 +of an inch or more in length--that there is no difficulty in making out +its organisation in detail; and in proving that it is not only an animal, +but that it is an animal which possesses a somewhat complicated +organisation. For example, the surface layer of its body is different in +structure from the deeper parts. There are two contractile vacuoles, from +each of which radiates a system of vessel-like canals; and not only is +there a conical depression continuous with a tube, which serve as mouth +and gullet, but the food ingested takes a definite course, and refuse is +rejected from a definite region. Nothing is easier than to feed these +animals, and to watch the particles of indigo or carmine accumulate at +the lower end of the gullet. From this they gradually project, surrounded +by a ball of water, which at length passes with a jerk, oddly simulating +a gulp, into the pulpy central substance of the body, there to circulate +up one side and down the other, until its contents are digested and +assimilated. Nevertheless, this complex animal multiplies by division, as +the monad does, and, like the monad, undergoes conjugation. It stands in +the same relation to _Heteromita_ on the animal side, as _Coleochaete_ +does on the plant side. Start from either, and such an insensible series +of gradations leads to the monad that it is impossible to say at any +stage of the progress where the line between the animal and the plant +must be drawn. + +There is reason to think that certain organisms which pass through a +monad stage of existence, such as the _Myxomycetes_, are, at one time of +their lives, dependent upon external sources for their protein matter, or +are animals; and, at another period, manufacture it, or are plants. And +seeing that the whole progress of modern investigation is in favour of +the doctrine of continuity, it is a fair and probable speculation--though +only a speculation--that, as there are some plants which can manufacture +protein out of such apparently intractable mineral matters as carbonic +acid, water, nitrate of ammonia, metallic and earthy salts; while others +need to be supplied with their carbon and nitrogen in the somewhat less +raw form of tartrate of ammonia and allied compounds; so there may be yet +others, as is possibly the case with the true parasitic plants, which can +only manage to put together materials still better prepared--still more +nearly approximated to protein--until we arrive at such organisms as the +_Psorospermioe_ and the _Panhistophyton_, which are as much animal as +vegetable in structure, but are animal in their dependence on other +organisms for their food. + +The singular circumstance observed by Meyer, that the _Torula_ of yeast, +though an indubitable plant, still flourishes most vigorously when +supplied with the complex nitrogenous substance, pepsin; the probability +that the _Peronospora_ is nourished directly by the protoplasm of the +potato-plant; and the wonderful facts which have recently been brought to +light respecting insectivorous plants, all favour this view; and tend to +the conclusion that the difference between animal and plant is one of +degree rather than of kind, and that the problem whether, in a given +case, an organism is an animal or a plant, may be essentially insoluble. + + + +VII + + +A LOBSTER; OR, THE STUDY OF ZOOLOGY + +[1861] + +Natural history is the name familiarly applied to the study of the +properties of such natural bodies as minerals, plants, and animals; the +sciences which embody the knowledge man has acquired upon these subjects +are commonly termed Natural Sciences, in contradistinction to other so- +called "physical" sciences; and those who devote themselves especially to +the pursuit of such sciences have been and are commonly termed +"Naturalists." + +Linnaeus was a naturalist in this wide sense, and his "Systema Naturae" was +a work upon natural history, in the broadest acceptation of the term; in +it, that great methodising spirit embodied all that was known in his time +of the distinctive characters of minerals, animals, and plants. But the +enormous stimulus which Linnaeus gave to the investigation of nature soon +rendered it impossible that any one man should write another "Systema +Naturae," and extremely difficult for any one to become even a naturalist +such as Linnaeus was. + +Great as have been the advances made by all the three branches of +science, of old included under the title of natural history, there can be +no doubt that zoology and botany have grown in an enormously greater +ratio than mineralogy; and hence, as I suppose, the name of "natural +history" has gradually become more and more definitely attached to these +prominent divisions of the subject, and by "naturalist" people have meant +more and more distinctly to imply a student of the structure and function +of living beings. + +However this may be, it is certain that the advance of knowledge has +gradually widened the distance between mineralogy and its old associates, +while it has drawn zoology and botany closer together; so that of late +years it has been found convenient (and indeed necessary) to associate +the sciences which deal with vitality and all its phenomena under the +common head of "biology"; and the biologists have come to repudiate any +blood-relationship with their foster-brothers, the mineralogists. + +Certain broad laws have a general application throughout both the animal +and the vegetable worlds, but the ground common to these kingdoms of +nature is not of very wide extent, and the multiplicity of details is so +great, that the student of living beings finds himself obliged to devote +his attention exclusively either to the one or the other. If he elects to +study plants, under any aspect, we know at once what to call him. He is a +botanist, and his science is botany. But if the investigation of animal +life be his choice, the name generally applied to him will vary according +to the kind of animals he studies, or the particular phenomena of animal +life to which he confines his attention. If the study of man is his +object, he is called an anatomist, or a physiologist, or an ethnologist; +but if he dissects animals, or examines into the mode in which their +functions are performed, he is a comparative anatomist or comparative +physiologist. If he turns his attention to fossil animals, he is a +palaeontologist. If his mind is more particularly directed to the specific +description, discrimination, classification, and distribution of animals, +he is termed a zoologist. + +For the purpose of the present discourse, however, I shall recognise none +of these titles save the last, which I shall employ as the equivalent of +botanist, and I shall use the term zoology is denoting the whole doctrine +of animal life, in contradistinction to botany, which signifies the whole +doctrine of vegetable life. + +Employed in this sense, zoology, like botany, is divisible into three +great but subordinate sciences, morphology, physiology, and distribution, +each of which may, to a very great extent, be studied independently of +the other. + +Zoological morphology is the doctrine of animal form or structure. +Anatomy is one of its branches; development is another; while +classification is the expression of the relations which different animals +bear to one another, in respect of their anatomy and their development. + +Zoological distribution is the study of animals in relation to the +terrestrial conditions which obtain now, or have obtained at any previous +epoch of the earth's history. + +Zoological physiology, lastly, is the doctrine of the functions or +actions of animals. It regards animal bodies as machines impelled by +certain forces, and performing an amount of work which can be expressed +in terms of the ordinary forces of nature. The final object of physiology +is to deduce the facts of morphology, on the one hand, and those of +distribution on the other, from the laws of the molecular forces of +matter. + +Such is the scope of zoology. But if I were to content myself with the +enunciation of these dry definitions, I should ill exemplify that method +of teaching this branch of physical science, which it is my chief +business to-night to recommend. Let us turn away then from abstract +definitions. Let us take some concrete living thing, some animal, the +commoner the better, and let us see how the application of common sense +and common logic to the obvious facts it presents, inevitably leads us +into all these branches of zoological science. + +I have before me a lobster. When I examine it, what appears to be the +most striking character it presents? Why, I observe that this part which +we call the tail of the lobster, is made up of six distinct hard rings +and a seventh terminal piece. If I separate one of the middle rings, say +the third, I find it carries upon its under surface a pair of limbs or +appendages, each of which consists of a stalk and two terminal pieces. So +that I can represent a transverse section of the ring and its appendages +upon the diagram board in this way. + +If I now take the fourth ring, I find it has the same structure, and so +have the fifth and the second; so that, in each of these divisions of the +tail, I find parts which correspond with one another, a ring and two +appendages; and in each appendage a stalk and two end pieces. These +corresponding parts are called, in the technical language of anatomy, +"homologous parts." The ring of the third division is the "homologue" of +the ring of the fifth, the appendage of the former is the homologue of +the appendage of the latter. And, as each division exhibits corresponding +parts in corresponding places, we say that all the divisions are +constructed upon the same plan. But now let us consider the sixth +division. It is similar to, and yet different from, the others. The ring +is essentially the same as in the other divisions; but the appendages +look at first as if they were very different; and yet when we regard them +closely, what do we find? A stalk and two terminal divisions, exactly as +in the others, but the stalk is very short and very thick, the terminal +divisions are very broad and flat, and one of them is divided into two +pieces. + +I may say, therefore, that the sixth segment is like the others in plan, +but that it is modified in its details. + +The first segment is like the others, so far as its ring is concerned, +and though its appendages differ from any of those yet examined in the +simplicity of their structure, parts corresponding with the stem and one +of the divisions of the appendages of the other segments can be readily +discerned in them. + +Thus it appears that the lobster's tail is composed of a series of +segments which are fundamentally similar, though each presents peculiar +modifications of the plan common to all. But when I turn to the forepart +of the body I see, at first, nothing but a great shield-like shell, +called technically the "carapace," ending in front in a sharp spine, on +either side of which are the curious compound eyes, set upon the ends of +stout movable stalks. Behind these, on the under side of the body, are +two pairs of long feelers, or antennae, followed by six pairs of jaws +folded against one another over the mouth, and five pairs of legs, the +foremost of these being the great pinchers, or claws, of the lobster. + +It looks, at first, a little hopeless to attempt to find in this complex +mass a series of rings, each with its pair of appendages, such as I have +shown you in the abdomen, and yet it is not difficult to demonstrate +their existence. Strip off the legs, and you will find that each pair is +attached to a very definite segment of the under wall of the body; but +these segments, instead of being the lower parts of free rings, as in the +tail, are such parts of rings which are all solidly united and bound +together; and the like is true of the jaws, the feelers, and the eye- +stalks, every pair of which is borne upon its own special segment. Thus +the conclusion is gradually forced upon us, that the body of the lobster +is composed of as many rings as there are pairs of appendages, namely, +twenty in all, but that the six hindmost rings remain free and movable, +while the fourteen front rings become firmly soldered together, their +backs forming one continuous shield--the carapace. + +Unity of plan, diversity in execution, is the lesson taught by the study +of the rings of the body, and the same instruction is given still more +emphatically by the appendages. If I examine the outermost jaw I find it +consists of three distinct portions, an inner, a middle, and an outer, +mounted upon a common stem; and if I compare this jaw with the legs +behind it, or the jaws in front of it, I find it quite easy to see, that, +in the legs, it is the part of the appendage which corresponds with the +inner division, which becomes modified into what we know familiarly as +the "leg," while the middle division disappears, and the outer division +is hidden under the carapace. Nor is it more difficult to discern that, +in the appendages of the tail, the middle division appears again and the +outer vanishes; while, on the other hand, in the foremost jaw, the so- +called mandible, the inner division only is left; and, in the same way, +the parts of the feelers and of the eye-stalks can be identified with +those of the legs and jaws. + +But whither does all this tend? To the very remarkable conclusion that a +unity of plan, of the same kind as that discoverable in the tail or +abdomen of the lobster, pervades the whole organisation of its skeleton, +so that I can return to the diagram representing any one of the rings of +the tail, which I drew upon the board, and by adding a third division to +each appendage, I can use it as a sort of scheme or plan of any ring of +the body. I can give names to all the parts of that figure, and then if I +take any segment of the body of the lobster, I can point out to you +exactly, what modification the general plan has undergone in that +particular segment; what part has remained movable, and what has become +fixed to another; what has been excessively developed and metamorphosed +and what has been suppressed. + +But I imagine I hear the question, How is all this to be tested? No doubt +it is a pretty and ingenious way of looking at the structure of any +animal; but is it anything more? Does Nature acknowledge, in any deeper +way, this unity of plan we seem to trace? + +The objection suggested by these questions is a very valid and important +one, and morphology was in an unsound state so long as it rested upon the +mere perception of the analogies which obtain between fully formed parts. +The unchecked ingenuity of speculative anatomists proved itself fully +competent to spin any number of contradictory hypotheses out of the same +facts, and endless morphological dreams threatened to supplant scientific +theory. + +Happily, however, there is a criterion of morphological truth, and a sure +test of all homologies. Our lobster has not always been what we see it; +it was once an egg, a semifluid mass of yolk, not so big as a pin's head, +contained in a transparent membrane, and exhibiting not the least trace +of any one of those organs, the multiplicity and complexity of which, in +the adult, are so surprising. After a time, a delicate patch of cellular +membrane appeared upon one face of this yolk, and that patch was the +foundation of the whole creature, the clay out of which it would be +moulded. Gradually investing the yolk, it became subdivided by transverse +constrictions into segments, the forerunners of the rings of the body. +Upon the ventral surface of each of the rings thus sketched out, a pair +of bud-like prominences made their appearance--the rudiments of the +appendages of the ring. At first, all the appendages were alike, but, as +they grew, most of them became distinguished into a stem and two terminal +divisions, to which, in the middle part of the body, was added a third +outer division; and it was only at a later period, that by the +modification, or absorption, of certain of these primitive constituents, +the limbs acquired their perfect form. + +Thus the study of development proves that the doctrine of unity of plan +is not merely a fancy, that it is not merely one way of looking at the +matter, but that it is the expression of deep-seated natural facts. The +legs and jaws of the lobster may not merely be regarded as modifications +of a common type,--in fact and in nature they are so,--the leg and the +jaw of the young animal being, at first, indistinguishable. + +These are wonderful truths, the more so because the zoologist finds them +to be of universal application. The investigation of a polype, of a +snail, of a fish, of a horse, or of a man, would have led us, though by a +less easy path, perhaps, to exactly the same point. Unity of plan +everywhere lies hidden under the mask of diversity of structure--the +complex is everywhere evolved out of the simple. Every animal has at +first the form of an egg, and every animal and every organic part, in +reaching its adult state, passes through conditions common to other +animals and other adult parts; and this leads me to another point. I have +hitherto spoken as if the lobster were alone in the world, but, as I need +hardly remind you, there are myriads of other animal organisms. Of these, +some, such as men, horses, birds, fishes, snails, slugs, oysters, corals, +and sponges, are not in the least like the lobster. But other animals, +though they may differ a good deal from the lobster, are yet either very +like it, or are like something that is like it. The cray fish, the rock +lobster, and the prawn, and the shrimp, for example, however different, +are yet so like lobsters, that a child would group them as of the lobster +kind, in contradistinction to snails and slugs; and these last again +would form a kind by themselves, in contradistinction to cows, horses, +and sheep, the cattle kind. + +But this spontaneous grouping into "kinds" is the first essay of the +human mind at classification, or the calling by a common name of those +things that are alike, and the arranging them in such a manner as best to +suggest the sum of their likenesses and unlikenesses to other things. + +Those kinds which include no other subdivisions than the sexes, or +various breeds, are called, in technical language, species. The English +lobster is a species, our cray fish is another, our prawn is another. In +other countries, however, there are lobsters, cray fish, and prawns, very +like ours, and yet presenting sufficient differences to deserve +distinction. Naturalists, therefore, express this resemblance and this +diversity by grouping them as distinct species of the same "genus." But +the lobster and the cray fish, though belonging to distinct genera, have +many features in common, and hence are grouped together in an assemblage +which is called a family. More distant resemblances connect the lobster +with the prawn and the crab, which are expressed by putting all these +into the same order. Again, more remote, but still very definite, +resemblances unite the lobster with the woodlouse, the king crab, the +water flea, and the barnacle, and separate them from all other animals; +whence they collectively constitute the larger group, or class, +_Crustacea_. But the _Crustacea_ exhibit many peculiar features in common +with insects, spiders, and centipedes, so that these are grouped into the +still larger assemblage or "province" _Articulata_; and, finally, the +relations which these have to worms and other lower animals, are +expressed by combining the whole vast aggregate into the sub-kingdom of +_Annulosa_. + +If I had worked my way from a sponge instead of a lobster, I should have +found it associated, by like ties, with a great number of other animals +into the sub-kingdom _Protozoa_; if I had selected a fresh-water polype +or a coral, the members of what naturalists term the sub-kingdom +_Coelenterata_, would have grouped themselves around my type; had a snail +been chosen, the inhabitants of all univalve and bivalve, land and water, +shells, the lamp shells, the squids, and the sea-mat would have gradually +linked themselves on to it as members of the same sub-kingdom of +_Mollusca_; and finally, starting from man, I should have been compelled +to admit first, the ape, the rat, the horse, the dog, into the same +class; and then the bird, the crocodile, the turtle, the frog, and the +fish, into the same sub-kingdom of _Vertebrata_. + +And if I had followed out all these various lines of classification +fully, I should discover in the end that there was no animal, either +recent or fossil, which did not at once fall into one or other of these +sub-kingdoms. In other words, every animal is organised upon one or other +of the five, or more, plans, the existence of which renders our +classification possible. And so definitely and precisely marked is the +structure of each animal, that, in the present state of our knowledge, +there is not the least evidence to prove that a form, in the slightest +degree transitional between any of the two groups _Vertebrata, Annulosa, +Mollusca_, and _Coelenterata_, either exists, or has existed, during that +period of the earth's history which is recorded by the geologist.[1] +Nevertheless, you must not for a moment suppose, because no such +transitional forms are known, that the members of the sub-kingdoms are +disconnected from, or independent of, one another. On the contrary, in +their earliest condition they are all similar, and the primordial germs +of a man, a dog, a bird, a fish, a beetle, a snail, and a polype are, in +no essential structural respects, distinguishable. + +[Footnote 1: The different grouping necessitated by later knowledge does +not affect the principle of the argument.--1894.] + +In this broad sense, it may with truth be said, that all living animals, +and all those dead faunae which geology reveals, are bound together by an +all-pervading unity of organisation, of the same character, though not +equal in degree, to that which enables us to discern one and the same +plan amidst the twenty different segments of a lobster's body. Truly it +has been said, that to a clear eye the smallest fact is a window through +which the Infinite may be seen. + +Turning from these purely morphological considerations, let us now +examine into the manner in which the attentive study of the lobster +impels us into other lines of research. + +Lobsters are found in all the European seas; but on the opposite shores +of the Atlantic and in the seas of the southern hemisphere they do not +exist. They are, however, represented in these regions by very closely +allied, but distinct forms--the _Homarus Americanus_ and the _Homarus +Capensis:_ so that we may say that the European has one species of +_Homuarus_; the American, another; the African, another; and thus the +remarkable facts of geographical distribution begin to dawn upon us. + +Again, if we examine the contents of the earth's crust, we shall find in +the latter of those deposits, which have served as the great burying +grounds of past ages, numberless lobster-like animals, but none so +similar to our living lobster as to make zoologists sure that they +belonged even to the same genus. If we go still further back in time, we +discover, in the oldest rocks of all, the remains of animals, constructed +on the same general plan as the lobster, and belonging to the same great +group of _Crustacea_; but for the most part totally different from the +lobster, and indeed from any other living form of crustacean; and thus we +gain a notion of that successive change of the animal population of the +globe, in past ages, which is the most striking fact revealed by geology. + +Consider, now, where our inquiries have led us. We studied our type +morphologically, when we determined its anatomy and its development, and +when comparing it, in these respects, with other animals, we made out its +place in a system of classification. If we were to examine every animal +in a similar manner, we should establish a complete body of zoological +morphology. + +Again, we investigated the distribution of our type in space and in time, +and, if the like had been done with every animal, the sciences of +geographical and geological distribution would have attained their limit. + +But you will observe one remarkable circumstance, that, up to this point, +the question of the life of these organisms has not come under +consideration. Morphology and distribution might be studied almost as +well, if animals and plants were a peculiar kind of crystals, and +possessed none of those functions which distinguish living beings so +remarkably. But the facts of morphology and distribution have to be +accounted for, and the science, the aim of which it is to account for +them, is Physiology. + +Let us return to our lobster once more. If we watched the creature in its +native element, we should see it climbing actively the submerged rocks, +among which it delights to live, by means of its strong legs; or swimming +by powerful strokes of its great tail, the appendages of the sixth joint +of which are spread out into a broad fan-like Propeller: seize it, and it +will show you that its great claws are no mean weapons of offence; +suspend a piece of carrion among its haunts, and it will greedily devour +it, tearing and crushing the flesh by means of its multitudinous jaws. + +Suppose that we had known nothing of the lobster but as an inert mass, an +organic crystal, if I may use the phrase, and that we could suddenly see +it exerting all these powers, what wonderful new ideas and new questions +would arise in our minds! The great new question would be, "How does all +this take place?" the chief new idea would be, the idea of adaptation to +purpose,--the notion, that the constituents of animal bodies are not mere +unconnected parts, but organs working together to an end. Let us consider +the tail of the lobster again from this point of view. Morphology has +taught us that it is a series of segments composed of homologous parts, +which undergo various modifications--beneath and through which a common +plan of formation is discernible. But if I look at the same part +physiologically, I see that it is a most beautifully constructed organ of +locomotion, by means of which the animal can swiftly propel itself either +backwards or forwards. + +But how is this remarkable propulsive machine made to perform its +functions? If I were suddenly to kill one of these animals and to take +out all the soft parts, I should find the shell to be perfectly inert, to +have no more power of moving itself than is possessed by the machinery of +a mill when disconnected from its steam-engine or water-wheel. But if I +were to open it, and take out the viscera only, leaving the white flesh, +I should perceive that the lobster could bend and extend its tail as well +as before. If I were to cut off the tail, I should cease to find any +spontaneous motion in it; but on pinching any portion of the flesh, I +should observe that it underwent a very curious change--each fibre +becoming shorter and thicker. By this act of contraction, as it is +termed, the parts to which the ends of the fibre are attached are, of +course, approximated; and according to the relations of their points of +attachment to the centres of motions of the different rings, the bending +or the extension of the tail results. Close observation of the newly- +opened lobster would soon show that all its movements are due to the same +cause--the shortening and thickening of these fleshy fibres, which are +technically called muscles. + +Here, then, is a capital fact. The movements of the lobster are due to +muscular contractility. But why does a muscle contract at one time and +not at another? Why does one whole group of muscles contract when the +lobster wishes to extend his tail, and another group when he desires to +bend it? What is it originates, directs, and controls the motive power? + +Experiment, the great instrument for the ascertainment of truth in +physical science, answers this question for us. In the head of the +lobster there lies a small mass of that peculiar tissue which is known as +nervous substance. Cords of similar matter connect his brain of the +lobster, directly or indirectly, with the muscles. Now, if these +communicating cords are cut, the brain remaining entire, the power of +exerting what we call voluntary motion in the parts below the section is +destroyed; and, on the other hand, if, the cords remaining entire, the +brain mass be destroyed, the same voluntary mobility is equally lost. +Whence the inevitable conclusion is, that the power of originating these +motions resides in the brain and is propagated along the nervous cords. + +In the higher animals the phenomena which attend this transmission have +been investigated, and the exertion of the peculiar energy which resides +in the nerves has been found to be accompanied by a disturbance of the +electrical state of their molecules. + +If we could exactly estimate the signification of this disturbance; if we +could obtain the value of a given exertion of nerve force by determining +the quantity of electricity, or of heat, of which it is the equivalent; +if we could ascertain upon what arrangement, or other condition of the +molecules of matter, the manifestation of the nervous and muscular +energies depends (and doubtless science will some day or other ascertain +these points), physiologists would have attained their ultimate goal in +this direction; they would have determined the relation of the motive +force of animals to the other forms of force found in nature; and if the +same process had been successfully performed for all the operations which +are carried on in, and by, the animal frame, physiology would be perfect, +and the facts of morphology and distribution would be deducible from the +laws which physiologists had established, combined with those determining +the condition of the surrounding universe. + +There is not a fragment of the organism of this humble animal whose study +would not lead us into regions of thought as large as those which I have +briefly opened up to you; but what I have been saying, I trust, has not +only enabled you to form a conception of the scope and purport of +zoology, but has given you an imperfect example of the manner in which, +in my opinion, that science, or indeed any physical science, may be best +taught. The great matter is, to make teaching real and practical, by +fixing the attention of the student on particular facts; but at the same +time it should be rendered broad and comprehensive, by constant reference +to the generalisations of which all particular facts are illustrations. +The lobster has served as a type of the whole animal kingdom, and its +anatomy and physiology have illustrated for us some of the greatest +truths of biology. The student who has once seen for himself the facts +which I have described, has had their relations explained to him, and has +clearly comprehended them, has, so far, a knowledge of zoology, which is +real and genuine, however limited it may be, and which is worth more than +all the mere reading knowledge of the science he could ever acquire. His +zoological information is, so far, knowledge and not mere hearsay. + +And if it were nay business to fit you for the certificate in zoological +science granted by this department, I should pursue a course precisely +similar in principle to that which I have taken to-night. I should select +a fresh-water sponge, a fresh-water polype or a _Cyanoea_, a fresh-water +mussel, a lobster, a fowl, as types of the five primary divisions of the +animal kingdom. I should explain their structure very fully, and show how +each illustrated the great principles of zoology. Having gone very +carefully and fully over this ground, I should feel that you had a safe +foundation, and I should then take you in the same way, but less +minutely, over similarly selected illustrative types of the classes; and +then I should direct your attention to the special forms enumerated under +the head of types, in this syllabus, and to the other facts there +mentioned. + +That would, speaking generally, be my plan. But I have undertaken to +explain to you the best mode of acquiring and communicating a knowledge +of zoology, and you may therefore fairly ask me for a more detailed and +precise account of the manner in which I should propose to furnish you +with the information I refer to. + +My own impression is, that the best model for all kinds of training in +physical science is that afforded by the method of teaching anatomy, in +use in the medical schools. This method consists of three elements-- +lectures, demonstrations, and examinations. + +The object of lectures is, in the first place, to awaken the attention +and excite the enthusiasm of the student; and this, I am sure, may be +effected to a far greater extent by the oral discourse and by the +personal influence of a respected teacher than in any other way. +Secondly, lectures have the double use of guiding the student to the +salient points of a subject, and at the same time forcing him to attend +to the whole of it, and not merely to that part which takes his fancy. +And lastly, lectures afford the student the opportunity of seeking +explanations of those difficulties which will, and indeed ought to, arise +in the course of his studies. + +What books shall I read? is a question constantly put by the student to +the teacher. My reply usually is, "None: write your notes out carefully +and fully; strive to understand them thoroughly; come to me for the +explanation of anything you cannot understand; and I would rather you did +not distract your mind by reading." A properly composed course of +lectures ought to contain fully as much matter as a student can +assimilate in the time occupied by its delivery; and the teacher should +always recollect that his business is to feed, and not to cram the +intellect. Indeed, I believe that a student who gains from a course of +lectures the simple habit of concentrating his attention upon a +definitely limited series of facts, until they are thoroughly mastered, +has made a step of immeasurable importance. + +But, however good lectures may be, and however extensive the course of +reading by which they are followed up, they are but accessories to the +great instrument of scientific teaching--demonstration. If I insist +unweariedly, nay fanatically, upon the importance of physical science as +an educational agent, it is because the study of any branch of science, +if properly conducted, appears to me to fill up a void left by all other +means of education. I have the greatest respect and love for literature; +nothing would grieve me more than to see literary training other than a +very prominent branch of education: indeed, I wish that real literary +discipline were far more attended to than it is; but I cannot shut my +eyes to the fact, that there is a vast difference between men who have +had a purely literary, and those who have had a sound scientific, +training. + +Seeking for the cause of this difference, I imagine I can find it in the +fact that, in the world of letters, learning and knowledge are one, and +books are the source of both; whereas in science, as in life, learning +and knowledge are distinct, and the study of things, and not of books, is +the source of the latter. + +All that literature has to bestow may be obtained by reading and by +practical exercise in writing and in speaking; but I do not exaggerate +when I say, that none of the best gifts of science are to be won by these +means. On the contrary, the great benefit which a scientific education +bestows, whether is training or as knowledge, is dependent upon the +extent to which the mind of the student is brought into immediate contact +with facts--upon the degree to which he learns the habit of appealing +directly to Nature, and of acquiring through his senses concrete images +of those properties of things, which are, and always will be, but +approximatively expressed in human language. Our way of looking at +Nature, and of speaking about her, varies from year to year; but a fact +once seen, a relation of cause and effect, once demonstratively +apprehended, are possessions which neither change nor pass away, but, on +the contrary, form fixed centres, about which other truths aggregate by +natural affinity. + +Therefore, the great business of the scientific teacher is, to imprint +the fundamental, irrefragable facts of his science, not only by words +upon the mind, but by sensible impressions upon the eye, and ear, and +touch of the student, in so complete a manner, that every term used, or +law enunciated, should afterwards call up vivid images of the particular +structural, or other, facts which furnished the demonstration of the law, +or the illustration of the term. + +Now this important operation can only be achieved by constant +demonstration, which may take place to a certain imperfect extent during +a lecture, but which ought also to be carried on independently, and which +should be addressed to each individual student, the teacher endeavouring, +not so much to show a thing to the learner, as to make him see it for +himself. + +I am well aware that there are great practical difficulties in the way of +effectual zoological demonstrations. The dissection of animals is not +altogether pleasant, and requires much time; nor is it easy to secure an +adequate supply of the needful specimens. The botanist has here a great +advantage; his specimens are easily obtained, are clean and wholesome, +and can be dissected in a private house as well as anywhere else; and +hence, I believe, the fact, that botany is so much more readily and +better taught than its sister science. But, be it difficult or be it +easy, if zoological science is to be properly studied, demonstration, +and, consequently, dissection, must be had. Without it, no man can have a +really sound knowledge of animal organisation. + +A good deal may be done, however, without actual dissection on the +student's part, by demonstration upon specimens and preparations; and in +all probability it would not be very difficult, were the demand +sufficient, to organise collections of such objects, sufficient for all +the purposes of elementary teaching, at a comparatively cheap rate. Even +without these, much might be effected, if the zoological collections, +which are open to the public, were arranged according to what has been +termed the "typical principle"; that is to say, if the specimens exposed +to public view were so selected that the public could learn something +from them, instead of being, as at present, merely confused by their +multiplicity. For example, the grand ornithological gallery at the +British Museum contains between two and three thousand species of birds, +and sometimes five or six specimens of a species. They are very pretty to +look at, and some of the cases are, indeed, splendid; but I will +undertake to say, that no man but a professed ornithologist has ever +gathered much information from the collection. Certainly, no one of the +tens of thousands of the general public who have walked through that +gallery ever knew more about the essential peculiarities of birds when he +left the gallery than when he entered it. But if, somewhere in that vast +hall, there were a few preparations, exemplifying the leading structural +peculiarities and the mode of development of a common fowl; if the types +of the genera, the leading modifications in the skeleton, in the plumage +at various ages, in the mode of nidification, and the like, among birds, +were displayed; and if the other specimens were put away in a place where +the men of science, to whom they are alone useful, could have free access +to them, I can conceive that this collection might become a great +instrument of scientific education. + +The last implement of the teacher to which I have adverted is +examination--a means of education now so thoroughly understood that I +need hardly enlarge upon it. I hold that both written and oral +examinations are indispensable, and, by requiring the description of +specimens, they may be made to supplement demonstration. + +Such is the fullest reply the time at my disposal will allow me to give +to the question--how may a knowledge of zoology be best acquired and +communicated? + +But there is a previous question which may be moved, and which, in fact, +I know many are inclined to move. It is the question, why should teachers +be encouraged to acquire a knowledge of this, or any other branch of +physical science? What is the use, it is said, of attempting to make +physical science a branch of primary education? Is it not probable that +teachers, in pursuing such studies, will be led astray from the +acquirement of more important but less attractive knowledge? And, even if +they can learn something of science without prejudice to their +usefulness, what is the good of their attempting to instil that knowledge +into boys whose real business is the acquisition of reading, writing, and +arithmetic? + +These questions are, and will be, very commonly asked, for they arise +from that profound ignorance of the value and true position of physical +science, which infests the minds of the most highly educated and +intelligent classes of the community. But if I did not feel well assured +that they are capable of being easily and satisfactorily answered; that +they have been answered over and over again; and that the time will come +when men of liberal education will blush to raise such questions--I +should be ashamed of my position here to-night. Without doubt, it is your +great and very important function to carry out elementary education; +without question, anything that should interfere with the faithful +fulfilment of that duty on your part would be a great evil; and if I +thought that your acquirement of the elements of physical science, and +your communication of those elements to your pupils, involved any sort of +interference with your proper duties, I should be the first person to +protest against your being encouraged to do anything of the kind. + +But is it true that the acquisition of such a knowledge of science as is +proposed, and the communication of that knowledge, are calculated to +weaken your usefulness? Or may I not rather ask, is it possible for you +to discharge your functions properly without these aids? + +What is the purpose of primary intellectual education? I apprehend that +its first object is to train the young in the use of those tools +wherewith men extract knowledge from the ever-shifting succession of +phenomena which pass before their eyes; and that its second object is to +inform them of the fundamental laws which have been found by experience +to govern the course of things, so that they may not be turned out into +the world naked, defenceless, and a prey to the events they might +control. + +A boy is taught to read his own and other languages, in order that he may +have access to infinitely wider stores of knowledge than could ever be +opened to him by oral intercourse with his fellow men; he learns to +write, that his means of communication with the rest of mankind may be +indefinitely enlarged, and that he may record and store up the knowledge +he acquires. He is taught elementary mathematics, that he may understand +all those relations of number and form, upon which the transactions of +men, associated in complicated societies, are built, and that he may have +some practice in deductive reasoning. + +All these operations of reading, writing, and ciphering, are intellectual +tools, whose use should, before all things, be learned, and learned +thoroughly; so that the youth may be enabled to make his life that which +it ought to be, a continual progress in learning and in wisdom. + +But, in addition, primary education endeavours to fit a boy out with a +certain equipment of positive knowledge. He is taught the great laws of +morality; the religion of his sect; so much history and geography as will +tell him where the great countries of the world are, what they are, and +how they have become what they are. + +Without doubt all these are most fitting and excellent things to teach a +boy; I should be very sorry to omit any of them from any scheme of +primary intellectual education. The system is excellent, so far as it +goes. + +But if I regard it closely, a curious reflection arises. I suppose that, +fifteen hundred years ago, the child of any well-to-do Roman citizen was +taught just these same things; reading and writing in his own, and, +perhaps, the Greek tongue; the elements of mathematics; and the religion, +morality, history, and geography current in his time. Furthermore, I do +not think I err in affirming, that, if such a Christian Roman boy, who +had finished his education, could be transplanted into one of our public +schools, and pass through its course of instruction, he would not meet +with a single unfamiliar line of thought; amidst all the new facts he +would have to learn, not one would suggest a different mode of regarding +the universe from that current in his own time. + +And yet surely there is some great difference between the civilisation of +the fourth century and that of the nineteenth, and still more between the +intellectual habits and tone of thought of that day and this? + +And what has made this difference? I answer fearlessly--The prodigious +development of physical science within the last two centuries. + +Modern civilisation rests upon physical science; take away her gifts to +our own country, and our position among the leading nations of the world +is gone to-morrow; for it is physical science only that makes +intelligence and moral energy stronger than brute force. + +The whole of modern thought is steeped in science; it has made its way +into the works of our best poets, and even the mere man of letters, who +affects to ignore and despise science, is unconsciously impregnated with +her spirit, and indebted for his best products to her methods. I believe +that the greatest intellectual revolution mankind has yet seen is now +slowly taking place by her agency. She is teaching the world that the +ultimate court of appeal is observation and experiment, and not +authority; she is teaching it to estimate the value of evidence; she is +creating a firm and living faith in the existence of immutable moral and +physical laws, perfect obedience to which is the highest possible aim of +an intelligent being. + +But of all this your old stereotyped system of education takes no note. +Physical science, its methods, its problems, and its difficulties, will +meet the poorest boy at every turn, and yet we educate him in such a +manner that he shall enter the world as ignorant of the existence of the +methods and facts of science as the day he was born. The modern world is +full of artillery; and we turn out our children to do battle in it, +equipped with the shield and sword of an ancient gladiator. + +Posterity will cry shame on us if we do not remedy this deplorable state +of things. Nay, if we live twenty years longer, our own consciences will +cry shame on us. + +It is my firm conviction that the only way to remedy it is to make the +elements of physical science an integral part of primary education. I +have endeavoured to show you how that may be done for that branch of +science which it is my business to pursue; and I can but add, that I +should look upon the day when every schoolmaster throughout this land was +a centre of genuine, however rudimentary, scientific knowledge, as an +epoch in the history of the country. + +But let me entreat you to remember my last words. Addressing myself to +you, as teachers, I would say, mere book learning in physical science is +a sham and a delusion--what you teach, unless you wish to be impostors, +that you must first know; and real knowledge in science means personal +acquaintance with the facts, be they few or many.[2] + +[Footnote 2: It has been suggested to me that these words may be taken to +imply a discouragement on my part of any sort of scientific instruction +which does not give an acquaintance with the facts at first hand. But +this is not my meaning. The ideal of scientific teaching is, no doubt, a +system by which the scholar sees every fact for himself, and the teacher +supplies only the explanations. Circumstances, however, do not often +allow of the attainment of that ideal, and we must put up with the next +best system--one in which the scholar takes a good deal on trust from a +teacher, who, knowing the facts by his own knowledge, can describe them +with so much vividness as to enable his audience to form competent ideas +concerning them. The system which I repudiate is that which allows +teachers who have not come into direct contact with the leading facts of +a science to pass their second-hand information on. The scientific virus, +like vaccine lymph, if passed through too long a succession of organisms, +will lose all its effect in protecting the young against the intellectual +epidemics to which they are exposed. + +[The remarks on p. 222 applied to the Natural History Collection of the +British Museum in 1861. The visitor to the Natural History Museum in 1894 +need go no further than the Great Hall to see the realisation of my hopes +by the present Director.]] + + + +VIII + + +BIOGENESIS AND ABIOGENESIS + +(THE PRESIDENTIAL ADDRESS TO THE BRITISH ASSOCIATION FOR THE ADVANCEMENT +OF SCIENCE FOR 1870) + +It has long been the custom for the newly installed President of the +British Association for the Advancement of Science to take advantage of +the elevation of the position in which the suffrages of his colleagues +had, for the time, placed him, and, casting his eyes around the horizon +of the scientific world, to report to them what could be seen from his +watch-tower; in what directions the multitudinous divisions of the noble +army of the improvers of natural knowledge were marching; what important +strongholds of the great enemy of us all, ignorance, had been recently +captured; and, also, with due impartiality, to mark where the advanced +posts of science had been driven in, or a long-continued siege had made +no progress. + +I propose to endeavour to follow this ancient precedent, in a manner +suited to the limitations of my knowledge and of my capacity. I shall not +presume to attempt a panoramic survey of the world of science, nor even +to give a sketch of what is doing in the one great province of biology, +with some portions of which my ordinary occupations render me familiar. +But I shall endeavour to put before you the history of the rise and +progress of a single biological doctrine; and I shall try to give some +notion of the fruits, both intellectual and practical, which we owe, +directly or indirectly, to the working out, by seven generations of +patient and laborious investigators, of the thought which arose, more +than two centuries ago, in the mind of a sagacious and observant Italian +naturalist. + +It is a matter of everyday experience that it is difficult to prevent +many articles of food from becoming covered with mould; that fruit, sound +enough to all appearance, often contains grubs at the core; that meat, +left to itself in the air, is apt to putrefy and swarm with maggots. Even +ordinary water, if allowed to stand in an open vessel, sooner or later +becomes turbid and full of living matter. + +The philosophers of antiquity, interrogated as to the cause of these +phenomena, were provided with a ready and a plausible answer. It did not +enter their minds even to doubt that these low forms of life were +generated in the matters in which they made their appearance. Lucretius, +who had drunk deeper of the scientific spirit than any poet of ancient or +modern times except Goethe, intends to speak as a philosopher, rather +than as a poet, when he writes that "with good reason the earth has +gotten the name of mother, since all things are produced out of the +earth. And many living creatures, even now, spring out of the earth, +taking form by the rains and the heat of the sun."[1] The axiom of +ancient science, "that the corruption of one thing is the birth of +another," had its popular embodiment in the notion that a seed dies +before the young plant springs from it; a belief so widespread and so +fixed, that Saint Paul appeals to it in one of the most splendid +outbursts of his fervid eloquence:-- + +"Thou fool, that which thou sowest is not quickened, except it die."[2] + +[Footnote 1: It is thus that Mr. Munro renders + +"Linquitur, ut merito maternum nomen adepta +Terra sit, e terra quoniam sunt cuncta creata. +Multaque nunc etiam exsistant animalia terris +Imbribus et calido solis concreta vapore." + +_De Rerum Natura_, lib. v. 793-796. + +But would not the meaning of the last line be better rendered "Developed +in rain-water and in the warm vapours raised by the sun"?] + +[Footnote 2: 1 Corinthians xv. 36.] + +The proposition that life may, and does, proceed from that which has no +life, then, was held alike by the philosophers, the poets, and the +people, of the most enlightened nations, eighteen hundred years ago; and +it remained the accepted doctrine of learned and unlearned Europe, +through the Middle Ages, down even to the seventeenth century. + +It is commonly counted among the many merits of our great countryman, +Harvey, that he was the first to declare the opposition of fact to +venerable authority in this, as in other matters; but I can discover no +justification for this widespread notion. After careful search through +the "Exercitationes de Generatione," the most that appears clear to me +is, that Harvey believed all animals and plants to spring from what he +terms a "_primordium vegetale_," a phrase which may nowadays be rendered +"a vegetative germ"; and this, he says, is _"oviforme_," or "egg-like"; +not, he is careful to add, that it necessarily has the shape of an egg, +but because it has the constitution and nature of one. That this +"_primordium oviforme_" must needs, in all cases, proceed from a living +parent is nowhere expressly maintained by Harvey, though such an opinion +may be thought to be implied in one or two passages; while, on the other +hand, he does, more than once, use language which is consistent only with +a full belief in spontaneous or equivocal generation.[3] In fact, the +main concern of Harvey's wonderful little treatise is not with +generation, in the physiological sense, at all, but with development; and +his great object is the establishment of the doctrine of epigenesis. + +[Footnote 3: See the following passage in Exercitatio I.:--"Item _sponte +nascentia_ dicuntur; non quod ex _putredine_ oriunda sint, sed quod casu, +naturae sponte, et aequivocâ (ut aiunt) generatione, a parentibus sui +dissimilibus proveniant." Again, in _De Uteri Membranis:_--"In cunctorum +viventium generatione (sicut diximus) hoc solenne est, ut ortum ducunt a +_primordio_ aliquo, quod tum materiam tum elficiendi potestatem in se +habet: sitque, adeo id, ex quo et a quo quicquid nascitur, ortum suum +ducat. Tale primordium in animalibus (_sive ab aliis generantibus +proveniant, sive sponte, aut ex putredine nascentur_) est humor in +tunicâ, aliquâaut putami ne conclusus." Compare also what Redi has to say +respecting Harvey's opinions, _Esperienze_, p. 11.] + +The first distinct enunciation of the hypothesis that all living matter +has sprung from pre-existing living matter, came from a contemporary, +though a junior, of Harvey, a native of that country, fertile in men +great in all departments of human activity, which was to intellectual +Europe, in the sixteenth and seventeenth centuries, what Germany is in +the nineteenth. It was in Italy, and from Italian teachers, that Harvey +received the most important part of his scientific education. And it was +a student trained in the same schools, Francesco Redi--a man of the +widest knowledge and most versatile abilities, distinguished alike as +scholar, poet, physician, and naturalist--who, just two hundred and two +years ago, published his "Esperienze intorno alla Generazione degl' +Insetti," and gave to the world the idea, the growth of which it is my +purpose to trace. Redi's book went through five editions in twenty years; +and the extreme simplicity of his experiments, and the clearness of his +arguments, gained for his views, and for their consequences, almost +universal acceptance. + +Redi did not trouble himself much with speculative considerations, but +attacked particular cases of what was supposed to be "spontaneous +generation" experimentally. Here are dead animals, or pieces of meat, +says he; I expose them to the air in hot weather, and in a few days they +swarm with maggots. You tell me that these are generated in the dead +flesh; but if I put similar bodies, while quite fresh, into a jar, and +tie some fine gauze over the top of the jar, not a maggot makes its +appearance, while the dead substances, nevertheless, putrefy just in the +same way as before. It is obvious, therefore, that the maggots are not +generated by the corruption of the meat; and that the cause of their +formation must be a something which is kept away by gauze. But gauze will +not keep away aëriform bodies, or fluids. This something must, therefore, +exist in the form of solid particles too big to get through the gauze. +Nor is one long left in doubt what these solid particles are; for the +blowflies, attracted by the odour of the meat, swarm round the vessel, +and, urged by a powerful but in this case misleading instinct, lay eggs +out of which maggots are immediately hatched, upon the gauze. The +conclusion, therefore, is unavoidable; the maggots are not generated by +the meat, but the eggs which give rise to them are brought through the +air by the flies. + +These experiments seem almost childishly simple, and one wonders how it +was that no one ever thought of them before. Simple as they are, however, +they are worthy of the most careful study, for every piece of +experimental work since done, in regard to this subject, has been shaped +upon the model furnished by the Italian philosopher. As the results of +his experiments were the same, however varied the nature of the materials +he used, it is not wonderful that there arose in Redi's mind a +presumption, that, in all such cases of the seeming production of life +from dead matter, the real explanation was the introduction of living +germs from without into that dead matter.[4] And thus the hypothesis that +living matter always arises by the agency of pre-existing living matter, +took definite shape; and had, henceforward, a right to be considered and +a claim to be refuted, in each particular case, before the production of +living matter in any other way could be admitted by careful reasoners. It +will be necessary for me to refer to this hypothesis so frequently, that, +to save circumlocution, I shall call it the hypothesis of _Biogenesis_; +and I shall term the contrary doctrine--that living matter may be +produced by not living matter--the hypothesis of _Abiogenesis_. + +[Footnote 4: "Pure contentandomi sempre in questa ed in ciascuna altro +cosa, da ciascuno più savio, là dove io difettuosamente parlassi, esser +corretto; non tacero, che per molte osservazioni molti volti da me fatte, +mi sento inclinato a credere che la terra, da quelle prime piante, e da +quei primi animali in poi, che ella nei primi giorni del mondo produsse +per comandemento del sovrano ed omnipotente Fattore, non abbia mai più +prodotto da se medesima nè erba nè albero, nè animale alcuno perfetto o +imperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassati +è nato e che ora nascere in lei, o da lei veggiamo, venga tutto dalla +semenza reale e vera delle piante, e degli animali stessi, i quali col +mezzo del proprio seme la loro spezie conservano. E se bene tutto giorno +scorghiamo da' cadaveri degli animali, e da tutte quante le maniere dell' +erbe, e de' fiori, e dei frutti imputriditi, e corrotti nascere vermi +infiniti-- + +'Nonne vides quaecunque mora, fluidoque calore +Corpora tabescunt in parva animalia verti'-- + +Io mi sento, dico, inclinato, a credere che tutti quei vermi si generino +dal seme paterno; e che le carni, e l' erbe, e l' altre cose tutte +putrefatte, o putrefattibili non facciano altra parte, nè abbiano altro +ufizio nella generazione degl' insetti, se non d'apprestare un luogo o un +nido proporzionato, in cui dagli animali nel tempo della figliatura sieno +portati, e partoriti i vermi, o l' uova o l' altre semenze dei vermi, i +quali tosto che nati sono, trovano in esso nido un sufficiente alimento +abilissimo per nutricarsi: e se in quello non son portate dalle madri +queste suddette semenze, niente mai, e replicatamente niente, vi s' +ingegneri e nasca."--REDI, _Esperienze_, pp. 14-16.] + +In the seventeenth century, as I have said, the latter was the dominant +view, sanctioned alike by antiquity and by authority; and it is +interesting to observe that Redi did not escape the customary tax upon a +discoverer of having to defend himself against the charge of impugning +the authority of the Scriptures;[5] for his adversaries declared that the +generation of bees from the carcase of a dead lion is affirmed, in the +Book of Judges, to have been the origin of the famous riddle with which +Samson perplexed the Philistines:-- + +Out of the eater came forth meat, +And out of the strong came forth sweetness. + +[Footnote 5: "Molti, e molti altri ancora vi potrei annoverare, se non +fossi chiamato a rispondere alle rampogne di alcuni, che bruscamente mi +rammentano ciò, che si legge nel capitolo quattordicesimo del sacrosanto +Libro de' giudici ... "--REDI, _loc. cit._ p. 45.] + +Against all odds, however, Redi, strong with the strength of demonstrable +fact, did splendid battle for Biogenesis; but it is remarkable that he +held the doctrine in a sense which, if he lead lived in these times, +would have infallibly caused him to be classed among the defenders of +"spontaneous generation." "Omne vivum ex vivo," "no life without +antecedent life," aphoristically sums up Redi's doctrine; but he went no +further. It is most remarkable evidence of the philosophic caution and +impartiality of his mind, that although he had speculatively anticipated +the manner in which grubs really are deposited in fruits and in the galls +of plants, he deliberately admits that the evidence is insufficient to +bear him out; and he therefore prefers the supposition that they are +generated by a modification of the living substance of the plants +themselves. Indeed, he regards these vegetable growths as organs, by +means of which the plant gives rise to an animal, and looks upon this +production of specific animals as the final cause of the galls and of, at +any rate, some fruits. And he proposes to explain the occurrence of +parasites within the animal body in the same way.[6] + +[Footnote 6: The passage (_Esperienze_, p. 129) is worth quoting in +full:-- + +"Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi, +gli alberi e le foglie, in due maniere inverminassero. Una, perchè +venendo i bachi per dí fuora, e cercando l' alimento, col rodere ci +aprono la strada, ed arrivano alla più interna midolla de' frutti e de' +legni. L'altra maniera si è, che io per me stimerei, che non fosse gran +fatto disdicevole il credere, che quell' anima o quella virtù, la quale +genera i fiori ed i frutti nelle piante viventi, sia quella stessa che +generi ancora i bachi di esse piante. E chi sà, forse, che molti frutti +degli alberi non sieno prodotti, non per un fine primario e principale, +ma bensi per un uffizio secondario e servile, destinato alla generazione +di que' vermi, servendo a loro in vece di matrice, in cui dimorino un +prefisso e determinato tempo; il quale arrivato escan fuora a godere il +sole. + +"Io m' immagino, che questo mio pensiero non vi parrà totalmento un +paradosso; mentro farete riflessione a quelle tanto sorte di galle, di +gallozzole, di coccole, di ricci, di calici, di cornetti ed i lappole, +che son produtte dalle quercel, dalle farnie, da' cerri, da' sugheri, da' +leeci e da altri simili alberi de ghianda; imperciocchè in quello +gallozzole, e particolarmente nelle più grosse, che si chiamano coronati, +ne' ricci capelluti, che ciuffoli da' nostri contadini son detti; nei +ricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzze +della foglia del leccio si vede evidentissimamente, che la prima e +principale intenzione della natura è formare dentro di quelle un animale +volante; vedendosi nel centro della gallozzola un uovo, che col crescere +e col maturarsi di essa gallozzola va crescendo e maturando anch' egli, e +cresce altresi a suo tempo quel verme, che nell' uovo si racchiude; il +qual verme, quando la gallozzola è finita di maturare e che è venuto il +termine destinato al suo nascimento, diventa, di verme che era, una +mosca.... Io vi confesso ingenuamente, che prima d'aver fatte queste mie +esperienze intorno alla generazione degl' insetti mi dava a credere, o +per dir meglio sospettava, che forse la gallozzola nascesse, perchè +arrivando la mosca nel tempo della primavera, e facendo una piccolissima +fessura ne' rami più teneri della quercia, in quella fessura nascondesse +uno de suoi semi, il quale fosse cagione che sbocciasse fuora la +gallozzola; e che mai non si vedessero galle o gallozzole o ricci o +cornetti o calici o coccole, se non in que' rami, ne' quali le mosche +avessero depositate le loro semenze; e mi dava ad intendere, che le +gallozzole fossero una malattia cagionata nelle querce dalle punture +delle mosche, in quella giusa stessa che dalle punture d'altri animaletti +simiglievoli veggiamo crescere de' tumori ne' corpi degli animali."] + +It is of great importance to apprehend Redi's position rightly; for the +lines of thought he laid down for us are those upon which naturalists +have been working ever since. Clearly, he held _Biogenesis_ as against +_Abiogenesis;_ and I shall immediately proceed, in the first place, to +inquire how far subsequent investigation has borne him out in so doing. + +But Redi also thought that there were two modes of Biogenesis. By the one +method, which is that of common and ordinary occurrence, the living +parent gives rise to offspring which passes through the same cycle of +changes as itself--like gives rise to like; and this has been termed +_Homogenesis_. By the other mode, the living parent was supposed to give +rise to offspring which passed through a totally different series of +states from those exhibited by the parent, and did not return into the +cycle of the parent; this is what ought to be called _Heterogenesis_, the +offspring being altogether, and permanently, unlike the parent. The term +Heterogenesis, however, has unfortunately been used in a different sense, +and M. Milne-Edwards has therefore substituted for it _Xenogenesis_, +which means the generation of something foreign. After discussing Redi's +hypothesis of universal Biogenesis, then, I shall go on to ask how far +the growth of science justifies his other hypothesis of Xenogenesis. + +The progress of the hypothesis of Biogenesis was triumphant and unchecked +for nearly a century. The application of the microscope to anatomy in the +hands of Grew, Leeuwenhoek, Swammerdam, Lyonnet, Vallisnieri, Réaurnur, +and other illustrious investigators of nature of that day, displayed such +a complexity of organisation in the lowest and minutest forms, and +everywhere revealed such a prodigality of provision for their +multiplication by germs of one sort or another, that the hypothesis of +Abiogenesis began to appear not only untrue, but absurd; and, in the +middle of the eighteenth century, when Needham and Buffon took up the +question, it was almost universally discredited.[7] + +[Footnote 7: Needham, writing in 1750, says:-- + +"Les naturalistes modernes s'accordent unaninement à établir, comme une +vérité certaine, que toute plante vient do sa sémence spécifique, tout +animal d'un oeuf ou de quelque chose d'analogue préexistant dans la +plante, ou dans l'animal de même espèce qui l'a produit."--_Nouvelles +Observations_, p. 169. + +"Les naturalistes out généralemente cru que les animaux microscopiques +étaient engendrés par des oeufs transportés dans l'air, ou déposés dans +des eaux dormantes par des insectes volans."--_Ibid._ p. 176.] + +But the skill of the microscope makers of the eighteenth century soon +reached its limit. A microscope magnifying 400 diameters was a _chef +d'oeuvre_ of the opticians of that day; and, at the same time, by no +means trustworthy. But a magnifying power of 400 diameters, even when +definition reaches the exquisite perfection of our modern achromatic +lenses, hardly suffices for the mere discernment of the smallest forms of +life. A speck, only 1/25th of an inch in diameter, has, at ten inches +from the eye, the same apparent size as an object 1/10000th of an inch in +diameter, when magnified 400 times; but forms of living matter abound, +the diameter of which is not more than 1/40000th of an inch. A filtered +infusion of hay, allowed to stand for two days, will swarm with living +things among which, any which reaches the diameter of a human red blood- +corpuscle, or about 1/3200th of an inch, is a giant. It is only by +bearing these facts in mind, that we can deal fairly with the remarkable +statements and speculations put forward by Buffon and Needham in the +middle of the eighteenth century. + +When a portion of any animal or vegetable body is infused in water, it +gradually softens and disintegrates; and, as it does so, the water is +found to swarm with minute active creatures, the so-called Infusorial +Animalcules, none of which can be seen, except by the aid of the +microscope; while a large proportion belong to the category of smallest +things of which I have spoken, and which must have looked like mere dots +and lines under the ordinary microscopes of the eighteenth century. + +Led by various theoretical considerations which I cannot now discuss, but +which looked promising enough in the lights of their time, Buffon and +Needham doubted the applicability of Redi's hypothesis to the infusorial +animalcules, and Needham very properly endeavoured to put the question to +an experimental test. He said to himself, If these infusorial animalcules +come from germs, their germs must exist either in the substance infused, +or in the water with which the infusion is made, or in the superjacent +air. Now the vitality of all germs is destroyed by heat. Therefore, if I +boil the infusion, cork it up carefully, cementing the cork over with +mastic, and then heat the whole vessel by heaping hot ashes over it, I +must needs kill whatever germs are present. Consequently, if Redi's +hypothesis hold good, when the infusion is taken away and allowed to +cool, no animalcules ought to be developed in it; whereas, if the +animalcules are not dependent on pre-existing germs, but are generated +from the infused substance, they ought, by and by, to make their +appearance. Needham found that, under the circumstances in which he made +his experiments, animalcules always did arise in the infusions, when a +sufficient time had elapsed to allow for their development. + +In much of his work Needham was associated with Buffon, and the results +of their experiments fitted in admirably with the great French +naturalist's hypothesis of "organic molecules," according to which, life +is the indefeasible property of certain indestructible molecules of +matter, which exist in all living things, and have inherent activities by +which they are distinguished from not living matter. Each individual +living organism is formed by their temporary combination. They stand to +it in the relation of the particles of water to a cascade, or a +whirlpool; or to a mould, into which the water is poured. The form of the +organism is thus determined by the reaction between external conditions +and the inherent activities of the organic molecules of which it is +composed; and, as the stoppage of a whirlpool destroys nothing but a +form, and leaves the molecules of the water, with all their inherent +activities intact, so what we call the death and putrefaction of an +animal, or of a plant, is merely the breaking up of the form, or manner +of association, of its constituent organic molecules, which are then set +free as infusorial animalcules. + +It will be perceived that this doctrine is by no means identical with +_Abiogenesis_, with which it is often confounded. On this hypothesis, a +piece of beef, or a handful of hay, is dead only in a limited sense. The +beef is dead ox, and the hay is dead grass; but the "organic molecules" +of the beef or the hay are not dead, but are ready to manifest their +vitality as soon as the bovine or herbaceous shrouds in which they are +imprisoned are rent by the macerating action of water. The hypothesis +therefore must be classified under Xenogenesis, rather than under +Abiogenesis. Such as it was, I think it will appear, to those who will be +just enough to remember that it was propounded before the birth of modern +chemistry, and of the modern optical arts, to be a most ingenious and +suggestive speculation. + +But the great tragedy of Science--the slaying of a beautiful hypothesis +by an ugly fact--which is so constantly being enacted under the eyes of +philosophers, was played, almost immediately, for the benefit of Buffon +and Needham. + +Once more, an Italian, the Abbé Spallanzani, a worthy successor and +representative of Redi in his acuteness, his ingenuity, and his learning, +subjected the experiments and the conclusions of Needham to a searching +criticism. It might be true that Needham's experiments yielded results +such as he had described, but did they bear out his arguments? Was it not +possible, in the first place, he had not completely excluded the air by +his corks and mastic? And was it not possible, in the second place, that +he had not sufficiently heated his infusions and the superjacent air? +Spallanzani joined issue with the English naturalist on both these pleas, +and he showed that if, in the first place, the glass vessels in which the +infusions were contained were hermetically sealed by fusing their necks, +and if, in the second place, they were exposed to the temperature of +boiling water for three-quarters of an hour,[8] no animalcules ever made +their appearance within them. It must be admitted that the experiments +and arguments of Spallanzani furnish a complete and a crushing reply to +those of Needham. But we all too often forget that it is one thing to +refute a proposition, and another to prove the truth of a doctrine which, +implicitly or explicitly, contradicts that proposition; and the advance +of science soon showed that though Needham might be quite wrong, it did +not follow that Spallanzani was quite right. + +[Footnote 8: See Spallanzani, _Opere_, vi. pp. 42 and 51.] + +Modern Chemistry, the birth of the latter half of the eighteenth century, +grew apace, and soon found herself face to face with the great problems +which biology had vainly tried to attack without her help. The discovery +of oxygen led to the laying of the foundations of a scientific theory of +respiration, and to an examination of the marvellous interactions of +organic substances with oxygen. The presence of free oxygen appeared to +be one of the conditions of the existence of life, and of those singular +changes in organic matters which are known as fermentation and +putrefaction. The question of the generation of the infusory animalcules +thus passed into a new phase. For what might not have happened to the +organic matter of the infusions, or to the oxygen of the air, in +Spallanzani's experiments? What security was there that the development +of life which ought to have taken place had not been checked or prevented +by these changes? + +The battle had to be fought again. It was needful to repeat the +experiments under conditions which would make sure that neither the +oxygen of the air, nor the composition of the organic matter, was altered +in such a manner as to interfere with the existence of life. + +Schulze and Schwann took up the question from this point of view in 1836 +and 1837. The passage of air through red-hot glass tubes, or through +strong sulphuric acid, does not alter the proportion of its oxygen, while +it must needs arrest, or destroy, any organic matter which may be +contained in the air. These experimenters, therefore, contrived +arrangements by which the only air which should come into contact with a +boiled infusion should be such as had either passed through red-hot tubes +or through strong sulphuric acid. The result which they obtained was that +an infusion so treated developed no living things, while, if the same +infusion was afterwards exposed to the air, such things appeared rapidly +and abundantly. The accuracy of these experiments has been alternately +denied and affirmed. Supposing then, to be accepted, however, all that +they really proved was that the treatment to which the air was subjected +destroyed _something_ that was essential to the development of life in +the infusion. This "something" might be gaseous, fluid, or solid; that it +consisted of germs remained only an hypothesis of greater or less +probability. + +Contemporaneously with these investigations a remarkable discovery was +made by Cagniard de la Tour. He found that common yeast is composed of a +vast accumulation of minute plants. The fermentation of must, or of wort, +in the fabrication of wine and of beer, is always accompanied by the +rapid growth and multiplication of these _Toruloe_. Thus, fermentation, +in so far as it was accompanied by the development of microscopical +organisms in enormous numbers, became assimilated to the decomposition of +an infusion of ordinary animal or vegetable matter; and it was an obvious +suggestion that the organisms were, in some way or other, the causes both +of fermentation and of putrefaction. The chemists, with Berzelius and +Liebig at their head, at first laughed this idea to scorn; but in 1843, a +man then very young, who has since performed the unexampled feat of +attaining to high eminence alike in Mathematics, Physics, and Physiology-- +I speak of the illustrious Helmholtz--reduced the matter to the test of +experiment by a method alike elegant and conclusive. Helmholtz separated +a putrefying or a fermenting liquid from one which was simply putrescible +or fermentable by a membrane which allowed the fluids to pass through and +become intermixed, but stopped the passage of solids. The result was, +that while the putrescible or the fermentable liquids became impregnated +with the results of the putrescence or fermentation which was going on on +the other side of the membrane, they neither putrefied (in the ordinary +way) nor fermented; nor were any of the organisms which abounded in the +fermenting or putrefying liquid generated in them. Therefore the cause of +the development of these organisms must lie in something which cannot +pass through membranes; and as Helmholtz's investigations were long +antecedent to Graham's researches upon colloids, his natural conclusion +was that the agent thus intercepted must be a solid material. In point of +fact, Helmholtz's experiments narrowed the issue to this: that which +excites fermentation and putrefaction, and at the same time gives rise to +living forms in a fermentable or putrescible fluid, is not a gas and is +not a diffusible fluid; therefore it is either a colloid, or it is matter +divided into very minute solid particles. + +The researches of Schroeder and Dusch in 1854, and of Schroeder alone, in +1859, cleared up this point by experiments which are simply refinements +upon those of Redi. A lump of cotton-wool is, physically speaking, a pile +of many thicknesses of a very fine gauze, the fineness of the meshes of +which depends upon the closeness of the compression of the wool. Now, +Schroeder and Dusch found, that, in the case of all the putrefiable +materials which they used (except milk and yolk of egg), an infusion +boiled, and then allowed to come into contact with no air but such as had +been filtered through cotton-wool, neither putrefied, nor fermented, nor +developed living forms. It is hard to imagine what the fine sieve formed +by the cotton-wool could have stopped except minute solid particles. +Still the evidence was incomplete until it had been positively shown, +first, that ordinary air does contain such particles; and, secondly, that +filtration through cotton-wool arrests these particles and allows only +physically pure air to pass. This demonstration has been furnished within +the last year by the remarkable experiments of Professor Tyndall. It has +been a common objection of Abiogenists that, if the doctrine of Biogeny +is true, the air must be thick with germs; and they regard this as the +height of absurdity. But nature occasionally is exceedingly unreasonable, +and Professor Tyndall has proved that this particular absurdity may +nevertheless be a reality. He has demonstrated that ordinary air is no +better than a sort of stirabout of excessively minute solid particles; +that these particles are almost wholly destructible by heat; and that +they are strained off, and the air rendered optically pure, by its being +passed through cotton-wool. + +It remains yet in the order of logic, though not of history, to show that +among these solid destructible particles, there really do exist germs +capable of giving rise to the development of living forms in suitable +menstrua. This piece of work was done by M. Pasteur in those beautiful +researches which will ever render his name famous; and which, in spite of +all attacks upon them, appear to me now, as they did seven years ago,[9] +to be models of accurate experimentation and logical reasoning. He +strained air through cotton-wool, and found, as Schroeder and Dusch had +done, that it contained nothing competent to give rise to the development +of life in fluids highly fitted for that purpose. But the important +further links in the chain of evidence added by Pasteur are three. In the +first place he subjected to microscopic examination the cotton-wool which +had served as strainer, and found that sundry bodies clearly recognisable +as germs, were among the solid particles strained off. Secondly, he +proved that these germs were competent to give rise to living forms by +simply sowing them in a solution fitted for their development. And, +thirdly, he showed that the incapacity of air strained through cotton- +wool to give rise to life, was not due to any occult change effected in +the constituents of the air by the wool, by proving that the cotton-wool +might be dispensed with altogether, and perfectly free access left +between the exterior air and that in the experimental flask. If the neck +of the flask is drawn out into a tube and bent downwards; and if, after +the contained fluid has been carefully boiled, the tube is heated +sufficiently to destroy any germs which may be present in the air which +enters as the fluid cools, the apparatus may be left to itself for any +time and no life will appear in the fluid. The reason is plain. Although +there is free communication between the atmosphere laden with germs and +the germless air in the flask, contact between the two takes place only +in the tube; and as the germs cannot fall upwards, and there are no +currents, they never reach the interior of the flask. But if the tube be +broken short off where it proceeds from the flask, and free access be +thus given to germs falling vertically out of the air, the fluid, which +has remained clear and desert for months, becomes, in a few days, turbid +and full of life. + +[Footnote 9: _Lectures to Working Men on the Causes of the Phenomena of +Organic Nature_, 1863. (See Vol. II. of these Essays.)] + +These experiments have been repeated over and over again by independent +observers with entire success; and there is one very simple mode of +seeing the facts for one's self, which I may as well describe. + +Prepare a solution (much used by M. Pasteur, and often called "Pasteur's +solution") composed of water with tartrate of ammonia, sugar, and yeast- +ash dissolved therein.[10] Divide it into three portions in as many +flasks; boil all three for a quarter of an hour; and, while the steam is +passing out, stop the neck of one with a large plug of cotton-wool, so +that this also may be thoroughly steamed. Now set the flasks aside to +cool, and, when their contents are cold, add to one of the open ones a +drop of filtered infusion of hay which has stood for twenty-four hours, +and is consequently hill of the active and excessively minute organisms +known as _Bacteria_. In a couple of days of ordinary warm weather the +contents of this flask will be milky from the enormous multiplication of +_Bacteria_. The other flask, open and exposed to the air, will, sooner or +later, become milky with _Bacteria_, and patches of mould may appear in +it; while the liquid in the flask, the neck of which is plugged with +cotton-wool, will remain clear for an indefinite time. I have sought in +vain for any explanation of these facts, except the obvious one, that the +air contains germs competent to give rise to _Bacteria_, such as those +with which the first solution has been knowingly and purposely +inoculated, and to the mould-_Fungi_. And I have not yet been able to +meet with any advocate of Abiogenesis who seriously maintains that the +atoms of sugar, tartrate of ammonia, yeast-ash, and water, under no +influence but that of free access of air and the ordinary temperature, +re-arrange themselves and give rise to the protoplasm of _Bacterium_. But +the alternative is to admit that these _Bacteria_ arise from germs in the +air; and if they are thus propagated, the burden of proof that other like +forms are generated in a different manner, must rest with the assertor of +that proposition. + +[Footnote 10: Infusion of hay treated in the same way yields similar +results; but as it contains organic matter, the argument which follows +cannot be based upon it.] + +To sum up the effect of this long chain of evidence:-- + +It is demonstrable that a fluid eminently fit for the development of the +lowest forms of life, but which contains neither germs, nor any protein +compound, gives rise to living things in great abundance if it is exposed +to ordinary air; while no such development takes place, if the air with +which it is in contact is mechanically freed from the solid particles +which ordinarily float in it, and which may be made visible by +appropriate means. + +It is demonstrable that the great majority of these particles are +destructible by heat, and that some of them are germs, or living +particles, capable of giving rise to the same forms of life as those +which appear when the fluid is exposed to unpurified air. + +It is demonstrable that inoculation of the experimental fluid with a drop +of liquid known to contain living particles gives rise to the same +phenomena as exposure to unpurified air. + +And it is further certain that these living particles are so minute that +the assumption of their suspension in ordinary air presents not the +slightest difficulty. On the contrary, considering their lightness and +the wide diffusion of the organisms which produce them, it is impossible +to conceive that they should not be suspended in the atmosphere in +myriads. + +Thus the evidence, direct and indirect, in favour of _Biogenesis_ for all +known forms of life must, I think, be admitted to be of great weight. + +On the other side, the sole assertions worthy of attention are that +hermetically sealed fluids, which have been exposed to great and long- +continued heat, have sometimes exhibited living forms of low organisation +when they have been opened. + +The first reply that suggests itself is the probability that there must +be some error about these experiments, because they are performed on an +enormous scale every day with quite contrary results. Meat, fruits, +vegetables, the very materials of the most fermentable and putrescible +infusions, are preserved to the extent, I suppose I may say, of thousands +of tons every year, by a method which is a mere application of +Spallanzani's experiment. The matters to be preserved are well boiled in +a tin case provided with a small hole, and this hole is soldered up when +all the air in the case has been replaced by steam. By this method they +may be kept for years without putrefying, fermenting, or getting mouldy. +Now this is not because oxygen is excluded, inasmuch as it is now proved +that free oxygen is not necessary for either fermentation or +putrefaction. It is not because the tins are exhausted of air, for +_Vibriones_ and _Bacteria_ live, as Pasteur has shown, without air or +free oxygen. It is not because the boiled meats or vegetables are not +putrescible or fermentable, as those who have had the misfortune to be in +a ship supplied with unskilfully closed tins well know. What is it, +therefore, but the exclusion of germs? I think that Abiogenists are bound +to answer this question before they ask us to consider new experiments of +precisely the same order. + +And in the next place, if the results of the experiments I refer to are +really trustworthy, it by no means follows that Abiogenesis has taken +place. The resistance of living matter to heat is known to vary within +considerable limits, and to depend, to some extent, upon the chemical and +physical qualities of the surrounding medium. But if, in the present +state of science, the alternative is offered us,--either germs can stand +a greater heat than has been supposed, or the molecules of dead matter, +for no valid or intelligible reason that is assigned, are able to re- +arrange themselves into living bodies, exactly such as can be +demonstrated to be frequently produced in another way,--I cannot +understand how choice can be, even for a moment, doubtful. + +But though I cannot express this conviction of mine too strongly, I must +carefully guard myself against the supposition that I intend to suggest +that no such thing as Abiogenesis ever has taken place in the past, or +ever will take place in the future. With organic chemistry, molecular +physics, and physiology yet in their infancy, and every day making +prodigious strides, I think it would be the height of presumption for any +man to say that the conditions under which matter assumes the properties +we call "vital" may not, some day, be artificially brought together. All +I feel justified in affirming is, that I see no reason for believing that +the feat has been performed yet. + +And looking back through the prodigious vista of the past, I find no +record of the commencement of life, and therefore I am devoid of any +means of forming a definite conclusion as to the conditions of its +appearance. Belief, in the scientific sense of the word, is a serious +matter, and needs strong foundations. To say, therefore, in the admitted +absence of evidence, that I have any belief as to the mode in which the +existing forms of life have originated, would be using words in a wrong +sense. But expectation is permissible where belief is not; and if it were +given me to look beyond the abyss of geologically recorded time to the +still more remote period when the earth was passing through physical and +chemical conditions, which it can no more see again than a man can recall +his infancy, I should expect to be a witness of the evolution of living +protoplasm from not living matter. I should expect to see it appear under +forms of great simplicity, endowed, like existing fungi, with the power +of determining the formation of new protoplasm from such matters as +ammonium carbonates, oxalates and tartrates, alkaline and earthy +phosphates, and water, without the aid of light. That is the expectation +to which analogical reasoning leads me; but I beg you once more to +recollect that I have no right to call my opinion anything but an act of +philosophical faith. + +So much for the history of the progress of Redi's great doctrine of +Biogenesis, which appears to me, with the limitations I have expressed, +to be victorious along the whole line at the present day. + +As regards the second problem offered to us by Redi, whether Xenogenesis +obtains, side by side with Homogenesis,--whether, that is, there exist +not only the ordinary living things, giving rise to offspring which run +through the same cycle as themselves, but also others, producing +offspring which are of a totally different character from themselves,-- +the researches of two centuries have led to a different result. That the +grubs found in galls are no product of the plants on which the galls +grow, but are the result of the introduction of the eggs of insects into +the substance of these plants, was made out by Vallisnieri, Réaumur, and +others, before the end of the first half of the eighteenth century. The +tapeworms, bladderworms, and flukes continued to be a stronghold of the +advocates of Xenogenesis for a much longer period. Indeed, it is only +within the last thirty years that the splendid patience of Von Siebold, +Van Beneden, Leuckart, Küchenmeister, and other helminthologists, has +succeeded in tracing every such parasite, often through the strangest +wanderings and metamorphoses, to an egg derived from a parent, actually +or potentially like itself; and the tendency of inquiries elsewhere has +all been in the same direction. A plant may throw off bulbs, but these, +sooner or later, give rise to seeds or spores, which develop into the +original form. A polype may give rise to Medusae, or a pluteus to an +Echinoderm, but the Medusa and the Echinoderm give rise to eggs which +produce polypes or glutei, and they are therefore only stages in the +cycle of life of the species. + +But if we turn to pathology, it offers us some remarkable approximations +to true Xenogenesis. + +As I have already mentioned, it has been known since the time of +Vallisnieri and of Réaumur, that galls in plants, and tumours in cattle, +are caused by insects, which lay their eggs in those parts of the animal +or vegetable frame of which these morbid structures are outgrowths. +Again, it is a matter of familiar experience to everybody that mere +pressure on the skin will give rise to a corn. Now the gall, the tumour, +and the corn are parts of the living body, which have become, to a +certain degree, independent and distinct organisms. Under the influence +of certain external conditions, elements of the body, which should have +developed in due subordination to its general plan, set up for themselves +and apply the nourishment which they receive to their own purposes. + +From such innocent productions as corns and warts, there are all +gradations to the serious tumours which, by their mere size and the +mechanical obstruction they cause, destroy the organism out of which they +are developed; while, finally, in those terrible structures known as +cancers, the abnormal growth has acquired powers of reproduction and +multiplication, and is only morphologically distinguishable from the +parasitic worm, the life of which is neither more nor less closely bound +up with that of the infested organism. + +If there were a kind of diseased structure, the histological elements of +which were capable of maintaining a separate and independent existence +out of the body, it seems to me that the shadowy boundary between morbid +growth and Xenogenesis would be effaced. And I am inclined to think that +the progress of discovery has almost brought us to this point already. I +have been favoured by Mr. Simon with an early copy of the last published +of the valuable "Reports on the Public Health," which, in his capacity of +their medical officer, he annually presents to the Lords of the Privy +Council. The appendix to this report contains an introductory essay "On +the Intimate Pathology of Contagion," by Dr. Burdon-Sanderson, which is +one of the clearest, most comprehensive, and well-reasoned discussions of +a great question which has come under my notice for a long time. I refer +you to it for details and for the authorities for the statements I am +about to make. + +You are familiar with what happens in vaccination. A minute cut is made +in the skin, and an infinitesimal quantity of vaccine matter is inserted +into the wound. Within a certain time a vesicle appears in the place of +the wound, and the fluid which distends this vesicle is vaccine matter, +in quantity a hundred or a thousandfold that which was originally +inserted. Now what has taken place in the course of this operation? Has +the vaccine matter, by its irritative property, produced a mere blister, +the fluid of which has the same irritative property? Or does the vaccine +matter contain living particles, which have grown and multiplied where +they have been planted? The observations of M. Chauveau, extended and +confirmed by Dr. Sanderson himself, appear to leave no doubt upon this +head. Experiments, similar in principle to those of Helmholtz on +fermentation and putrefaction, have proved that the active element in the +vaccine lymph is non-diffusible, and consists of minute particles not +exceeding 1/20000th of an inch in diameter, which are made visible in the +lymph by the microscope. Similar experiments have proved that two of the +most destructive of epizootic diseases, sheep-pox and glanders, are also +dependent for their existence and their propagation upon extremely small +living solid particles, to which the title of _microzymes_ is applied. An +animal suffering under either of these terrible diseases is a source of +infection and contagion to others, for precisely the same reason as a tub +of fermenting beer is capable of propagating its fermentation by +"infection," or "contagion," to fresh wort. In both cases it is the solid +living particles which are efficient; the liquid in which they float, and +at the expense of which they live, being altogether passive. + +Now arises the question, are these microzymes the results of +_Homogenesis_, or of _Xenogenesis?_ are they capable, like the +_Toruloe_ of yeast, of arising only by the development of pre-existing +germs? or may they be, like the constituents of a nut-gall, the results +of a modification and individualisation of the tissues of the body in +which they are found, resulting from the operation of certain conditions? +Are they parasites in the zoological sense, or are they merely what +Virchow has called "heterologous growths"? It is obvious that this +question has the most profound importance, whether we look at it from a +practical or from a theoretical point of view. A parasite may be stamped +out by destroying its germs, but a pathological product can only be +annihilated by removing the conditions which give rise to it. + +It appears to me that this great problem will have to be solved for each +zymotic disease separately, for analogy cuts two ways. I have dwelt upon +the analogy of pathological modification, which is in favour of the +xenogenetic origin of microzymes; but I must now speak of the equally +strong analogies in favour of the origin of such pestiferous particles by +the ordinary process of the generation of like from like. + +It is, at present, a well-established fact that certain diseases, both of +plants and of animals, which have all the characters of contagious and +infectious epidemics, are caused by minute organisms. The smut of wheat +is a well-known instance of such a disease, and it cannot be doubted that +the grape-disease and the potato-disease fall under the same category. +Among animals, insects are wonderfully liable to the ravages of +contagious and infectious diseases caused by microscopic _Fungi_. + +In autumn, it is not uncommon to see flies motionless upon a window-pane, +with a sort of magic circle, in white, drawn round them. On microscopic +examination, the magic circle is found to consist of innumerable spores, +which have been thrown off in all directions by a minute fungus called +_Empusa muscoe_, the spore-forming filaments of which stand out like a +pile of velvet from the body of the fly. These spore-forming filaments +are connected with others which fill the interior of the fly's body like +so much fine wool, having eaten away and destroyed the creature's +viscera. This is the full-grown condition of the _Empusa_. If traced back +to its earliest stages, in flies which are still active, and to all +appearance healthy, it is found to exist in the form of minute corpuscles +which float in the blood of the fly. These multiply and lengthen into +filaments, at the expense of the fly's substance; and when they have at +last killed the patient, they grow out of its body and give off spores. +Healthy flies shut up with diseased ones catch this mortal disease, and +perish like the others. A most competent observer, M. Cohn, who studied +the development of the _Empusa_ very carefully, was utterly unable to +discover in what manner the smallest germs of the _Empusa_ got into the +fly. The spores could not be made to give rise to such germs by +cultivation; nor were such germs discoverable in the air, or in the food +of the fly. It looked exceedingly like a case of Abiogenesis, or, at any +rate, of Xenogenesis; and it is only quite recently that the real course +of events has been made out. It has been ascertained, that when one of +the spores falls upon the body of a fly, it begins to germinate, and +sends out a process which bores its way through the fly's skin; this, +having reached the interior cavities of its body, gives off the minute +floating corpuscles which are the earliest stage of the _Empusa_. The +disease is "contagious," because a healthy fly coming in contact with a +diseased one, from which the spore-bearing filaments protrude, is pretty +sure to carry off a spore or two. It is "infectious" because the spores +become scattered about all sorts of matter in the neighbourhood of the +slain flies. + +The silkworm has long been known to be subject to a very fatal and +infectious disease called the _Muscardine_. Audouin transmitted it by +inoculation. This disease is entirely due to the development of a fungus, +_Botrytis Bassiana_, in the body of the caterpillar; and its +contagiousness and infectiousness are accounted for in the same way as +those of the fly-disease. But, of late years, a still more serious +epizootic has appeared among the silkworms; and I may mention a few facts +which will give you some conception of the gravity of the injury which it +has inflicted on France alone. + +The production of silk has been for centuries an important branch of +industry in Southern France, and in the year 1853 it had attained such a +magnitude that the annual produce of the French sericulture was estimated +to amount to a tenth of that of the whole world, and represented a money- +value of 117,000,000 francs, or nearly five millions sterling. What may +be the sum which would represent the money-value of all the industries +connected with the working up of the raw silk thus produced, is more than +I can pretend to estimate. Suffice it to say, that the city of Lyons is +built upon French silk as much as Manchester was upon American cotton +before the civil war. + +Silkworms are liable to many diseases; and, even before 1853, a peculiar +epizootic, frequently accompanied by the appearance of dark spots upon +the skin (whence the name of "Pébrine" which it has received), had been +noted for its mortality. But in the years following 1853 this malady +broke out with such extreme violence, that, in 1858, the silk-crop was +reduced to a third of the amount which it had reached in 1853; and, up +till within the last year or two, it has never attained half the yield of +1853. This means not only that the great number of people engaged in silk +growing are some thirty millions sterling poorer than they might have +been; it means not only that high prices have had to be paid for imported +silkworm eggs, and that, after investing his money in them, in paying for +mulberry-leaves and for attendance, the cultivator has constantly seen +his silkworms perish and himself plunged in ruin; but it means that the +looms of Lyons have lacked employment, and that, for years, enforced +idleness and misery have been the portion of a vast population which, in +former days, was industrious and well-to-do. + +In 1858 the gravity of the situation caused the French Academy of +Sciences to appoint Commissioners, of whom a distinguished naturalist, M. +de Quatrefages, was one, to inquire into the nature of this disease, and, +if possible, to devise some means of staying the plague. In reading the +Report[11] made by M. de Quatrefages in 1859, it is exceedingly +interesting to observe that his elaborate study of the Pébrine forced the +conviction upon his mind that, in its mode of occurrence and propagation, +the disease of the silkworm is, in every respect, comparable to the +cholera among mankind. But it differs from the cholera, and so far is a +more formidable malady, in being hereditary, and in being, under some +circumstances, contagious as well as infectious. + +[Footnote 11: _Études sur les Maladies actuelles des Vers à Soie_, p. +53.] + +The Italian naturalist, Filippi, discovered in the blood of the silkworms +affected by this strange disorder a multitude of cylindrical corpuscles, +each about 1/6000th of an inch long. These have been carefully studied by +Lebert, and named by him _Panhistophyton_; for the reason that in +subjects in which the disease is strongly developed, the corpuscles swarm +in every tissue and organ of the body, and even pass into the undeveloped +eggs of the female moth. But are these corpuscles causes, or mere +concomitants, of the disease? Some naturalists took one view and some +another; and it was not until the French Government, alarmed by the +continued ravages of the malady, and the inefficiency of the remedies +which had been suggested, despatched M. Pasteur to study it, that the +question received its final settlement; at a great sacrifice, not only of +the time and peace of mind of that eminent philosopher, but, I regret to +have to add, of his health. + +But the sacrifice has not been in vain. It is now certain that this +devastating, cholera-like, Pébrine, is the effect of the growth and +multiplication of the _Panhistophyton_ in the silkworm. It is contagious +and infectious, because the corpuscles of the _Panhistophyton_ pass away +from the bodies of the diseased caterpillars, directly or indirectly, to +the alimentary canal of healthy silkworms in their neighbourhood; it is +hereditary because the corpuscles enter into the eggs while they are +being formed, and consequently are carried within them when they are +laid; and for this reason, also, it presents the very singular +peculiarity of being inherited only on the mother's side. There is not a +single one of all the apparently capricious and unaccountable phenomena +presented by the Pébrine, but has received its explanation from the fact +that the disease is the result of the presence of the microscopic +organism, _Panhistophyton_. + +Such being the facts with respect to the Pébrine, what are the +indications as to the method of preventing it? It is obvious that this +depends upon the way in which the _Panhistophyton_ is generated. If it +may be generated by Abiogenesis, or by Xenogenesis, within the silkworm +or its moth, the extirpation of the disease must depend upon the +prevention of the occurrence of the conditions under which this +generation takes place. But if, on the other hand, the _Panhistophyton_ +is an independent organism, which is no more generated by the silkworm +than the mistletoe is generated by the apple-tree or the oak on which it +grows, though it may need the silkworm for its development in the same +way as the mistletoe needs the tree, then the indications are totally +different. The sole thing to be done is to get rid of and keep away the +germs of the _Panhistophyton_. As might be imagined, from the course of +his previous investigations, M. Pasteur was led to believe that the +latter was the right theory; and, guided by that theory, he has devised a +method of extirpating the disease, which has proved to be completely +successful wherever it has been properly carried out. + +There can be no reason, then, for doubting that, among insects, +contagious and infectious diseases, of great malignity, are caused by +minute organisms which are produced from pre-existing germs, or by +homogenesis; and there is no reason, that I know of, for believing that +what happens in insects may not take place in the highest animals. +Indeed, there is already strong evidence that some diseases of an +extremely malignant and fatal character to which man is subject, are as +much the work of minute organisms as is the Pébrine. I refer for this +evidence to the very striking facts adduced by Professor Lister in his +various well-known publications on the antiseptic method of treatment. It +appears to me impossible to rise from the perusal of those publications +without a strong conviction that the lamentable mortality which so +frequently dogs the footsteps of the most skilful operator, and those +deadly consequences of wounds and injuries which seem to haunt the very +walls of great hospitals, and are, even now, destroying more men than die +of bullet or bayonet, are due to the importation of minute organisms into +wounds, and their increase and multiplication; and that the surgeon who +saves most lives will be he who best works out the practical consequences +of the hypothesis of Redi. + +I commenced this Address by asking you to follow me in an attempt to +trace the path which has been followed by a scientific idea, in its long +and slow progress from the position of a probable hypothesis to that of +an established law of nature. Our survey has not taken us into very +attractive regions; it has lain, chiefly, in a land flowing with the +abominable, and peopled with mere grubs and mouldiness. And it may be +imagined with what smiles and shrugs, practical and serious +contemporaries of Redi and of Spallanzani may have commented on the waste +of their high abilities in toiling at the solution of problems which, +though curious enough in themselves, could be of no conceivable utility +to mankind. + +Nevertheless, you will have observed that before we had travelled very +far upon our road, there appeared, on the right hand and on the left, +fields laden with a harvest of golden grain, immediately convertible into +those things which the most solidly practical men will admit to have +value--viz., money and life. + +The direct loss to France caused by the Pébrine in seventeen years cannot +be estimated at less than fifty millions sterling; and if we add to this +what Redi's idea, in Pasteur's hands, has done for the wine-grower and +for the vinegar-maker, and try to capitalise its value, we shall find +that it will go a long way towards repairing the money losses caused by +the frightful and calamitous war of this autumn. And as to the equivalent +of Redi's thought in life, how can we over-estimate the value of that +knowledge of the nature of epidemic and epizootic diseases, and +consequently of the means of checking, or eradicating them, the dawn of +which has assuredly commenced? + +Looking back no further than ten years, it is possible to select three +(1863, 1864, and 1869) in which the total number of deaths from scarlet- +fever alone amounted to ninety thousand. That is the return of killed, +the maimed and disabled being left out of sight. Why, it is to be hoped +that the list of killed in the present bloodiest of all wars will not +amount to more than this! But the facts which I have placed before you +must leave the least sanguine without a doubt that the nature and the +causes of this scourge will, one day, be as well understood as those of +the Pébrine are now; and that the long-suffered massacre of our innocents +will come to an end. + +And thus mankind will have one more admonition that "the people perish +for lack of knowledge"; and that the alleviation of the miseries, and the +promotion of the welfare, of men must be sought, by those who will not +lose their pains, in that diligent, patient, loving study of all the +multitudinous aspects of Nature, the results of which constitute exact +knowledge, or Science. It is the justification and the glory of this +great meeting that it is gathered together for no other object than the +advancement of the moiety of science which deals with those phenomena of +nature which we call physical. May its endeavours be crowned with a full +measure of success! + + + +IX + + +GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE + +[1862] + +Merchants occasionally go through a wholesome, though troublesome and not +always satisfactory, process which they term "taking stock." After all +the excitement of speculation, the pleasure of gain, and the pain of +loss, the trader makes up his mind to face facts and to learn the exact +quantity and quality of his solid and reliable possessions. + +The man of science does well sometimes to imitate this procedure; and, +forgetting for the time the importance of his own small winnings, to re- +examine the common stock in trade, so that he may make sure how far the +stock of bullion in the cellar--on the faith of whose existence so much +paper has been circulating--is really the solid gold of truth. + +The Anniversary Meeting of the Geological Society seems to be an occasion +well suited for an undertaking of this kind--for an inquiry, in fact, +into the nature and value of the present results of palaeontological +investigation; and the more so, as all those who have paid close +attention to the late multitudinous discussions in which palaeontology is +implicated, must have felt the urgent necessity of some such scrutiny. + +First in order, as the most definite and unquestionable of all the +results of palaeontology, must be mentioned the immense extension and +impulse given to botany, zoology, and comparative anatomy, by the +investigation of fossil remains. Indeed, the mass of biological facts has +been so greatly increased, and the range of biological speculation has +been so vastly widened, by the researches of the geologist and +palaeontologist, that it is to be feared there are naturalists in +existence who look upon geology as Brindley regarded rivers. "Rivers," +said the great engineer, "were made to feed canals;" and geology, some +seem to think, was solely created to advance comparative anatomy. + +Were such a thought justifiable, it could hardly expect to be received +with favour by this assembly. But it is not justifiable. Your favourite +science has her own great aims independent of all others; and if, +notwithstanding her steady devotion to her own progress, she can scatter +such rich alms among her sisters, it should be remembered that her +charity is of the sort that does not impoverish, but "blesseth him that +gives and him that takes." + +Regard the matter as we will, however, the facts remain. Nearly 40,000 +species of animals and plants have been added to the Systema Naturae by +palaeontological research. This is a living population equivalent to that +of a new continent in mere number; equivalent to that of a new +hemisphere, if we take into account the small population of insects as +yet found fossil, and the large proportion and peculiar organisation of +many of the Vertebrata. + +But, beyond this, it is perhaps not too much to say that, except for the +necessity of interpreting palaeontological facts, the laws of distribution +would have received less careful study; while few comparative anatomists +(and those not of the first order) would have been induced by mere love +of detail, as such, to study the minutiae of osteology, were it not that +in such minutiae lie the only keys to the most interesting riddles offered +by the extinct animal world. + +These assuredly are great and solid gains. Surely it is matter for no +small congratulation that in half a century (for palaeontology, though it +dawned earlier, came into full day only with Cuvier) a subordinate branch +of biology should have doubled the value and the interest of the whole +group of sciences to which it belongs. + +But this is not all. Allied with geology, palaeontology has established +two laws of inestimable importance: the first, that one and the same area +of the earth's surface has been successively occupied by very different +kinds of living beings; the second, that the order of succession +established in one locality holds good, approximately, in all. + +The first of these laws is universal and irreversible; the second is an +induction from a vast number of observations, though it may possibly, and +even probably, have to admit of exceptions. As a consequence of the +second law, it follows that a peculiar relation frequently subsists +between series of strata containing organic remains, in different +localities. The series resemble one another not only in virtue of a +general resemblance of the organic remains in the two, but also in virtue +of a resemblance in the order and character of the serial succession in +each. There is a resemblance of arrangement; so that the separate terms +of each series, as well as the whole series, exhibit a correspondence. + +Succession implies time; the lower members of an undisturbed series of +sedimentary rocks are certainly older than the upper; and when the notion +of age was once introduced as the equivalent of succession, it was no +wonder that correspondence in succession came to be looked upon as a +correspondence in age, or "contemporaneity." And, indeed, so long as +relative age only is spoken of, correspondence in succession _is_ +correspondence in age; it is _relative_ contemporaneity. + +But it would have been very much better for geology if so loose and +ambiguous a word as "contemporaneous" had been excluded from her +terminology, and if, in its stead, some term expressing similarity of +serial relation, and excluding the notion of time altogether, had been +employed to denote correspondence in position in two or more series of +strata. + +In anatomy, where such correspondence of position has constantly to be +spoken of, it is denoted by the word "homology" and its derivatives; and +for Geology (which after all is only the anatomy and physiology of the +earth) it might be well to invent some single word, such as "homotaxis" +(similarity of order), in order to express an essentially similar idea. +This, however, has not been done, and most probably the inquiry will at +once be made--To what end burden science with a new and strange term in +place of one old, familiar, and part of our common language? + +The reply to this question will become obvious as the inquiry into the +results of palaeontology is pushed further. + +Those whose business it is to acquaint themselves specially with the +works of palaeontologists, in fact, will be fully aware that very few, if +any, would rest satisfied with such a statement of the conclusions of +their branch of biology as that which has just been given. + +Our standard repertories of palaeontology profess to teach us far higher +things--to disclose the entire succession of living forms upon the +surface of the globe; to tell us of a wholly different distribution of +climatic conditions in ancient times; to reveal the character of the +first of all living existences; and to trace out the law of progress from +them to us. + +It may not be unprofitable to bestow on these professions a somewhat more +critical examination than they have hitherto received, in order to +ascertain how far they rest on an irrefragable basis; or whether, after +all, it might not be well for palaeontologists to learn a little more +carefully that scientific "ars artium," the art of saying "I don't know." +And to this end let us define somewhat more exactly the extent of these +pretensions of palaeontology. + +Every one is aware that Professor Bronn's "Untersuchungen" and Professor +Pictet's "Traité de Paléontologie" are works of standard authority, +familiarly consulted by every working palaeontologist. It is desirable to +speak of these excellent books, and of their distinguished authors, with +the utmost respect, and in a tone as far as possible removed from carping +criticism; indeed, if they are specially cited in this place, it is +merely in justification of the assertion that the following propositions, +which may be found implicitly, or explicitly, in the works in question, +are regarded by the mass of palaeontologists and geologists, not only on +the Continent but in this country, as expressing some of the best- +established results of palaeontology. Thus:-- + +Animals and plants began their existence together, not long after the +commencement of the deposition of the sedimentary rocks; and then +succeeded one another, in such a manner, that totally distinct faunae and +florae occupied the whole surface of the earth, one after the other, and +during distinct epochs of time. + +A geological formation is the sum of all the strata deposited over the +whole surface of the earth during one of these epochs: a geological fauna +or flora is the sum of all the species of animals or plants which +occupied the whole surface of the globe, during one of these epochs. + +The population of the earth's surface was at first very similar in all +parts, and only from the middle of the Tertiary epoch onwards, began to +show a distinct distribution in zones. + +The constitution of the original population, as well as the numerical +proportions of its members, indicates a warmer and, on the whole, +somewhat tropical climate, which remained tolerably equable throughout +the year. The subsequent distribution of living beings in zones is the +result of a gradual lowering of the general temperature, which first +began to be felt at the poles. + +It is not now proposed to inquire whether these doctrines are true or +false; but to direct your attention to a much simpler though very +essential preliminary question--What is their logical basis? what are the +fundamental assumptions upon which they all logically depend? and what is +the evidence on which those fundamental propositions demand our assent? + +These assumptions are two: the first, that the commencement of the +geological record is coëval with the commencement of life on the globe; +the second, that geological contemporaneity is the same thing as +chronological synchrony. Without the first of these assumptions there +would of course be no ground for any statement respecting the +commencement of life; without the second, all the other statements cited, +every one of which implies a knowledge of the state of different parts of +the earth at one and the same time, will be no less devoid of +demonstration. + +The first assumption obviously rests entirely on negative evidence. This +is, of course, the only evidence that ever can be available to prove the +commencement of any series of phenomena; but, at the same time, it must +be recollected that the value of negative evidence depends entirely on +the amount of positive corroboration it receives. If A.B. wishes to prove +an _alibi_, it is of no use for him to get a thousand witnesses simply to +swear that they did not see him in such and such a place, unless the +witnesses are prepared to prove that they must have seen him had he been +there. But the evidence that animal life commenced with the Lingula- +flags, _e.g._, would seem to be exactly of this unsatisfactory +uncorroborated sort. The Cambrian witnesses simply swear they "haven't +seen anybody their way"; upon which the counsel for the other side +immediately puts in ten or twelve thousand feet of Devonian sandstones to +make oath they never saw a fish or a mollusk, though all the world knows +there were plenty in their time. + +But then it is urged that, though the Devonian rocks in one part of the +world exhibit no fossils, in another they do, while the lower Cambrian +rocks nowhere exhibit fossils, and hence no living being could have +existed in their epoch. + +To this there are two replies: the first that the observational basis of +the assertion that the lowest rocks are nowhere fossiliferous is an +amazingly small one, seeing how very small an area, in comparison to that +of the whole world, has yet been fully searched; the second, that the +argument is good for nothing unless the unfossiliferous rocks in question +were not only _contemporaneous_ in the geological sense, but +_synchronous_ in the chronological sense. To use the _alibi_ illustration +again. If a man wishes to prove he was in neither of two places, A and B, +on a given day, his witnesses for each place must be prepared to answer +for the whole day. If they can only prove that he was not at A in the +morning, and not at B in the afternoon, the evidence of his absence from +both is nil, because he might have been at B in the morning and at A in +the afternoon. + +Thus everything depends upon the validity of the second assumption. And +we must proceed to inquire what is the real meaning of the word +"contemporaneous" as employed by geologists. To this end a concrete +example may be taken. + +The Lias of England and the Lias of Germany, the Cretaceous rocks of +Britain and the Cretaceous rocks of Southern India, are termed by +geologists "contemporaneous" formations; but whenever any thoughtful +geologist is asked whether he means to say that they were deposited +synchronously, he says, "No,--only within the same great epoch." And if, +in pursuing the inquiry, he is asked what may be the approximate value in +time of a "great epoch"--whether it means a hundred years, or a thousand, +or a million, or ten million years--his reply is, "I cannot tell." + +If the further question be put, whether physical geology is in possession +of any method by which the actual synchrony (or the reverse) of any two +distant deposits can be ascertained, no such method can be heard of; it +being admitted by all the best authorities that neither similarity of +mineral composition, nor of physical character, nor even direct +continuity of stratum, are _absolute_ proofs of the synchronism of even +approximated sedimentary strata: while, for distant deposits, there seems +to be no kind of physical evidence attainable of a nature competent to +decide whether such deposits were formed simultaneously, or whether they +possess any given difference of antiquity. To return to an example +already given: All competent authorities will probably assent to the +proposition that physical geology does not enable us in any way to reply +to this question--Were the British Cretaceous rocks deposited at the same +time as those of India, or are they a million of years younger or a +million of years older? + +Is palaeontology able to succeed where physical geology fails? Standard +writers on palaeontology, as has been seen, assume that she can. They take +it for granted, that deposits containing similar organic remains are +synchronous--at any rate in a broad sense; and yet, those who will study +the eleventh and twelfth chapters of Sir Henry De La Beche's remarkable +"Researches in Theoretical Geology," published now nearly thirty years +ago, and will carry out the arguments there most luminously stated, to +their logical consequences, may very easily convince themselves that even +absolute identity of organic contents is no proof of the synchrony of +deposits, while absolute diversity is no proof of difference of date. Sir +Henry De La Beche goes even further, and adduces conclusive evidence to +show that the different parts of one and the same stratum, having a +similar composition throughout, containing the same organic remains, and +having similar beds above and below it, may yet differ to any conceivable +extent in age. + +Edward Forbes was in the habit of asserting that the similarity of the +organic contents of distant formations was _prima facie_ evidence, not of +their similarity, but of their difference of age; and holding as he did +the doctrine of single specific centres, the conclusion was as legitimate +as any other; for the two districts must have been occupied by migration +from one of the two, or from an intermediate spot, and the chances +against exact coincidence of migration and of imbedding are infinite. + +In point of fact, however, whether the hypothesis of single or of +multiple specific centres be adopted, similarity of organic contents +cannot possibly afford any proof of the synchrony of the deposits which +contain them; on the contrary, it is demonstrably compatible with the +lapse of the most prodigious intervals of time, and with the +interposition of vast changes in the organic and inorganic worlds, +between the epochs in which such deposits were formed. + +On what amount of similarity of their faunae is the doctrine of the +contemporaneity of the European and of the North American Silurians +based? In the last edition of Sir Charles Lyell's "Elementary Geology" it +is stated, on the authority of a former President of this Society, the +late Daniel Sharpe, that between 30 and 40 per cent. of the species of +Silurian Mollusca are common to both sides of the Atlantic. By way of due +allowance for further discovery, let us double the lesser number and +suppose that 60 per cent. of the species are common to the North American +and the British Silurians. Sixty per cent. of species in common is, then, +proof of contemporaneity. + +Now suppose that, a million or two of years hence, when Britain has made +another dip beneath the sea and has come up again, some geologist applies +this doctrine, in comparing the strata laid bare by the upheaval of the +bottom, say, of St. George's Channel with what may then remain of the +Suffolk Crag. Reasoning in the same way, he will at once decide the +Suffolk Crag and the St. George's Channel beds to be contemporaneous; +although we happen to know that a vast period (even in the geological +sense) of time, and physical changes of almost unprecedented extent, +separate the two. But if it be a demonstrable fact that strata +containing more than 60 or 70 per cent. of species of Mollusca in common, +and comparatively close together, may yet be separated by an amount of +geological time sufficient to allow of some of the greatest physical +changes the world has seen, what becomes of that sort of contemporaneity +the sole evidence of which is a similarity of facies, or the identity of +half a dozen species, or of a good many genera? + +And yet there is no better evidence for the contemporaneity assumed by +all who adopt the hypothesis of universal faunae and florae, of a +universally uniform climate, and of a sensible cooling of the globe +during geological time. + +There seems, then, no escape from the admission that neither physical +geology, nor palaeontology, possesses any method by which the absolute +synchronism of two strata can be demonstrated. All that geology can prove +is local order of succession. It is mathematically certain that, in any +given vertical linear section of an undisturbed series of sedimentary +deposits, the bed which lies lowest is the oldest. In many other vertical +linear sections of the same series, of course, corresponding beds will +occur in a similar order; but, however great may be the probability, no +man can say with absolute certainty that the beds in the two sections +were synchronously deposited. For areas of moderate extent, it is +doubtless true that no practical evil is likely to result from assuming +the corresponding beds to be synchronous or strictly contemporaneous; and +there are multitudes of accessory circumstances which may fully justify +the assumption of such synchrony. But the moment the geologist has to +deal with large areas, or with completely separated deposits, the +mischief of confounding that "homotaxis" or "similarity of arrangement," +which _can_ be demonstrated, with "synchrony" or "identity of date," for +which there is not a shadow of proof, under the one common term of +"contemporaneity" becomes incalculable, and proves the constant source of +gratuitous speculations. + +For anything that geology or palaeontology are able to show to the +contrary, a Devonian fauna and flora in the British Islands may have been +contemporaneous with Silurian life in North America, and with a +Carboniferous fauna and flora in Africa. Geographical provinces and zones +may have been as distinctly marked in the Palaeozoic epoch as at present, +and those seemingly sudden appearances of new genera and species, which +we ascribe to new creation, may be simple results of migration. + +It may be so; it may be otherwise. In the present condition of our +knowledge and of our methods, one verdict--"not proven, and not +provable"--must be recorded against all the grand hypotheses of the +palaeontologist respecting the general succession of life on the globe. +The order and nature of terrestrial life, as a whole, are open questions. +Geology at present provides us with most valuable topographical records, +but she has not the means of working them into a universal history. Is +such a universal history, then, to be regarded as unattainable? Are all +the grandest and most interesting problems which offer themselves to the +geological student, essentially insoluble? Is he in the position of a +scientific Tantalus--doomed always to thirst for a knowledge which he +cannot obtain? The reverse is to be hoped; nay, it may not be impossible +to indicate the source whence help will come. + +In commencing these remarks, mention was made of the great obligations +under which the naturalist lies to the geologist and palaeontologist. +Assuredly the time will come when these obligations will be repaid +tenfold, and when the maze of the world's past history, through which the +pure geologist and the pure palaeontologist find no guidance, will be +securely threaded by the clue furnished by the naturalist. + +All who are competent to express an opinion on the subject are, at +present, agreed that the manifold varieties of animal and vegetable form +have not either come into existence by chance, nor result from capricious +exertions of creative power; but that they have taken place in a definite +order, the statement of which order is what men of science term a natural +law. Whether such a law is to be regarded as an expression of the mode of +operation of natural forces, or whether it is simply a statement of the +manner in which a supernatural power has thought fit to act, is a +secondary question, so long as the existence of the law and the +possibility of its discovery by the human intellect are granted. But he +must be a half-hearted philosopher who, believing in that possibility, +and having watched the gigantic strides of the biological sciences during +the last twenty years, doubts that science will sooner or later make this +further step, so as to become possessed of the law of evolution of +organic forms--of the unvarying order of that great chain of causes and +effects of which all organic forms, ancient and modern, are the links. +And then, if ever, we shall be able to begin to discuss, with profit, the +questions respecting the commencement of life, and the nature of the +successive populations of the globe, which so many seem to think are +already answered. + +The preceding arguments make no particular claim to novelty; indeed they +have been floating more or less distinctly before the minds of geologists +for the last thirty years; and if, at the present time, it has seemed +desirable to give them more definite and systematic expression, it is +because palaeontology is every day assuming a greater importance, and now +requires to rest on a basis the firmness of which is thoroughly well +assured. Among its fundamental conceptions, there must be no confusion +between what is certain and what is more or less probable.[1] But, +pending the construction of a surer foundation than palaeontology now +possesses, it may be instructive, assuming for the nonce the general +correctness of the ordinary hypothesis of geological contemporaneity, to +consider whether the deductions which are ordinarily drawn from the whole +body of palaeontological facts are justifiable. + +[Footnote 1: "Le plus grand service qu'on puisse rendre à la science est +d'y faire place nette avant d'y rien construire."--CUVIER.] + +The evidence on which such conclusions are based is of two kinds, +negative and positive. The value of negative evidence, in connection with +this inquiry, has been so fully and clearly discussed in an address from +the chair of this Society,[2] which none of us have forgotten, that +nothing need at present be said about it; the more, as the considerations +which have been laid before you have certainly not tended to increase +your estimation of such evidence. It will be preferable to turn to the +positive facts of palaeontology, and to inquire what they tell us. + +[Footnote 2: Anniversary Address for 1851, _Quart. Journ. Geol. Soc._ +vol. vii.] + +We are all accustomed to speak of the number and the extent of the +changes in the living population of the globe during geological time as +something enormous: and indeed they are so, if we regard only the +negative differences which separate the older rocks from the more modern, +and if we look upon specific and generic changes as great changes, which +from one point of view, they truly are. But leaving the negative +differences out of consideration, and looking only at the positive data +furnished by the fossil world from a broader point of view--from that of +the comparative anatomist who has made the study of the greater +modifications of animal form his chief business--a surprise of another +kind dawns upon the mind; and under _this_ aspect the smallness of the +total change becomes as astonishing as was its greatness under the other. + +There are two hundred known orders of plants; of these not one is +certainly known to exist exclusively in the fossil state. The whole lapse +of geological time has as yet yielded not a single new ordinal type of +vegetable structure.[3] + +[Footnote 3: See Hooker's _Introductory Essay to the Flora of Tasmania_, +p. xxiii.] + +The positive change in passing from the recent to the ancient animal +world is greater, but still singularly small. No fossil animal is so +distinct from those now living as to require to be arranged even in a +separate class from those which contain existing forms. It is only when +we come to the orders, which may be roughly estimated at about a hundred +and thirty, that we meet with fossil animals so distinct from those now +living as to require orders for themselves; and these do not amount, on +the most liberal estimate, to more than about 10 per cent. of the whole. + +There is no certainly known extinct order of Protozoa; there is but one +among the Coelenterata--that of the rugose corals; there is none among +the Mollusca; there are three, the Cystidea, Blastoidea, and +Edrioasterida, among the Echinoderms; and two, the Trilobita and +Eurypterida, among the Crustacea; making altogether five for the great +sub-kingdom of Annulosa. Among Vertebrates there is no ordinally distinct +fossil fish: there is only one extinct order of Amphibia--the +Labyrinthodonts; but there are at least four distinct orders of Reptilia, +viz. the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, and +perhaps another or two. There is no known extinct order of Birds, and no +certainly known extinct order of Mammals, the ordinal distinctness of the +"Toxodontia" being doubtful. + +The objection that broad statements of this kind, after all, rest largely +on negative evidence is obvious, but it has less force than may at first +be supposed; for, as might be expected from the circumstances of the +case, we possess more abundant positive evidence regarding Fishes and +marine Mollusks than respecting any other forms of animal life; and yet +these offer us, through the whole range of geological time, no species +ordinally distinct from those now living; while the far less numerous +class of Echinoderms presents three, and the Crustacea two, such orders, +though none of these come down later than the Palaeozoic age. Lastly, the +Reptilia present the extraordinary and exceptional phenomenon of as many +extinct as existing orders, if not more; the four mentioned maintaining +their existence from the Lias to the Chalk inclusive. + +Some years ago one of your Secretaries pointed out another kind of +positive palaeontological evidence tending towards the same conclusion-- +afforded by the existence of what he termed "persistent types" of +vegetable and of animal life.[4] He stated, on the authority of Dr. +Hooker, that there are Carboniferous plants which appear to be +generically identical with some now living; that the cone of the Oolitic +_Araucaria_ is hardly distinguishable from that of an existing species; +that a true _Pinus_ appears in the Purbecks and a _Juglans_ in the Chalk; +while, from the Bagshot Sands, a _Banksia_, the wood of which is not +distinguishable from that of species now living in Australia, had been +obtained. + +[Footnote 4: See the abstract of a Lecture "On the Persistent Types of +Animal Life," in the _Notices of the Meetings of the Royal Institution of +Great Britain_.--June 3, 1859, vol. iii. p. 151.] + +Turning to the animal kingdom, he affirmed the tabulate corals of the +Silurian rocks to be wonderfully like those which now exist; while even +the families of the Aporosa were all represented in the older Mesozoic +rocks. + +Among the Mollusca similar facts were adduced. Let it be borne in mind +that _Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina, +Orbicula, Lingula, Rhynchonclla_, and _Nautilus_, all of which are +existing _genera_, are given without a doubt as Silurian in the last +edition of "Siluria"; while the highest forms of the highest Cephalopods +are represented in the Lias by a genus _Belemnoteuthis_, which presents +the closest relation to the existing _Loligo_. + +The two highest groups of the Annulosa, the Insecta and the Arachnida, +are represented in the Coal, either by existing genera, or by forms +differing from existing genera in quite minor peculiarities. + +Turning to the Vertebrata, the only palaeozoic Elasmobranch Fish of which +we have any complete knowledge is the Devonian and Carboniferous +_Pleuracanthus_, which differs no more from existing Sharks than these do +from one another. + +Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and +great as is their range in time, a large mass of evidence has recently +been adduced to show that almost all those respecting which we possess +sufficient information, are referable to the same sub-ordinal groups as +the existing _Lepidosteus, Polypterus_, and Sturgeon; and that a singular +relation obtains between the older and the younger Fishes; the former, +the Devonian Ganoids, being almost all members of the same sub-order as +_Polypterus_, while the Mesozoic Ganoids are almost all similarly allied +to _Lepidosteus_.[5] + +[Footnote 5: "Memoirs of the Geological Survey of the United Kingdom.-- +Decade x. Preliminary Essay upon the Systematic Arrangement of the Fishes +of the Devonian Epoch."] + +Again, what can be more remarkable than the singular constancy of +structure preserved throughout a vast period of time by the family of the +Pycnodonts and by that of the true Coelacanths; the former persisting, +with but insignificant modifications, from the Carboniferous to the +Tertiary rocks, inclusive; the latter existing, with still less change, +from the Carboniferous rocks to the Chalk, inclusive? + +Among Reptiles, the highest living group, that of the Crocodilia, is +represented, at the early part of the Mesozoic epoch, by species +identical in the essential characters of their organisation with those +now living, and differing from the latter only in such matters as the +form of the articular facets of the vertebral centra, in the extent to +which the nasal passages are separated from the cavity of the mouth by +bone, and in the proportions of the limbs. + +And even as regards the Mammalia, the scanty remains of Triassic and +Oolitic species afford no foundation for the supposition that the +organisation of the oldest forms differed nearly so much from some of +those which now live as these differ from one another. + +It is needless to multiply these instances; enough has been said to +justify the statement that, in view of the immense diversity of known +animal and vegetable forms, and the enormous lapse of time indicated by +the accumulation of fossiliferous strata, the only circumstance to be +wondered at is, not that the changes of life, as exhibited by positive +evidence, have been so great but that they have been so small. + +Be they great or small, however, it is desirable to attempt to estimate +them. Let us, therefore, take each great division of the animal world in +succession, and, whenever an order or a family can be shown to have had a +prolonged existence, let us endeavour to ascertain how far the later +members of the group differ from the earlier ones. If these later +members, in all or in many cases, exhibit a certain amount of +modification, the fact is, so far, evidence in favour of a general law of +change; and, in a rough way, the rapidity of that change will be measured +by the demonstrable amount of modification. On the other hand, it must be +recollected that the absence of any modification, while it may leave the +doctrine of the existence of a law of change without positive support, +cannot possibly disprove all forms of that doctrine, though it may afford +a sufficient refutation of many of them. + +The PROTOZOA.--The Protozoa are represented throughout the whole range of +geological series, from the Lower Silurian formation to the present day. +The most ancient forms recently made known by Ehrenberg are exceedingly +like those which now exist: no one has ever pretended that the difference +between any ancient and any modern Foraminifera is of more than generic +value, nor are the oldest Foraminifera either simpler, more embryonic, or +less differentiated, than the existing forms. + +The COELENTERATA.--The Tabulate Corals have existed from the Silurian +epoch to the present day, but I am not aware that the ancient +_Heliolites_ possesses a single mark of a more embryonic or less +differentiated character, or less high organisation, than the existing +_Heliopora_. As for the Aporose Corals, in what respect is the Silurian +_Paloeocyclus_ less highly organised or more embryonic than the modern +_Fungia_, or the Liassic Aporosa than the existing members of the same +families? + +The _Mollusca_--In what sense is the living _Waldheimia_ less embryonic, +or more specialised, than the palaeozoic _Spirifer_; or the existing +_Rhynchonelloe, Cranioe, Discinoe, Linguloe_, than the Silurian species +of the same genera? In what sense can _Loligo_ or _Spirula_ be said to be +more specialised, or less embryonic, than _Belemnites_; or the modern +species of Lamellibranch and Gasteropod genera, than the Silurian species +of the same genera? + +The ANNULOSA.--The Carboniferous Insecta and Arachnida are neither less +specialised, nor more embryonic, than these that now live, nor are the +Liassic Cirripedia and Macrura; while several of the Brachyura, which +appear in the Chalk, belong to existing genera; and none exhibit either +an intermediate, or an embryonic, character. + +The VERTEBRATA.--Among fishes I have referred to the Coelacanthini +(comprising the genera _Coelacanthus, Holophagus, Undina_, and +_Macropoma_) as affording an example of a persistent type; and it is most +remarkable to note the smallness of the differences between any of these +fishes (affecting at most the proportions of the body and fins, and the +character and sculpture of the scales), notwithstanding their enormous +range in time. In all the essentials of its very peculiar structure, the +_Macropoma_ of the Chalk is identical with the _Coelacanthus_ of the +Coal. Look at the genus _Lepidotus_, again, persisting without a +modification of importance from the Liassic to the Eocene formations +inclusively. + +Or among the Teleostei--in what respect is the _Beryx_ of the Chalk more +embryonic, or less differentiated, than _Beryx lineatus_ of King George's +Sound? + +Or to turn to the higher Vertebrata--in what sense are the Liassic +Chelonia inferior to those which now exist? How are the Cretaceous +Ichthyosauria, Plesiosauria, or Pterosauria less embryonic, or more +differentiated, species than those of the Lias? + +Or lastly, in what circumstance is the _Phascolotherium_ more embryonic, +or of a more generalised type, than the modern Opossum; or a _Lophiodon_, +or a _Paloeotherium_, than a modern _Tapirus_ or _Hyrax_? + +These examples might be almost indefinitely multiplied, but surely they +are sufficient to prove that the only safe and unquestionable testimony +we can procure--positive evidence--fails to demonstrate any sort of +progressive modification towards a less embryonic, or less generalised, +type in a great many groups of animals of long-continued geological +existence. In these groups there is abundant evidence of variation--none +of what is ordinarily understood as progression; and, if the known +geological record is to be regarded as even any considerable fragment of +the whole, it is inconceivable that any theory of a necessarily +progressive development can stand, for the numerous orders and families +cited afford no trace of such a process. + +But it is a most remarkable fact, that, while the groups which have been +mentioned, and many besides, exhibit no sign of progressive modification, +there are others, co-existing with them, under the same conditions, in +which more or less distinct indications of such a process seems to be +traceable. Among such indications I may remind you of the predominance of +Holostome Gasteropoda in the older rocks as compared with that of +Siphonostone Gasteropoda in the later. A case less open to the objection +of negative evidence, however, is that afforded by the Tetrabranchiate +Cephalopoda, the forms of the shells and of the septal sutures exhibiting +a certain increase of complexity in the newer genera. Here, however, one +is met at once with the occurrence of _Orthoceras_ and _Baculites_ at the +two ends of the series, and of the fact that one of the simplest genera, +_Nautilus_, is that which now exists. + +The Crinoidea, in the abundance of stalked forms in the ancient +formations as compared with their present rarity, seem to present us with +a fair case of modification from a more embryonic towards a less +embryonic condition. But then, on careful consideration of the facts, the +objection arises that the stalk, calyx, and arms of the palaeozoic Crinoid +are exceedingly different from the corresponding organs of a larval +_Comatula_; and it might with perfect justice be argued that +_Actinocrinus_ and _Eucalyptocrinus_, for example, depart to the full as +widely, in one direction, from the stalked embryo of _Comatula_, as +_Comatula_ itself does in the other. + +The Echinidea, again, are frequently quoted as exhibiting a gradual +passage from a more generalised to a more specialised type, seeing that +the elongated, or oval, Spatangoids appear after the spheroidal +Echinoids. But here it might be argued, on the other hand, that the +spheroidal Echinoids, in reality, depart further from the general plan +and from the embryonic form than the elongated Spatangoids do; and that +the peculiar dental apparatus and the pedicellariae of the former are +marks of at least as great differentiation as the petaloid ambulacra and +semitae of the latter. + +Once more, the prevalence of Macrurous before Brachyurous Podophthalmia +is, apparently, a fair piece of evidence in favour of progressive +modification in the same order of Crustacea; and yet the case will not +stand much sifting, seeing that the Macrurous Podophthalmia depart as far +in one direction from the common type of Podophthalmia, or from any +embryonic condition of the Brachyura, as the Brachyura do in the other; +and that the middle terms between Macrura and Brachyura--the Anomura--are +little better represented in the older Mesozoic rocks than the Brachyura +are. + +None of the cases of progressive modification which are cited from among +the Invertebrata appear to me to have a foundation less open to criticism +than these; and if this be so, no careful reasoner would, I think, be +inclined to lay very great stress upon them. Among the Vertebrata, +however, there are a few examples which appear to be far less open to +objection. + +It is, in fact, true of several groups of Vertebrata which have lived +through a considerable range of time, that the endoskeleton (more +particularly the spinal column) of the older genera presents a less +ossified, and, so far, less differentiated, condition than that of the +younger genera. Thus the Devonian Ganoids, though almost all members of +the same sub-order as _Polypterus_, and presenting numerous important +resemblances to the existing genus, which possesses biconclave vertebrae, +are, for the most part, wholly devoid of ossified vertebral centra. The +Mesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, while +the existing _Lepidosteus_ has Salamandroid, opisthocoelous, vertebrae. +So, none of the Palaeozoic Sharks have shown themselves to be possessed of +ossified vertebrae, while the majority of modern Sharks possess such +vertebrae. Again, the more ancient Crocodilia and Lacertilia have vertebrae +with the articular facets of their centra flattened or biconcave, while +the modern members of the same group have them procoelous. But the most +remarkable examples of progressive modification of the vertebral column, +in correspondence with geological age, are those afforded by the +Pycnodonts among fish, and the Labyrinthodonts among Amphibia. + +The late able ichthyologist Heckel pointed out the fact, that, while the +Pycnodonts never possess true vertebral centra, they differ in the degree +of expansion and extension of the ends of the bony arches of the vertebrae +upon the sheath of the notochord; the Carboniferous forms exhibiting +hardly any such expansion, while the Mesozoic genera present a greater +and greater development, until, in the Tertiary forms, the expanded ends +become suturally united so as to form a sort of false vertebra. Hermann +von Meyer, again, to whose luminous researches we are indebted for our +present large knowledge of the organisation of the older Labyrinthodonts, +has proved that the Carboniferous _Archegosaurus_ had very imperfectly +developed vertebral centra, while the Triassic _Mastodonsaurus_ had the +same parts completely ossified.[6] + +[Footnote 6: As this Address is passing through the press (March 7, +1862), evidence lies before me of the existence of a new Labyrinthodont +(_Pholidogaster_), from the Edinburgh coal-field with well-ossified +vertebral centra.] + +The regularity and evenness of the dentition of the _Anoplotherium_, as +contrasted with that of existing Artiodactyles, and the assumed nearer +approach of the dentition of certain ancient Carnivores to the typical +arrangement, have also been cited as exemplifications of a law of +progressive development, but I know of no other cases based on positive +evidence which are worthy of particular notice. + +What then does an impartial survey of the positively ascertained truths +of palaeontology testify in relation to the common doctrines of +progressive modification, which suppose that modification to have taken +place by a necessary progress from more to less embryonic forms, or from +more to less generalised types, within the limits of the period +represented by the fossiliferous rocks? + +It negatives those doctrines; for it either shows us no evidence of any +such modification, or demonstrates it to have been very slight; and as to +the nature of that modification, it yields no evidence whatsoever that +the earlier members of any long-continued group were more generalised in +structure than the later ones. To a certain extent, indeed, it may be +said that imperfect ossification of the vertebral column is an embryonic +character; but, on the other hand, it would be extremely incorrect to +suppose that the vertebral columns of the older Vertebrata are in any +sense embryonic in their whole structure. + +Obviously, if the earliest fossiliferous rocks now known are coëval with +the commencement of life, and if their contents give us any just +conception of the nature and the extent of the earliest fauna and flora, +the insignificant amount of modification which can be demonstrated to +have taken place in any one group of animals, or plants, is quite +incompatible with the hypothesis that all living forms are the results of +a necessary process of progressive development, entirely comprised within +the time represented by the fossiliferous rocks. + +Contrariwise, any admissible hypothesis of progressive modification must +be compatible with persistence without progression, through indefinite +periods. And should such an hypothesis eventually be proved to be true, +in the only way in which it can be demonstrated, viz. by observation and +experiment upon the existing forms of life, the conclusion will +inevitably present itself, that the Palaeozoic Mesozoic, and Cainozoic +faunae and florae, taken together, bear somewhat the same proportion to the +whole series of living beings which have occupied this globe, as the +existing fauna and flora do to them. + +Such are the results of palaeontology as they appear, and have for some +years appeared, to the mind of an inquirer who regards that study simply +as one of the applications of the great biological sciences, and who +desires to see it placed upon the same sound basis as other branches of +physical inquiry. If the arguments which have been brought forward are +valid, probably no one, in view of the present state of opinion, will be +inclined to think the time wasted which has been spent upon their +elaboration. + + + +X + + +GEOLOGICAL REFORM + +[1869] + +"A great reform in geological speculation seems now to have become +necessary." + +"It is quite certain that a great mistake has been made--that British +popular geology at the present time is in direct opposition to the +principles of Natural Philosophy."[1] + +[Footnote 1: On Geological Time. By Sir W. Thomson, LL.D. _Transactions +of the Geological Society of Glasgow_, vol. iii.] + +In reviewing the course of geological thought during the past year, for +the purpose of discovering those matters to which I might most fitly +direct your attention in the Address which it now becomes my duty to +deliver from the Presidential Chair, the two somewhat alarming sentences +which I have just read, and which occur in an able and interesting essay +by an eminent natural philosopher, rose into such prominence before my +mind that they eclipsed everything else. + +It surely is a matter of paramount importance for the British geologists +(some of them very popular geologists too) here in solemn annual session +assembled, to inquire whether the severe judgment thus passed upon them +by so high an authority as Sir William Thomson is one to which they must +plead guilty _sans phrase_, or whether they are prepared to say "not +guilty," and appeal for a reversal of the sentence to that higher court +of educated scientific opinion to which we are all amenable. + +As your attorney-general for the time being, I thought I could not do +better than get up the case with a view of advising you. It is true that +the charges brought forward by the other side involve the consideration +of matters quite foreign to the pursuits with which I am ordinarily +occupied; but, in that respect, I am only in the position which is, nine +times out of ten, occupied by counsel, who nevertheless contrive to gain +their causes, mainly by force of mother-wit and common-sense, aided by +some training in other intellectual exercises. + +Nerved by such precedents, I proceed to put my pleading before you. + +And the first question with which I propose to deal is, What is it to +which Sir W. Thomson refers when he speaks of "geological speculation" +and "British popular geology"? + +I find three, more or less contradictory, systems of geological thought, +each of which might fairly enough claim these appellations, standing side +by side in Britain. I shall call one of them CATASTROPHISM, another +UNIFORMITARIANISM, the third EVOLUTIONISM; and I shall try briefly to +sketch the characters of each, that you may say whether the +classification is, or is not, exhaustive. + +By CATASTROPHISM, I mean any form of geological speculation which, in +order to account for the phenomena of geology, supposes the operation of +forces different in their nature, or immeasurably different in power, +from those which we at present see in action in the universe. + +The Mosaic cosmogony is, in this sense, catastrophic, because it assumes +the operation of extra-natural power. The doctrine of violent upheavals, +_débâcles_, and cataclysms in general, is catastrophic, so far as it +assumes that these were brought about by causes which have now no +parallel. There was a time when catastrophism might, pre-eminently, have +claimed the title of "British popular geology"; and assuredly it has yet +many adherents, and reckons among its supporters some of the most +honoured members of this Society. + +By UNIFORMITARIANISM, I mean especially, the teaching of Hutton and of +Lyell. + +That great though incomplete work, "The Theory of the Earth," seems to me +to be one of the most remarkable contributions to geology which is +recorded in the annals of the science. So far as the not-living world is +concerned, uniformitarianism lies there, not only in germ, but in blossom +and fruit. + +If one asks how it is that Hutton was led to entertain views so far in +advance of those prevalent in his time, in some respects; while, in +others, they seem almost curiously limited, the answer appears to me to +be plain. + +Hutton was in advance of the geological speculation of his time, because, +in the first place, he had amassed a vast store of knowledge of the facts +of geology, gathered by personal observation in travels of considerable +extent; and because, in the second place, he was thoroughly trained in +the physical and chemical science of his day, and thus possessed, as much +as any one in his time could possess it, the knowledge which is requisite +for the just interpretation of geological phenomena, and the habit of +thought which fits a man for scientific inquiry. + +It is to this thorough scientific training that I ascribe Hutton's steady +and persistent refusal to look to other causes than those now in +operation, for the explanation of geological phenomena. + +Thus he writes:--"I do not pretend, as he [M. de Luc] does in his theory, +to describe the beginning of things. I take things such as I find them at +present; and from these I reason with regard to that which must have +been."[2] + +[Footnote 2: _The Theory of the Earth_, vol. i. p. 173, note.] + +And again:--"A theory of the earth, which has for object truth, can have +no retrospect to that which had preceded the present order of the world; +for this order alone is what we have to reason upon; and to reason +without data is nothing but delusion. A theory, therefore, which is +limited to the actual constitution of this earth cannot be allowed to +proceed one step beyond the present order of things."[3] + +[Footnote 3: _Ibid._, vol. i. p. 281.] + +And so clear is he, that no causes beside such as are now in operation +are needed to account for the character and disposition of the components +of the crust of the earth, that he says, broadly and boldly:--" ... There +is no part of the earth which has not had the same origin, so far as this +consists in that earth being collected at the bottom of the sea, and +afterwards produced, as land, along with masses of melted substances, by +the operation of mineral causes."[4] + +[Footnote 4: _Ibid._. p. 371.] + +But other influences were at work upon Hutton beside those of a mind +logical by nature, and scientific by sound training; and the peculiar +turn which his speculations took seems to me to be unintelligible, unless +these be taken into account. The arguments of the French astronomers and +mathematicians, which, at the end of the last century, were held to +demonstrate the existence of a compensating arrangement among the +celestial bodies, whereby all perturbations eventually reduced themselves +to oscillations on each side of a mean position, and the stability of the +solar system was secured, had evidently taken strong hold of Hutton's +mind. + +In those oddly constructed periods which seem to have prejudiced many +persons against reading his works, but which are full of that peculiar, +if unattractive, eloquence which flows from mastery of the subject, +Hutton says:-- + +"We have now got to the end of our reasoning; we have no data further to +conclude immediately from that which actually is. But we have got enough; +we have the satisfaction to find, that in Nature there is wisdom, system, +and consistency. For having, in the natural history of this earth, seen a +succession of worlds, we may from this conclude that there is a system in +Nature; in like manner as, from seeing revolutions of the planets, it is +concluded, that there is a system by which they are intended to continue +those revolutions. But if the succession of worlds is established in the +system of nature, it is in vain to look for anything higher in the origin +of the earth. The result, therefore, of this physical inquiry is, that we +find no vestige of a beginning,--no prospect of an end."[5] + +[Footnote 5: _Ibid._, vol. i. p. 200.] + +Yet another influence worked strongly upon Hutton. Like most philosophers +of his age, he coquetted with those final causes which have been named +barren virgins, but which might be more fitly termed the _hetairoe_ of +philosophy, so constantly have they led men astray. The final cause of +the existence of the world is, for Hutton, the production of life and +intelligence. + +"We have now considered the globe of this earth as a machine, constructed +upon chemical as well as mechanical principles, by which its different +parts are all adapted, in form, in quality, and in quantity, to a certain +end; an end attained with certainty or success; and an end from which we +may perceive wisdom, in contemplating the means employed. + +"But is this world to be considered thus merely as a machine, to last no +longer than its parts retain their present position, their proper forms +and qualities? Or may it not be also considered as an organised body? +such as has a constitution in which the necessary decay of the machine is +naturally repaired, in the exertion of those productive powers by which +it had been formed. + +"This is the view in which we are now to examine the globe; to see if +there be, in the constitution of this world, a reproductive operation, by +which a ruined constitution may be again repaired, and a duration or +stability thus procured to the machine, considered as a world sustaining +plants and animals."[6] + +[Footnote 6: _Ibid._, vol. i. pp. 16, 17.] + +Kirwan, and the other Philistines of the day, accused Hutton of declaring +that his theory implied that the world never had a beginning, and never +differed in condition from its present state. Nothing could be more +grossly unjust, as he expressly guards himself against any such +conclusion in the following terms:-- + +"But in thus tracing back the natural operations which have succeeded +each other, and mark to us the course of time past, we come to a period +in which we cannot see any farther. This, however, is not the beginning +of the operations which proceed in time and according to the wise economy +of this world; nor is it the establishing of that which, in the course of +time, had no beginning; it is only the limit of our retrospective view of +those operations which have come to pass in time, and have been conducted +by supreme intelligence."[7] + +[Footnote 7: _Ibid._, vol. i. p. 223.] + +I have spoken of Uniformitarianism as the doctrine of Hutton and of +Lyell. If I have quoted the older writer rather than the newer, it is +because his works are little known, and his claims on our veneration too +frequently forgotten, not because I desire to dim the fame of his eminent +successor. Few of the present generation of geologists have read +Playfair's "Illustrations," fewer still the original "Theory of the +Earth"; the more is the pity; but which of us has not thumbed every page +of the "Principles of Geology"? I think that he who writes fairly the +history of his own progress in geological thought, will not be able to +separate his debt to Hutton from his obligations to Lyell; and the +history of the progress of individual geologists is the history of +geology. + + +No one can doubt that the influence of uniformitarian views has been +enormous, and, in the main, most beneficial and favourable to the +progress of sound geology. + +Nor can it be questioned that Uniformitarianism has even a stronger title +than Catastrophism to call itself the geological speculation of Britain, +or, if you will, British popular geology. For it is eminently a British +doctrine, and has even now made comparatively little progress on the +continent of Europe. Nevertheless, it seems to me to be open to serious +criticism upon one of its aspects. + +I have shown how unjust was the insinuation that Hutton denied a +beginning to the world. But it would not be unjust to say that he +persistently in practice, shut his eyes to the existence of that prior +and different state of things which, in theory, he admitted; and, in this +aversion to look beyond the veil of stratified rocks, Lyell follows him. + +Hutton and Lyell alike agree in their indisposition to carry their +speculations a step beyond the period recorded in the most ancient strata +now open to observation in the crust of the earth. This is, for Hutton, +"the point in which we cannot see any farther"; while Lyell tells us,-- + +"The astronomer may find good reasons for ascribing the earth's form to +the original fluidity of the mass, in times long antecedent to the first +introduction of living beings into the planet; but the geologist must be +content to regard the earliest monuments which it is his task to +interpret, as belonging to a period when the crust had already acquired +great solidity and thickness, probably as great as it now possesses, and +when volcanic rocks, not essentially differing from those now produced, +were formed from time to time, the intensity of volcanic heat being +neither greater nor less than it is now."[8] + +[Footnote 8: _Principles of Geology_, vol. ii. p. 211.] + +And again, "As geologists, we learn that it is not only the present +condition of the globe which has been suited to the accommodation of +myriads of living creatures, but that many former states also have been +adapted to the organisation and habits of prior races of beings. The +disposition of the seas, continents and islands, and the climates, have +varied; the species likewise have been changed; and yet they have all +been so modelled, on types analogous to those of existing plants and +animals, as to indicate, throughout, a perfect harmony of design and +unity of purpose. To assume that the evidence of the beginning, or end, +of so vast a scheme lies within the reach of our philosophical inquiries, +or even of our speculations, appears to be inconsistent with a just +estimate of the relations which subsist between the finite powers of man +and the attributes of an infinite and eternal Being."[9] + +[Footnote 9: _Ibid._, vol. ii. p. 613.] + +The limitations implied in these passages appear to me to constitute the +weakness and the logical defect of Uniformitarianism. No one will impute +blame to Hutton that, in face of the imperfect condition, in his day, of +those physical sciences which furnish the keys to the riddles of geology, +he should have thought it practical wisdom to limit his theory to an +attempt to account for "the present order of things"; but I am at a loss +to comprehend why, for all time, the geologist must be content to regard +the oldest fossiliferous rocks as the _ultima Thule_ of his science; or +what there is inconsistent with the relations between the finite and the +infinite mind, in the assumption, that we may discern somewhat of the +beginning, or of the end, of this speck in space we call our earth. The +finite mind is certainly competent to trace out the development of the +fowl within the egg; and I know not on what ground it should find more +difficulty in unravelling the complexities Of the development of the +earth. In fact, as Kant has well remarked,[10] the cosmical process is +really simpler than the biological. + +[Footnote 10: "Man darf es sich also nicht befremden lassen, wenn ich +mich unterstehe zu sagen, dass eher die Bildung aller Himmelskörper, die +Ursache ihrer Bewegungen, kurz der Ursprung der gantzen gegenwärtigen +Verfassung des Weltbaues werden können eingesehen werden, ehe die +Erzeugung eines einzigen Krautes oder einer Raupe aus mechanischen +Gründen, deutlich und vollständig kund werden wird."--KANT'S _Sämmtliche +Werke_, Bd. i. p. 220.] + +This attempt to limit, at a particular point, the progress of inductive +and deductive reasoning from the things which are, to those which were-- +this faithlessness to its own logic, seems to me to have cost +Uniformitarianism the place, as the permanent form of geological +speculation, which it might otherwise have held. + +It remains that I should put before you what I understand to be the third +phase of geological speculation--namely, EVOLUTIONISM. + +I shall not make what I have to say on this head clear, unless I diverge, +or seem to diverge, for a while, from the direct path of my discourse, so +far as to explain what I take to be the scope of geology itself. I +conceive geology to be the history of the earth, in precisely the same +sense as biology is the history of living beings; and I trust you will +not think that I am overpowered by the influence of a dominant pursuit if +I say that I trace a close analogy between these two histories. + +If I study a living being, under what heads does the knowledge I obtain +fall? I can learn its structure, or what we call its ANATOMY; and its +DEVELOPMENT, or the series of changes which it passes through to acquire +its complete structure. Then I find that the living being has certain +powers resulting from its own activities, and the interaction of these +with the activities of other things--the knowledge of which is +PHYSIOLOGY. Beyond this the living being has a position in space and +time, which is its DISTRIBUTION. All these form the body of ascertainable +facts which constitute the _status quo_ of the living creature. But these +facts have their causes; and the ascertainment of these causes is the +doctrine of AETIOLOGY. + +If we consider what is knowable about the earth, we shall find that such +earth-knowledge--if I may so translate the word geology--falls into the +same categories. + +What is termed stratigraphical geology is neither more nor less than the +anatomy of the earth; and the history of the succession of the formations +is the history of a succession of such anatomies, or corresponds with +development, as distinct from generation. + +The internal heat of the earth, the elevation and depression of its +crust, its belchings forth of vapours, ashes, and lava, are its +activities, in as strict a sense as are warmth and the movements and +products of respiration the activities of an animal. The phenomena of the +seasons, of the trade winds, of the Gulf-stream, are as much the results +of the reaction between these inner activities and outward forces, as are +the budding of the leaves in spring and their falling in autumn the +effects of the interaction between the organisation of a plant and the +solar light and heat. And, as the study of the activities of the living +being is called its physiology, so are these phenomena the subject-matter +of an analogous telluric physiology, to which we sometimes give the name +of meteorology, sometimes that of physical geography, sometimes that of +geology. Again, the earth has a place in space and in time, and relations +to other bodies in both these respects, which constitute its +distribution. This subject is usually left to the astronomer; but a +knowledge of its broad outlines seems to me to be an essential +constituent of the stock of geological ideas. + +All that can be ascertained concerning the structure, succession of +conditions, actions, and position in space of the earth, is the matter of +fact of its natural history. But, as in biology, there remains the matter +of reasoning from these facts to their causes, which is just as much +science as the other, and indeed more; and this constitutes geological +aetiology. + +Having regard to this general scheme of geological knowledge and thought, +it is obvious that geological speculation may be, so to speak, anatomical +and developmental speculation, so far as it relates to points of +stratigraphical arrangement which are out of reach of direct observation; +or, it may be physiological speculation so far as it relates to +undetermined problems relative to the activities of the earth; or, it may +be distributional speculation, if it deals with modifications of the +earth's place in space; or, finally, it will be aetiological speculation +if it attempts to deduce the history of the world, as a whole, from the +known properties of the matter of the earth, in the conditions in which +the earth has been placed. + +For the purposes of the present discourse I may take this last to be what +is meant by "geological speculation." + +Now Uniformitarianism, as we have seen, tends to ignore geological +speculation in this sense altogether. + +The one point the catastrophists and the uniformitarians agreed upon, +when this Society was founded, was to ignore it. And you will find, if +you look back into our records, that our revered fathers in geology +plumed themselves a good deal upon the practical sense and wisdom of this +proceeding. As a temporary measure, I do not presume to challenge its +wisdom; but in all organised bodies temporary changes are apt to produce +permanent effects; and as time has slipped by, altering all the +conditions which may have made such mortification of the scientific flesh +desirable, I think the effect of the stream of cold water which has +steadily flowed over geological speculation within these walls has been +of doubtful beneficence. + +The sort of geological speculation to which I am now referring +(geological aetiology, in short) was created, as a science, by that famous +philosopher Immanuel Kant, when, in 1775, he wrote his "General Natural +History and Theory of the Celestial Bodies; or an Attempt to account for +the Constitutional and the Mechanical Origin of the Universe upon +Newtonian principles."[11] + +[Footnote 11: Grant (_History of Physical Astronomy_, p. 574) makes but +the briefest reference to Kant.] + +In this very remarkable but seemingly little-known treatise,[12] Kant +expounds a complete cosmogony, in the shape of a theory of the causes +which have led to the development of the universe from diffused atoms of +matter endowed with simple attractive and repulsive forces. + +[Footnote 12: "Allgemeine Naturgeschichte und Theorie des Himmels; oder +Versuch von der Verfassung und dem mechanischen Ursprunge des ganzen +Weltgebäudes nach Newton'schen Grundsatzen abgehandelt."--KANT'S +_Sämmtliche Werke_, Bd. i. p. 207.] + +"Give me matter," says Kant, "and I will build the world;" and he +proceeds to deduce from the simple data from which he starts, a doctrine +in all essential respects similar to the well-known "Nebular Hypothesis" +of Laplace.[13] He accounts for the relation of the masses and the +densities of the planets to their distances from the sun, for the +eccentricities of their orbits, for their rotations, for their +satellites, for the general agreement in the direction of rotation among +the celestial bodies, for Saturn's ring, and for the zodiacal light. He +finds in each system of worlds, indications that the attractive force of +the central mass will eventually destroy its organisation, by +concentrating upon itself the matter of the whole system; but, as the +result of this concentration, he argues for the development of an amount +of heat which will dissipate the mass once more into a molecular chaos +such as that in which it began. + +[Footnote 13: _Système du Monde_, tome ii. chap. 6.] + +Kant pictures to himself the universe as once an infinite expansion of +formless and diffused matter. At one point of this he supposes a single +centre of attraction set up; and, by strict deductions from admitted +dynamical principles, shows how this must result in the development of a +prodigious central body, surrounded by systems of solar and planetary +worlds in all stages of development. In vivid language he depicts the +great world-maelstrom, widening the margins of its prodigious eddy in the +slow progress of millions of ages, gradually reclaiming more and more of +the molecular waste, and converting chaos into cosmos. But what is gained +at the margin is lost in the centre; the attractions of the central +systems bring their constituents together, which then, by the heat +evolved, are converted once more into molecular chaos. Thus the worlds +that are, lie between the ruins of the worlds that have been, and the +chaotic materials of the worlds that shall be; and in spite of all waste +and destruction, Cosmos is extending his borders at the expense of Chaos. + +Kant's further application of his views to the earth itself is to be +found in his "Treatise on Physical Geography"[14] (a term under which the +then unknown science of geology was included), a subject which he had +studied with very great care and on which he lectured for many years. The +fourth section of the first part of this Treatise is called "History of +the great Changes which the Earth has formerly undergone and is still +undergoing," and is, in fact, a brief and pregnant essay upon the +principles of geology. Kant gives an account first "of the gradual +changes which are now taking place" under the heads of such as are caused +by earthquakes, such as are brought about by rain and rivers, such as are +effected by the sea, such as are produced by winds and frost; and, +finally, such as result from the operations of man. + +[Footnote 14: Kant's _Sämmtliche Werke_, Bd. viii. p. 145.] + +The second part is devoted to the "Memorials of the Changes which the +Earth has undergone in remote Antiquity." These are enumerated as:--A. +Proofs that the sea formerly covered the whole earth. B. Proofs that the +sea has often been changed into dry land and then again into sea. C. A +discussion of the various theories of the earth put forward by +Scheuchzer, Moro, Bonnet, Woodward, White, Leibnitz, Linnaeus, and Buffon. + +The third part contains an "Attempt to give a sound explanation of the +ancient history of the earth." + +I suppose that it would be very easy to pick holes in the details of +Kant's speculations, whether cosmological, or specially telluric, in +their application. But for all that, he seems to me to have been the +first person to frame a complete system of geological speculation by +founding the doctrine of evolution. + +With as much truth as Hutton, Kant could say, "I take things just as I +find them at present, and, from these, I reason with regard to that which +must have been." Like Hutton, he is never tired of pointing out that "in +Nature there is wisdom, system, and consistency." And, as in these great +principles, so in believing that the cosmos has a reproductive operation +"by which a ruined constitution may be repaired," he forestalls Hutton; +while, on the other hand, Kant is true to science. He knows no bounds to +geological speculation but those of the intellect. He reasons back to a +beginning of the present state of things; he admits the possibility of an +end. + +I have said that the three schools of geological speculation which I have +termed Catastrophism, Uniformitarianism, and Evolutionism, are commonly +supposed to be antagonistic to one another; and I presume it will have +become obvious that in my belief, the last is destined to swallow up the +other two. But it is proper to remark that each of the latter has kept +alive the tradition of precious truths. + +CATASTROPHISM has insisted upon the existence of a practically unlimited +bank of force, on which the theorist might draw; and it has cherished the +idea of the development of the earth from a state in which its form, and +the forces which it exerted, were very different from those we now know. +That such difference of form and power once existed is a necessary part +of the doctrine of evolution. + +UNIFORMITARIANISM, on the other hand, has with equal justice insisted +upon a practically unlimited bank of time, ready to discount any quantity +of hypothetical paper. It has kept before our eyes the power of the +infinitely little, time being granted, and has compelled us to exhaust +known causes, before flying to the unknown. + +To my mind there appears to be no sort of necessary theoretical +antagonism between Catastrophism and Uniformitarianism. On the contrary, +it is very conceivable that catastrophes may be part and parcel of +uniformity. Let me illustrate my case by analogy. The working of a clock +is a model of uniform action; good time-keeping means uniformity of +action. But the striking of the clock is essentially a catastrophe; the +hammer might be made to blow up a barrel of gunpowder, or turn on a +deluge of water; and, by proper arrangement, the clock, instead of +marking the hours, might strike at all sorts of irregular periods, never +twice alike, in the intervals, force, or number of its blows. +Nevertheless, all these irregular, and apparently lawless, catastrophes +would be the result of an absolutely uniformitarian action; and we might +have two schools of clock-theorists, one studying the hammer and the +other the pendulum. + +Still less is there any necessary antagonists between either of these +doctrines and that of Evolution, which embraces all that is sound in both +Catastrophism and Uniformitarianism, while it rejects the arbitrary +assumptions of the one and the, as arbitrary, limitations of the other. +Nor is the value of the doctrine of Evolution to the philosophic thinker +diminished by the fact that it applies the same method to the living and +the not-living world; and embraces, in one stupendous analogy, the growth +of a solar system from molecular chaos, the shaping of the earth from the +nebulous cub-hood of its youth, through innumerable changes and +immeasurable ages, to its present form; and the development of a living +being from the shapeless mass of protoplasm we term a germ. + +I do not know whether Evolutionism can claim that amount of currency +which would entitle it to be called British popular geology; but, more or +less vaguely, it is assuredly present in the minds of most geologists. + +Such being the three phases of geological speculation, we are now in +position to inquire which of these it is that Sir William Thomson calls +upon us to reform in the passages which I have cited. + +It is obviously Uniformitarianism which the distinguished physicist takes +to be the representative of geological speculation in general. And thus a +first issue is raised, inasmuch as many persons (and those not the least +thoughtful among the younger geologists) do not accept strict +Uniformitarianism as the final form of geological speculation. We should +say, if Hutton and Playfair declare the course of the world to have been +always the same, point out the fallacy by all means; but, in so doing, do +not imagine that you are proving modern geology to be in opposition to +natural philosophy. I do not suppose that, at the present day, any +geologist would be found to maintain absolute Uniformitarianism, to deny +that the rapidity of the rotation of the earth _may_ be diminishing, that +the sun _may_ be waxing dim, or that the earth itself _may_ be cooling. +Most of us, I suspect, are Gallios, "who care for none of these things," +being of opinion that, true or fictitious, they have made no practical +difference to the earth, during the period of which a record is preserved +in stratified deposits. + +The accusation that we have been running counter to the _principles_ of +natural philosophy, therefore, is devoid of foundation. The only question +which can arise is whether we have, or have not, been tacitly making +assumptions which are in opposition to certain conclusions which may be +drawn from those principles. And this question subdivides itself into +two:--the first, are we really contravening such conclusions? the second, +if we are, are those conclusions so firmly based that we may not +contravene them? I reply in the negative to both these questions, and I +will give you my reasons for so doing. Sir William Thomson believes that +he is able to prove, by physical reasonings, "that the existing state of +things on the earth, life on the earth--all geological history showing +continuity of life--must be limited within some such period of time as +one hundred million years" (_loc. cit._ p. 25). + +The first inquiry which arises plainly is, has it ever been denied that +this period _may_ be enough for the purposes of geology? + +The discussion of this question is greatly embarrassed by the vagueness +with which the assumed limit is, I will not say defined, but indicated,-- +"some such period of past time as one hundred million years." Now does +this mean that it may have been two, or three, or four hundred million +years? Because this really makes all the difference.[15] + +[Footnote 15: Sir William Thomson implies (_loc. cit_. p. 16) that the +precise time is of no consequence: "the principle is the same"; but, as +the principle is admitted, the whole discussion turns on its practical +results.] + +I presume that 100,000 feet may be taken as a full allowance for the +total thickness of stratified rocks containing traces of life; 100,000 +divided by 100,000,000 = 0.001. Consequently, the deposit of 100,000 feet +of stratified rock in 100,000,000 years means that the deposit has taken +place at the rate of 1/1000 of a foot, or, say, 1/83 of an inch, per +annum. + +Well, I do not know that any one is prepared to maintain that, even +making all needful allowances, the stratified rocks may not have been +formed, on the average, at the rate of 1/83 of an inch per annum. I +suppose that if such could be shown to be the limit of world-growth, we +could put up with the allowance without feeling that our speculations had +undergone any revolution. And perhaps, after all, the qualifying phrase +"some such period" may not necessitate the assumption of more than 1/166 +or 1/249 or 1/332 of an inch of deposit per year, which, of course, would +give us still more ease and comfort. + +But, it may be said, that it is biology, and not geology, which asks for +so much time--that the succession of life demands vast intervals; but +this appears to me to be reasoning in a circle. Biology takes her time +from geology. The only reason we have for believing in the slow rate of +the change in living forms is the fact that they persist through a series +of deposits which, geology informs us, have taken a long while to make. +If the geological clock is wrong, all the naturalist will have to do is +to modify his notions of the rapidity of change accordingly. And I +venture to point out that, when we are told that the limitation of the +period during which living beings have inhabited this planet to one, two, +or three hundred million years requires a complete revolution in +geological speculation, the _onus probandi_ rests on the maker of the +assertion, who brings forward not a shadow of evidence in its support. + +Thus, if we accept the limitation of time placed before us by Sir W. +Thomson, it is not obvious, on the face of the matter, that we shall have +to alter, or reform, our ways in any appreciable degree; and we may +therefore proceed with much calmness, and indeed much indifference, as to +the result, to inquire whether that limitation is justified by the +arguments employed in its support. + +These arguments are three in number.-- + +I. The first is based upon the undoubted fact that the tides tend to +retard the rate of the earth's rotation upon its axis. That this must be +so is obvious, if one considers, roughly, that the tides result from the +pull which the sun and the moon exert upon the sea, causing it to act as +a sort of break upon the rotating solid earth. + +Kant, who was by no means a mere "abstract philosopher," but a good +mathematician and well versed in the physical science of his time, not +only proved this in an essay of exquisite clearness and intelligibility, +now more than a century old,[16] but deduced from it some of its more +important consequences, such as the constant turning of one face of the +moon towards the earth. + +[Footnote 16: "Untersuchung der Frage oh die Erde in ihrer Umdrehung um +die Achse, wodurch sie die Abwechselung des Tages und der Nacht +hervorbringt, einige Veränderung seit den ersten Zeiten ihres Ursprunges +erlitten habe, &c."--KANT's _Sämmntliche Werke_, Bd. i. p. 178.] + +But there is a long step from the demonstration of a tendency to the +estimation of the practical value of that tendency, which is all with +which we are at present concerned. The facts bearing on this point appear +to stand as follows:-- + +It is a matter of observation that the moon's mean motion is (and has for +the last 3,000 years been) undergoing an acceleration, relatively to the +rotation of the earth. Of course this may result from one of two causes: +the moon may really have been moving more swiftly in its orbit; or the +earth may have been rotating more slowly on its axis. + +Laplace believed he had accounted for this phenomenon by the fact that +the eccentricity of the earth's orbit has been diminishing throughout +these 3,000 years. This would produce a diminution of the mean attraction +of the sun on the moon; or, in other words, an increase in the attraction +of the earth on the moon; and, consequently, an increase in the rapidity +of the orbital motion of the latter body. Laplace, therefore, laid the +responsibility of the acceleration upon the moon, and if his views were +correct, the tidal retardation must either be insignificant in amount, or +be counteracted by some other agency. + +Our great astronomer, Adams, however, appears to have found a flaw in +Laplace's calculation, and to have shown that only half the observed +retardation could be accounted for in the way he had suggested. There +remains, therefore, the other half to be accounted for; and here, in the +absence of all positive knowledge, three sets of hypotheses have been +suggested. + +(_a_.) M. Delaunay suggests that the earth is at fault, in consequence of +the tidal retardation. Messrs. Adams, Thomson, and Tait work out this +suggestion, and, "on a certain assumption as to the proportion of +retardations due to the sun and moon," find the earth may lose twenty-two +seconds of time in a century from this cause.[17] + +[Footnote 17: Sir W. Thomson, _loc. cit_. p. 14.] + +(_b_.) But M. Dufour suggests that the retardation of the earth (which is +hypothetically assumed to exist) may be due in part, or wholly, to the +increase of the moment of inertia of the earth by meteors falling upon +its surface. This suggestion also meets with the entire approval of Sir +W. Thomson, who shows that meteor-dust, accumulating at the rate of one +foot in 4,000 years, would account for the remainder of retardation.[18] + +[Footnote 18: _Ibid._ p. 27.] + +(_c_.) Thirdly, Sir W. Thomson brings forward an hypothesis of his own +with respect to the cause of the hypothetical retardation of the earth's +rotation:-- + +"Let us suppose ice to melt from the polar regions (20° round each pole, +we may say) to the extent of something more than a foot thick, enough to +give 1.1 foot of water over those areas, or 0.006 of a foot of water if +spread over the whole globe, which would, in reality, raise the sea-level +by only some such undiscoverable difference as three-fourths of an inch +or an inch. This, or the reverse, which we believe might happen any year, +and could certainly not be detected without far more accurate +observations and calculations for the mean sea-level than any hitherto +made, would slacken or quicken the earth's rate as a timekeeper by one- +tenth of a second per year."[19] + +[Footnote 19: _Ibid._] + +I do not presume to throw the slightest doubt upon the accuracy of any of +the calculations made by such distinguished mathematicians as those who +have made the suggestions I have cited. On the contrary, it is necessary +to my argument to assume that they are all correct. But I desire to point +out that this seems to be one of the many cases in which the admitted +accuracy of mathematical process is allowed to throw a wholly +inadmissible appearance of authority over the results obtained by them. +Mathematics may be compared to a mill of exquisite workmanship, which +grinds you stuff of any degree of fineness; but, nevertheless, what you +get out depends upon what you put in; and as the grandest mill in the +world will not extract wheat-flour from peascods, so pages of formulae +will not get a definite result out of loose data. + +In the present instance it appears to be admitted:-- + +1. That it is not absolutely certain, after all, whether the moon's mean +motion is undergoing acceleration, or the earth's rotation +retardation.[20] And yet this is the key of the whole position. + +[Footnote 20: It will be understood that I do not wish to deny that the +earth's rotation _may be_ undergoing retardation.] + +2. If the rapidity of the earth's rotation is diminishing, it is not +certain how much of that retardation is due to tidal friction, how much +to meteors, how much to possible excess of melting over accumulation of +polar ice, during the period covered by observation, which amounts, at +the outside, to not more than 2,600 years. + +3. The effect of a different distribution of land and water in modifying +the retardation caused by tidal friction, and of reducing it, under some +circumstances, to a minimum, does not appear to be taken into account. + +4. During the Miocene epoch the polar ice was certainly many feet thinner +than it has been during, or since, the Glacial epoch. Sir W. Thomson +tells us that the accumulation of something more than a foot of ice +around the poles (which implies the withdrawal of, say, an inch of water +from the general surface of the sea) will cause the earth to rotate +quicker by one-tenth of a second per annum. It would appear, therefore, +that the earth may have been rotating, throughout the whole period which +has elapsed from the commencement of the Glacial epoch down to the +present time, one, or more, seconds per annum quicker than it rotated +during the Miocene epoch. + +But, according to Sir W. Thomson's calculation, tidal retardation will +only account for a retardation of 22" in a century, or 22/100 (say 1/5) +of a second per annum. + +Thus, assuming that the accumulation of polar ice since the Miocene epoch +has only been sufficient to produce ten times the effect of a coat of ice +one foot thick, we shall have an accelerating cause which covers all the +loss from tidal action, and leaves a balance of 4/5 of a second per annum +in the way of acceleration. + +If tidal retardation can be thus checked and overthrown by other +temporary conditions, what becomes of the confident assertion, based upon +the assumed uniformity of tidal retardation, that ten thousand million +years ago the earth must have been rotating more than twice as fast as at +present, and, therefore, that we geologists are "in direct opposition to +the principles of Natural Philosophy" if we spread geological history +over that time? + +II. The second argument is thus stated by Sir W. Thomson:--"An article, +by myself, published in 'Macmillan's Magazine' for March 1862, on the age +of the sun's heat, explains results of investigation into various +questions as to possibilities regarding the amount of heat that the sun +could have, dealing with it as you would with a stone, or a piece of +matter, only taking into account the sun's dimensions, which showed it to +be possible that the sun may have already illuminated the earth for as +many as one hundred million years, but at the same time rendered it +almost certain that he had not illuminated the earth for five hundred +millions of years. The estimates here are necessarily very vague; but +yet, vague as they are, I do not know that it is possible, upon any +reasonable estimate founded on known properties of matter, to say that we +can believe the sun has really illuminated the earth for five hundred +million years."[21] + +[Footnote 21: _Loc. cit._ p. 20.] + +I do not wish to "Hansardise" Sir William Thomson by laying much stress +on the fact that, only fifteen years ago he entertained a totally +different view of the origin of the sun's heat, and believed that the +energy radiated from year to year was supplied from year to year--a +doctrine which would have suited Hutton perfectly. But the fact that so +eminent a physical philosopher has, thus recently, held views opposite to +those which he now entertains, and that he confesses his own estimates to +be "very vague," justly entitles us to disregard those estimates, if any +distinct facts on our side go against them. However, I am not aware that +such facts exist. As I have already said, for anything I know, one, two, +or three hundred millions of years may serve the needs of geologists +perfectly well. + +III. The third line of argument is based upon the temperature of the +interior of the earth. Sir W. Thomson refers to certain investigations +which prove that the present thermal condition of the interior of the +earth implies either a heating of the earth within the last 20,000 years +of as much as 100° F., or a greater heating all over the surface at some +time further back than 20,000 years, and then proceeds thus:-- + +"Now, are geologists prepared to admit that, at some time within the last +20,000 years, there has been all over the earth so high a temperature as +that? I presume not; no geologist--no _modern_ geologist--would for a +moment admit the hypothesis that the present state of underground heat is +due to a heating of the surface at so late a period as 20,000 years ago. +If that is not admitted we are driven to a greater heat at some time more +than 20,000 years ago. A greater heating all over the surface than 100° +Fahrenheit would kill nearly all existing plants and animals, I may +safely say. Are modern geologists prepared to say that all life was +killed off the earth 50,000, 100,000, or 200,000 years ago? For the +uniformity theory, the further back the time of high surface-temperature +is put the better; but the further back the time of heating, the hotter +it must have been. The best for those who draw most largely on time is +that which puts it furthest back; and that is the theory that the heating +was enough to melt the whole. But even if it was enough to melt the +whole, we must still admit some limit, such as fifty million years, one +hundred million years, or two or three hundred million years ago. Beyond +that we cannot go."[22] + +[Footnote 22: _Loc. cit._ p. 24.] + +It will be observed that the "limit" is once again of the vaguest, +ranging from 50,000,000 years to 300,000,000. And the reply is, once +more, that, for anything that can be proved to the contrary, one or two +hundred million years might serve the purpose, even of a thoroughgoing +Huttonian uniformitarian, very well. + +But if, on the other hand, the 100,000,000 or 200,000,000 years appear to +be insufficient for geological purposes, we must closely criticise the +method by which the limit is reached. The argument is simple enough. +_Assuming_ the earth to be nothing but a cooling mass, the quantity of +heat lost per year, _supposing_ the rate of cooling to have been uniform, +multiplied by any given number of years, will be given the minimum +temperature that number of years ago. + +But is the earth nothing but a cooling mass, "like a hot-water jar such +as is used in carriages," or "a globe of sandstone," and has its cooling +been uniform? An affirmative answer to both these questions seems to be +necessary to the validity of the calculations on which Sir W. Thomson +lays so much stress. + +Nevertheless it surely may be urged that such affirmative answers are +purely hypothetical, and that other suppositions have an equal right to +consideration. + +For example, is it not possible that, at the prodigious temperature which +would seem to exist at 100 miles below the surface, all the metallic +bases may behave as mercury does at a red heat, when it refuses to +combine with oxygen; while, nearer the surface, and therefore at a lower +temperature, they may enter into combination (as mercury does with oxygen +a few degrees below its boiling-point), and so give rise to a heat +totally distinct from that which they possess as cooling bodies? And has +it not also been proved by recent researches that the quality of the +atmosphere may immensely affect its permeability to heat; and, +consequently, profoundly modify the rate of cooling the globe as a whole? + +I do not think it can be denied that such conditions may exist, and may +so greatly affect the supply, and the loss, of terrestrial heat as to +destroy the value of any calculations which leave them out of sight. + +My functions as your advocate are at an end. I speak with more than the +sincerity of a mere advocate when I express the belief that the case +against us has entirely broken down. The cry for reform which has been +raised without, is superfluous, inasmuch as we have long been reforming +from within, with all needful speed. And the critical examination of the +grounds upon which the very grave charge of opposition to the principles +of Natural Philosophy has been brought against us, rather shows that we +have exercised a wise discrimination in declining, for the present, to +meddle with our foundations. + + + +XI + + +PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION + +[1870] + +It is now eight years since, in the absence of the late Mr. Leonard +Horner, who then presided over us, it fell to my lot, as one of the +Secretaries of this Society, to draw up the customary Annual Address. I +availed myself of the opportunity to endeavour to "take stock" of that +portion of the science of biology which is commonly called +"palaeontology," as it then existed; and, discussing one after another the +doctrines held by palaeontologists, I put before you the results of my +attempts to sift the well-established from the hypothetical or the +doubtful. Permit me briefly to recall to your minds what those results +were:-- + +1. The living population of all parts of the earth's surface which have +yet been examined has undergone a succession of changes which, upon the +whole, have been of a slow and gradual character. + +2. When the fossil remains which are the evidences of these successive +changes, as they have occurred in any two more or less distant parts of +the surface of the earth, are compared, they exhibit a certain broad and +general parallelism. In other words, certain forms of life in one +locality occur in the same general order of succession as, or are +_homotaxial_ with, similar forms in the other locality. + +3. Homotaxis is not to be held identical with synchronism without +independent evidence. It is possible that similar, or even identical, +faunae and florae in two different localities may be of extremely different +ages, if the term "age" is used in its proper chronological sense. I +stated that "geographical provinces, or zones, may have been as +distinctly marked in the Palaeozoic epoch as at present; and those +seemingly sudden appearances of new genera and species which we ascribe +to new creation, may be simple results of migration." + +4. The opinion that the oldest known fossils are the earliest forms of +life has no solid foundation. + +5. If we confine ourselves to positively ascertained facts, the total +amount of change in the forms of animal and vegetable life, since the +existence of such forms is recorded, is small. When compared with the +lapse of time since the first appearance of these forms, the amount of +change is wonderfully small. Moreover, in each great group of the animal +and vegetable kingdoms, there are certain forms which I termed PERSISTENT +TYPES, which have remained, with but very little apparent change, from +their first appearance to the present time. + +6. In answer to the question "What, then, does an impartial survey of the +positively ascertained truths of palaeontology testify in relation to the +common doctrines of progressive modification, which suppose that +modification to have taken place by a necessary progress from more to +less embryonic forms, from more to less generalised types, within the +limits of the period represented by the fossiliferous rocks?" I reply, +"It negatives these doctrines; for it either shows us no evidence of such +modification, or demonstrates such modification as has occurred to have +been very slight; and, as to the nature of that modification, it yields +no evidence whatsoever that the earlier members of any long-continued +group were more generalised in structure than the later ones." + +I think that I cannot employ my last opportunity of addressing you, +officially, more properly--I may say more dutifully--than in revising +these old judgments with such help as further knowledge and reflection, +and an extreme desire to get at the truth, may afford me. + +1. With respect to the first proposition, I may remark that whatever may +be the case among the physical geologists, catastrophic palaeontologists +are practically extinct. It is now no part of recognised geological +doctrine that the species of one formation all died out and were replaced +by a brand-new set in the next formation. On the contrary, it is +generally, if not universally, agreed that the succession of life has +been the result of a slow and gradual replacement of species by species; +and that all appearances of abruptness of change are due to breaks in the +series of deposits, or other changes in physical conditions. The +continuity of living forms has been unbroken from the earliest times to +the present day. + +2, 3. The use of the word "homotaxis" instead of "synchronism" has not, +so far as I know, found much favour in the eyes of geologists. I hope, +therefore, that it is a love for scientific caution, and not mere +personal affection for a bantling of my own, which leads me still to +think that the change of phrase is of importance, and that the sooner it +is made, the sooner shall we get rid of a number of pitfalls which beset +the reasoner upon the facts and theories of geology. + +One of the latest pieces of foreign intelligence which has reached us is +the information that the Austrian geologists have, at last, succumbed to +the weighty evidence which M. Barrande has accumulated, and have admitted +the doctrine of colonies. But the admission of the doctrine of colonies +implies the further admission that even identity of organic remains is no +proof of the synchronism of the deposits which contain them. + +4. The discussions touching the _Eozoon,_ which commenced in 1864, have +abundantly justified the fourth proposition. In 1862, the oldest record +of life was in the Cambrian rocks; but if the _Eozoon_ be, as Principal +Dawson and Dr. Carpenter have shown so much reason for believing, the +remains of a living being, the discovery of its true nature carried life +back to a period which, as Sir William Logan has observed, is as remote +from that during which the Cambrian rocks were deposited, as the Cambrian +epoch itself is from the tertiaries. In other words, the ascertained +duration of life upon the globe was nearly doubled at a stroke. + +5. The significance of persistent types, and of the small amount of +change which has taken place even in those forms which can be shown to +have been modified, becomes greater and greater in my eyes, the longer I +occupy myself with the biology of the past. + +Consider how long a time has elapsed since the Miocene epoch. Yet, at +that time there is reason to believe that every important group in every +order of the _Mammalia_ was represented. Even the comparatively scanty +Eocene fauna yields examples of the orders _Cheiroptera, Insectivora, +Rodentia_, and _Perissodactyla_; of _Artiodactyla_ under both the +Ruminant and the Porcine modifications; of _Caranivora, Cetacea_, and +_Marsupialia_. + +Or, if we go back to the older half of the Mesozoic epoch, how truly +surprising it is to find every order of the _Reptilia_, except the +_Ophidia_, represented; while some groups, such as the _Ornithoseclida_ +and the _Pterosauria_, more specialised than any which now exist, +abounded. + +There is one division of the _Amphibia_ which offers especially important +evidence upon this point, inasmuch as it bridges over the gap between the +Mesozoic and the Palaeozoic formations (often supposed to be of such +prodigious magnitude), extending, as it does, from the bottom of the +Carboniferous series to the top of the Trias, if not into the Lias. I +refer to the Labyrinthodonts. As the Address of 1862 was passing through +the press, I was able to mention, in a note, the discovery of a large +Labyrinthodont, with well-ossified vertebrae, in the Edinburgh coal-field. +Since that time eight or ten distinct genera of Labyrinthodonts have been +discovered in the Carboniferous rocks of England, Scotland, and Ireland, +not to mention the American forms described by Principal Dawson and +Professor Cope. So that, at the present time, the Labyrinthodont Fauna of +the Carboniferous rocks is more extensive and diversified than that of +the Trias, while its chief types, so far as osteology enables us to +judge, are quite as highly organised. Thus it is certain that a +comparatively highly organised vertebrate type, such as that of the +Labyrinthodonts, is capable of persisting, with no considerable change, +through the period represented by the vast deposits which constitute the +Carboniferous, the Permian, and the Triassic formations. + +The very remarkable results which have been brought to light by the +sounding and dredging operations, which have been carried on with such +remarkable success by the expeditions sent out by our own, the American, +and the Swedish Governments, under the supervision of able naturalists, +have a bearing in the same direction. These investigations have +demonstrated the existence, at great depths in the ocean, of living +animals in some cases identical with, in others very similar to, those +which are found fossilised in the white chalk. The _Globigerinoe_, +Cyatholiths, Coccospheres, Discoliths in the one are absolutely identical +with those in the other; there are identical, or closely analogous, +species of Sponges, Echinoderms, and Brachiopods. Off the coast of +Portugal, there now lives a species of _Beryx_, which, doubtless, leaves +its bones and scales here and there in the Atlantic ooze, as its +predecessor left its spoils in the mud of the sea of the Cretaceous +epoch. + +Many years ago[1] I ventured to speak of the Atlantic mud as "modern +chalk," and I know of no fact inconsistent with the view which Professor +Wyville Thomson has advocated, that the modern chalk is not only the +lineal descendant of the ancient chalk, but that it remains, so to speak, +in the possession of the ancestral estate; and that from the Cretaceous +period (if not much earlier) to the present day, the deep sea has covered +a large part of what is now the area of the Atlantic. But if +_Globigerina_, and _Terebratula caput-serpentis_ and _Beryx_, not to +mention other forms of animals and of plants, thus bridge over the +interval between the present and the Mesozoic periods, is it possible +that the majority of other living things underwent a "sea-change into +something new and strange" all at once? + +[Footnote 1: See an article in the _Saturday Review_, for 1858, on +"Chalk, Ancient and Modern."] + +6. Thus far I have endeavoured to expand and to enforce by fresh +arguments, but not to modify in any important respect, the ideas +submitted to you on a former occasion. But when I come to the +propositions touching progressive modification, it appears to me, with +the help of the new light which has broken from various quarters, that +there is much ground for softening the somewhat Brutus-like severity with +which, in 1862, I dealt with a doctrine, for the truth of which I should +have been glad enough to be able to find a good foundation. So far, +indeed, as the _Invertebrata_ and the lower _Vertebrata_ are concerned, +the facts and the conclusions which are to be drawn from them appear to +me to remain what they were. For anything that, as yet, appears to the +contrary, the earliest known Marsupials may have been as highly organised +as their living congeners; the Permian lizards show no signs of +inferiority to those of the present day; the Labyrinthodonts cannot be +placed below the living Salamander and Triton; the Devonian Ganoids are +closely related to _Polypterus_ and to _Lepidosiren_. + +But when we turn to the higher _Vertebrata_, the results of recent +investigations, however we may sift and criticise them, seem to me to +leave a clear balance in favour of the doctrine of the evolution of +living forms one from another. Nevertheless, in discussing this question, +it is very necessary to discriminate carefully between the different +kinds of evidence from fossil remains which are brought forward in favour +of evolution. + +Every fossil which takes an intermediate place between forms of life +already known, may be said, so far as it is intermediate, to be evidence +in favour of evolution, inasmuch as it shows a possible road by which +evolution may have taken place. But the mere discovery of such a form +does not, in itself, prove that evolution took place by and through it, +nor does it constitute more than presumptive evidence in favour of +evolution in general. Suppose A, B, C to be three forms, while B is +intermediate in structure between A and C. Then the doctrine of evolution +offers four possible alternatives. A may have become C by way of B; or C +may have become A by way of B; or A and C may be independent +modifications of B; or A, B, and C may be independent modifications of +some unknown D. Take the case of the Pigs, the _Anoplothcridoe_, and the +Ruminants. The _Anoplothcridoe_ are intermediate between the first and +the last; but this does not tell us whether the Ruminants have come from +the Pigs, or the Pigs from Ruminants, or both from _Anoplothcridoe_, or +whether Pigs, Ruminants, and _Anoplotlicridoe_ alike may not have +diverged from some common stock. + +But if it can be shown that A, B, and C exhibit successive stages in the +degree of modification, or specialisation, of the same type; and if, +further, it can be proved that they occur in successively newer deposits, +A being in the oldest and C in the newest, then the intermediate +character of B has quite another importance, and I should accept it, +without hesitation, as a link in the genealogy of C. I should consider +the burden of proof to be thrown upon any one who denied C to have been +derived from A by way of B, or in some closely analogous fashion; for it +is always probable that one may not hit upon the exact line of filiation, +and, in dealing with fossils, may mistake uncles and nephews for fathers +and sons. + +I think it necessary to distinguish between the former and the latter +classes of intermediate forms, as _intercalary types_ and _linear types_. +When I apply the former term, I merely mean to say that as a matter of +fact, the form B, so named, is intermediate between the others, in the +sense in which the _Anoplotherium_ is intermediate between the Pigs and +the Ruminants--without either affirming, or denying, any direct genetic +relation between the three forms involved. When I apply the latter term, +on the other hand, I mean to express the opinion that the forms A, B, and +C constitute a line of descent, and that B is thus part of the lineage of +C. + +From the time when Cuvier's wonderful researches upon the extinct Mammals +of the Paris gypsum first made intercalary types known, and caused them +to be recognised as such, the number of such forms has steadily increased +among the higher _Mammalia_. Not only do we now know numerous intercalary +forins of _Ungulata_, but M. Gaudry's great monograph upon the fossils of +Pikermi (which strikes me as one of the most perfect pieces of +palaeontological work I have seen for a long time) shows us, among the +Primates, _Mesopithecus_ as an intercalary form between the +_Semnopitheci_ and the _Macaci_; and among the _Carnivora_, _Hyoenictis_ +and _Ictitherium_ as intercalary, or, perhaps, linear types between the +_Viverridoe_ and the _Hyoenidoe_. + +Hardly any order of the higher _Mammalia_ stands so apparently separate +and isolated from the rest as that of the _Cetacea_; though a careful +consideration of the structure of the pinnipede _Carnivora_, or Seals, +shows, in them, many an approximation towards the still more completely +marine mammals. The extinct _Zeuglodon_, however, presents us with an +intercalary form between the type of the Seals and that of the Whales. +The skull of this great Eocene sea-monster, in fact, shows by the narrow +and prolonged interorbital region; the extensive union of the parietal +bones in a sagittal suture; the well-developed nasal bones; the distinct +and large incisors implanted in premaxillary bones, which take a full +share in bounding the fore part of the gape; the two-fanged molar teeth +with triangular and serrated crowns, not exceeding five on each side in +each jaw; and the existence of a deciduous dentition--its close relation +with the Seals. While, on the other hand, the produced rostral form of +the snout, the long symphysis, and the low coronary process of the +mandible are approximations to the cetacean form of those parts. + +The scapula resembles that of the cetacean _Hyperoodon_, but the supra- +spinous fossa is larger and more seal-like; as is the humerus, which +differs from that of the _Cetacea_ in presenting true articular surfaces +for the free jointing of the bones of the fore-arm. In the apparently +complete absence of hinder limbs, and in the characters of the vertebral +column, the _Zeuglodon_ lies on the cetacean side of the boundary line; +so that upon the whole, the Zeuglodonts, transitional as they are, are +conveniently retained in the cetacean order. And the publication, in +1864, of M. Van Beneden's memoir on the Miocene and Pliocene _Squalodon_, +furnished much better means than anatomists previously possessed of +fitting in another link of the chain which connects the existing +_Cetacea_ with _Zeuglodon_. The teeth are much more numerous, although +the molars exhibit the zeuglodont double fang; the nasal bones are very +short, and the upper surface of the rostrum presents the groove, filled +up during life by the prolongation of the ethmoidal cartilage, which is +so characteristic of the majority of the _Cetacea_. + +It appears to me that, just as among the existing _Carnivora_, the +walruses and the eared seals are intercalary forms between the fissipede +Carnivora and the ordinary seals, so the Zeuglodonts are intercalary +between the _Carnivora_, as a whole, and the _Cetacea_. Whether the +Zeuglodonts are also linear types in their relation to these two groups +cannot be ascertained, until we have more definite knowledge than we +possess at present, respecting the relations in time of the _Carnivora_ +and _Cetacea_. + +Thus far we have been concerned with the intercalary types which occupy +the intervals between Families or Orders of the same class; but the +investigations which have been carried on by Professor Gegenbaur, +Professor Cope, and myself into the structure and relations of the +extinct reptilian forms of the _Ornithoscelida_ (or _Dinosauria_ and +_Compsognatha_) have brought to light the existence of intercalary forms +between what have hitherto been always regarded as very distinct classes +of the vertebrate sub-kingdom, namely _Reptilia_ and _Aves_. Whatever +inferences may, or may not, be drawn from the fact, it is now an +established truth that, in many of these _Ornithoscelida_, the hind limbs +and the pelvis are much more similar to those of Birds than they are to +those of Reptiles, and that these Bird-reptiles, or Reptile-birds, were +more or less completely bipedal. + +When I addressed you in 1862, I should have been bold indeed had I +suggested that palaeontology would before long show us the possibility of +a direct transition from the type of the lizard to that of the ostrich. +At the present moment, we have, in the _Ornithoscelida_, the intercalary +type, which proves that transition to be something more than a +possibility; but it is very doubtful whether any of the genera of +_Ornithoscelida_ with which we are at present acquainted are the actual +linear types by which the transition from the lizard to the bird was +effected. These, very probably, are still hidden from us in the older +formations. + +Let us now endeavour to find some cases of true linear types, or forms +which are intermediate between others because they stand in a direct +genetic relation to them. It is no easy matter to find clear and +unmistakable evidence of filiation among fossil animals; for, in order +that such evidence should be quite satisfactory, it is necessary that we +should be acquainted with all the most important features of the +organisation of the animals which are supposed to be thus related, and +not merely with the fragments upon which the genera and species of the +palaeontologist are so often based. M. Gaudry has arranged the species of +_Hyoenidoe, Proboscidea, Rhinocerotidoe_, and _Equidoe_ in their order of +filiation from their earliest appearance in the Miocene epoch to the +present time, and Professor Rütimeyer has drawn up similar schemes for +the Oxen and other _Ungulata_--with what, I am disposed to think, is a +fair and probable approximation to the order of nature. But, as no one is +better aware than these two learned, acute, and philosophical biologists, +all such arrangements must be regarded as provisional, except in those +cases in which, by a fortunate accident, large series of remains are +obtainable from a thick and widespread series of deposits. It is easy to +accumulate probabilities--hard to make out some particular case in such a +way that it will stand rigorous criticism. + +After much search, however, I think that such a case is to be made out in +favour of the pedigree of the Horses. + +The genus _Equus_ is represented as far back as the latter part of the +Miocene epoch; but in deposits belonging to the middle of that epoch its +place is taken by two other genera, _Hipparion_ and _Anchitherium_;[2] +and, in the lowest Miocene and upper Eocene, only the last genus occurs. +A species of _Anchitherium_ was referred by Cuvier to the _Paloeotheria_ +under the name of _P. aurelianense_. The grinding-teeth are in fact very +similar in shape and in pattern, and in the absence of any thick layer of +cement, to those of some species of _Paloeotherium_, especially Cuvier's +_Paloeotherium minus_, which has been formed into a separate genus, +_Plagiolophus_, by Pomel. But in the fact that there are only six full- +sized grinders in the lower jaw, the first premolar being very small; +that the anterior grinders are as large as, or rather larger than, the +posterior ones; that the second premolar has an anterior prolongation; +and that the posterior molar of the lower jaw has, as Cuvier pointed out, +a posterior lobe of much smaller size and different form, the dentition +of _Anchitherium_ departs from the type of the _Paloeotherium_, and +approaches that of the Horse. + +[Footnote 2: Hermann von Meyer gave the name of _Anchitherium_ to _A. +Ezquerroe_; and in his paper on the subject he takes great pains to +distinguish the latter as the type of a new genus, from Cuvier's +_Paloeotherium d'Orléans_. But it is precisely the _Paloeotherium +d'Orléans_ which is the type of Christol's genus _Hipparitherium_; and +thus, though _Hipparitherium_ is of later date than _Anchitherium_, it +seemed to me to have a sort of equitable right to recognition when this +Address was written. On the whole, however, it seems most convenient to +adopt _Anchitherium_.] + +Again, the skeleton of _Anchitherium_ is extremely equine. M. Christol +goes so far as to say that the description of the bones of the horse, or +the ass, current in veterinary works, would fit those of _Anchitherium_. +And, in a general way, this may be true enough; but there are some most +important differences, which, indeed, are justly indicated by the same +careful observer. Thus the ulna is complete throughout, and its shaft is +not a mere rudiment, fused into one bone with the radius. There are three +toes, one large in the middle and one small on each side. The femur is +quite like that of a horse, and has the characteristic fossa above the +external condyle. In the British Museum there is a most instructive +specimen of the leg-bones, showing that the fibula was represented by the +external malleolus and by a flat tongue of bone, which extends up from it +on the outer side of the tibia, and is closely ankylosed with the latter +bone.[3] The hind toes are three, like those of the fore leg; and the +middle metatarsal bone is much less compressed from side to side than +that of the horse. + +[Footnote 3: I am indebted to M. Gervais for a specimen which indicates +that the fibula was complete, at any rate, in some cases; and for a very +interesting ramps of a mandible, which shows that, as in the +_Paloeotheria_, the hindermost milk-molar of the lower jaw was devoid of +the posterior lobe which exists in the hindermost true molar.] + +In the _Hipparion_, the teeth nearly resemble those of the Horses, though +the crowns of the grinders are not so long; like those of the Horses, +they are abundantly coated with cement. The shaft of the ulna is reduced +to a mere style, ankylosed throughout nearly its whole length with the +radius, and appearing to be little more than a ridge on the surface of +the latter bone until it is carefully examined. The front toes are still +three, but the outer ones are more slender than in _Anchitherium_, and +their hoofs smaller in proportion to that of the middle toe; they are, in +fact, reduced to mere dew-claws, and do not touch the ground. In the leg, +the distal end of the fibula is so completely united with the tibia that +it appears to be a mere process of the latter bone, as in the Horses. + +In _Equus_, finally, the crowns of the grinding-teeth become longer, and +their patterns are slightly modified; the middle of the shaft of the ulna +usually vanishes, and its proximal and distal ends ankylose with the +radius. The phalanges of the two outer toes in each foot disappear, their +metacarpal and metatarsal bones being left as the "splints." + +The _Hipparion_ has large depressions on the face in front of the orbits, +like those for the "larmiers" of many ruminants; but traces of these are +to be seen in some of the fossil horses from the Sewalik Hills; and, as +Leidy's recent researches show, they are preserved in _Anchitherium_. + +When we consider these facts, and the further circumstance that the +Hipparions, the remains of which have been collected in immense numbers, +were subject, as M. Gaudry and others have pointed out, to a great range +of variation, it appears to me impossible to resist the conclusion that +the types of the _Anchitherium_, of the _Hipparion_, and of the ancient +Horses constitute the lineage of the modern Horses, the _Hipparion_ being +the intermediate stage between the other two, and answering to B in my +former illustration. + +The process by which the _Anchitherium_ has been converted into _Equus_ +is one of specialisation, or of more and more complete deviation from +what might be called the average form of an ungulate mammal. In the +Horses, the reduction of some parts of the limbs, together with the +special modification of those which are left, is carried to a greater +extent than in any other hoofed mammals. The reduction is less and the +specialisation is less in the _Hipparion_, and still less in the +_Anchitherium_; but yet, as compared with other mammals, the reduction +and specialisation of parts in the _Anchitherium_ remain great. + +Is it not probable then, that, just as in the Miocene epoch, we find an +ancestral equine form less modified than _Equus_, so, if we go back to +the Eocene epoch, we shall find some quadruped related to the +_Anchitherium_, as _Hipparion_ is related to _Equus_, and consequently +departing less from the average form? + +I think that this desideratum is very nearly, if not quite, supplied by +_Plagiolophus_, remains of which occur abundantly in some parts of the +Upper and Middle Eocene formations. The patterns of the grinding-teeth of +_Plagiolophus_ are similar to those of _Anchitherium_, and their crowns +are as thinly covered with cement; but the grinders diminish in size +forwards, and the last lower molar has a large hind lobe, convex outwards +and concave inwards, as in _Palueotherium_. The ulna is complete and much +larger than in any of the _Equidoe_, while it is more slender than in +most of the true _Paloeotheria_; it is fixedly united, but not ankylosed, +with the radius. There are three toes in the fore limb, the outer ones +being slender, but less attenuated than in the _Equidoe_. The femur is +more like that of the _Paloeotheria_ than that of the horse, and has only +a small depression above its outer condyle in the place of the great +fossa which is so obvious in the _Equidoe_. The fibula is distinct, but +very slender, and its distal end is ankylosed with the tibia. There are +three toes on the hind foot having similar proportions to those on the +fore foot. The principal metacarpal and metatarsal bones are flatter than +they are in any of the _Equidoe_; and the metacarpal bones are longer +than the metatarsals, as in the _Paloeotheria_. + +In its general form, _Plagiolophus_ resembles a very small and slender +horse,[4] and is totally unlike the reluctant, pig-like creature depicted +in Cuvier's restoration of his _Paloeotherium minus_ in the "Ossemens +Fossiles." + +[Footnote 4: Such, at least, is the conclusion suggested by the +proportions of the skeleton figured by Cuvier and De Blainville; but +perhaps something between a Horse and an Agouti would be nearest the +mark.] + +It would be hazardous to say that _Plagiolophus_ is the exact radical +form of the Equine quadrupeds; but I do not think there can be any +reasonable doubt that the latter animals have resulted from the +modification of some quadruped similar to _Plagiolophus_. + +We have thus arrived at the Middle Eocene formation, and yet have traced +back the Horses only to a three-toed stock; but these three-toed forms, +no less than the Equine quadrupeds themselves, present rudiments of the +two other toes which appertain to what I have termed the "average" +quadruped. If the expectation raised by the splints of the Horses that, +in some ancestor of the Horses, these splints would be found to be +complete digits, has been verified, we are furnished with very strong +reasons for looking for a no less complete verification of the +expectation that the three-toed _Plagiolophus_-like "avus" of the horse +must have had a five-toed "atavus" at some earlier period. + +No such five-toed "atavus," however, has yet made its appearance among +the few middle and older Eocene _Mammalia_ which are known. + +Another series of closely affiliated forms, though the evidence they +afford is perhaps less complete than that of the Equine series, is +presented to us by the _Dichobune_ of the Eocene epoch, the +_Cainotherium_ of the Miocene, and the _Tragulidoe_, or so-called "Musk- +deer," of the present day. + +The _Tragulidoe_; have no incisors in the upper jaw, and only six +grinding-teeth on each side of each jaw; while the canine is moved up to +the outer incisor, and there is a diastema in the lower jaw. There are +four complete toes on the hind foot, but the middle metatarsals usually +become, sooner or later, ankylosed into a cannon bone. The navicular and +the cuboid unite, and the distal end of the fibula is ankylosed with the +tibia. + +In _Cainotherium_ and _Dichobune_ the upper incisors are fully developed. +There are seven grinders; the teeth form a continuous series without a +diastema. The metatarsals, the navicular and cuboid, and the distal end +of the fibula, remain free. In the _Cainotherium_, also, the second +metacarpal is developed, but is much shorter than the third, while the +fifth is absent or rudimentary. In this respect it resembles +_Anoplotherium secundarium_. This circumstance, and the peculiar pattern +of the upper molars in _Cainotherium_, lead me to hesitate in considering +it as the actual ancestor of the modern _Tragulidoe_. If _Dichobune_ has +a fore-toed fore foot (though I am inclined to suspect that it resembles +_Cainotherium_), it will be a better representative of the oldest forms +of the Traguline series; but _Dichobune_ occurs in the Middle Eocene, and +is, in fact, the oldest known artiodactyle mammal. Where, then, must we +look for its five-toed ancestor? + +If we follow down other lines of recent and tertiary _Ungulata_, the same +question presents itself. The Pigs are traceable back through the Miocene +epoch to the Upper Eocene, where they appear in the two well-marked forms +of _Hyopopotamus_ and _Choeropotamus_; but _Hyopotamus_ appears to have +had only two toes. + +Again, all the great groups of the Ruminants, the _Bovidoe, Antilopidoe, +Camelopardalidoe_, and _Cervidoe_, are represented in the Miocene epoch, +and so are the Camels. The Upper Eocene _Anoplotherium_, which is +intercalary between the Pigs and the _Tragulidoe_, has only two, or, at +most, three toes. Among the scanty mammals of the Lower Eocene formation +we have the perissodactyle _Ungulata_ represented by _Coryphodon, +Hyracotherium_, and _Pliolophus_. Suppose for a moment, for the sake of +following out the argument, that _Pliolophus_ represents the primary +stock of the Perissodactyles, and _Dichobune_ that of the Artiodactyles +(though I am far from saying that such is the case), then we find, in the +earliest fauna of the Eocene epoch to which our investigations carry us, +the two divisions of the _Ungulata_ completely differentiated, and no +trace of any common stock of both, or of five-toed predecessors to +either. With the case of the Horses before us, justifying a belief in the +production of new animal forms by modification of old ones, I see no +escape from the necessity of seeking for these ancestors of the +_Ungulata_ beyond the limits of the Tertiary formations. + +I could as soon admit special creation, at once, as suppose that the +Perissodactyles and Artiodactyles had no five-toed ancestors. And when we +consider how large a portion of the Tertiary period elapsed before +_Anchitherium_ was converted into _Equus_, it is difficult to escape the +conclusion that a large proportion of time anterior to the Tertiary +period must have been expended in converting the common stock of the +_Ungulata_ into Perissodactyles and Artiodactyles. + +The same moral is inculcated by the study of every other order of +Tertiary monodelphous _Mammalia_. Each of these orders is represented in +the Miocene epoch: the Eocene formation, as I have already said, contains +_Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora_, and _Cetacea_. +But the _Cheiroptera_ are extreme modifications of the _Insectivora_, +just as the _Cetacea_ are extreme modifications of the Carnivorous type; +and therefore it is to my mind incredible that monodelphous _Insectivora_ +and _Carnivora_ should not have been abundantly developed, along with +_Ungulata_, in the Mesozoic epoch. But if this be the case, how much +further back must we go to find the common stock of the monodelphous +_Mammalia_? As to the _Didelphia_, if we may trust the evidence which +seems to be afforded by their very scanty remains, a Hypsiprymnoid form +existed at the epoch of the Trias, contemporaneously with a Carnivorous +form. At the epoch of the Trias, therefore, the _Marsupialia_ must have +already existed long enough to have become differentiated into +carnivorous and herbivorous forms. But the _Monotremata_ are lower forms +than the _Didelphia_ which last are intercalary between the +_Ornithodelphia_ and the _Monodelphia_. To what point of the Palaeozoic +epoch, then, must we, upon any rational estimate, relegate the origin of +the _Monotremata?_ + +The investigation of the occurrence of the classes and of the orders of +the _Sauropsida_ in time points in exactly the same direction. If, as +there is great reason to believe, true Birds existed in the Triassic +epoch, the ornithoscelidous forms by which Reptiles passed into Birds +must have preceded them. In fact there is, even at present, considerable +ground for suspecting the existence of _Dinosauria_ in the Permian +formations; but, in that case, lizards must be of still earlier date. And +if the very small differences which are observable between the +_Crocodilia_ of the older Mesozoic formations and those of the present +day furnish any sort of approximation towards an estimate of the average +rate of change among the _Sauropsida_, it is almost appalling to reflect +how far back in Palaeozoic times we must go, before we can hope to arrive +at that common stock from which the _Crocodilia, Lacertilia, +Ornithoscelida_, and _Plesiosauria_, which had attained so great a +development in the Triassic epoch, must have been derived. + +The _Amphibia_ and _Pisces_ tell the same story. There is not a single +class of vertebrated animals which, when it first appears, is represented +by analogues of the lowest known members of the same class. Therefore, if +there is any truth in the doctrine of evolution, every class must be +vastly older than the first record of its appearance upon the surface of +the globe. But if considerations of this kind compel us to place the +origin of vertebrated animals at a period sufficiently distant from the +Upper Silurian, in which the first Elasmobranchs and Ganoids occur, to +allow of the evolution of such fishes as these from a Vertebrate as +simple as the _Amphioxus,_ I can only repeat that it is appalling to +speculate upon the extent to which that origin must have preceded the +epoch of the first recorded appearance of vertebrate life. + + +Such is the further commentary which I have to offer upon the statement +of the chief results of palaeontology which I formerly ventured to lay +before you. + +But the growth of knowledge in the interval makes me conscious of an +omission of considerable moment in that statement, inasmuch as it +contains no reference to the bearings of palaeontology upon the theory of +the distribution of life; nor takes note of the remarkable manner in +which the facts of distribution, in present and past times, accord with +the doctrine of evolution, especially in regard to land animals. + +That connection between palaeontology and geology and the present +distribution of terrestrial animals, which so strikingly impressed Mr. +Darwin, thirty years ago, as to lead him to speak of a "law of succession +of types," and of the wonderful relationship on the same continent +between the dead and the living, has recently received much elucidation +from the researches of Gaudry, of Rutimeyer, of Leidy, and of Alphonse +Milne-Edwards, taken in connection with the earlier labours of our +lamented colleague Falconer; and it has been instructively discussed in +the thoughtful and ingenious work of Mr. Andrew Murray "On the +Geographical Distribution of Mammals."[5] + +[Footnote 5: The paper "On the Form and Distribution of the Landtracts +during the Secondary and Tertiary Periods respectively; and on the Effect +upon Animal Life which great Changes in Geographical Configuration have +probably produced," by Mr. Searles V. Wood, jun., which was published in +the _Philosophical Magazine_, in 1862, was unknown to me when this +Address was written. It is well worthy of the most careful study.] + +I propose to lay before you, as briefly as I can, the ideas to which a +long consideration of the subject has given rise in my mind. + +If the doctrine of evolution is sound, one of its immediate consequences +clearly is, that the present distribution of life upon the globe is the +product of two factors, the one being the distribution which obtained in +the immediately preceding epoch, and the other the character and the +extent of the changes which have taken place in physical geography +between the one epoch and the other; or, to put the matter in another +way, the Fauna and Flora of any given area, in any given epoch, can +consist only of such forms of life as are directly descended from those +which constituted the Fauna and Flora of the same area in the immediately +preceding epoch, unless the physical geography (under which I include +climatal conditions) of the area has been so altered as to give rise to +immigration of living forms from some other area. + +The evolutionist, therefore, is bound to grapple with the following +problem whenever it is clearly put before him:--Here are the Faunae of the +same area during successive epochs. Show good cause for believing either +that these Faunae have been derived from one another by gradual +modification, or that the Faunae have reached the area in question by +migration from some area in which they have undergone their development. + +I propose to attempt to deal with this problem, so far as it is +exemplified by the distribution of the terrestrial _Vertebrata_, and I +shall endeavour to show you that it is capable of solution in a sense +entirely favourable to the doctrine of evolution. + +I have elsewhere[6] stated at length the reasons which lead me to +recognise four primary distributional provinces for the terrestrial +_Vertebrata_ in the present world, namely,--first, the _Novozelanian_, or +New-Zealand province; secondly, the _Australian_ province, including +Australia, Tasmania, and the Negrito Islands; thirdly, _Austro-Columbia_, +or South America _plus_ North America as far as Mexico; and fourthly, the +rest of the world, or _Arctogoea_, in which province America north of +Mexico constitutes one sub-province, Africa south of the Sahara a second, +Hindostan a third, and the remainder of the Old World a fourth. + +[Footnote 6: "On the Classification and Distribution of the +Alectoromorphoe;" _Proceedings of the Zoological Society_, 1868.] + +Now the truth which Mr. Darwin perceived and promulgated as "the law of +the succession of types" is, that, in all these provinces, the animals +found in Pliocene or later deposits are closely affined to those which +now inhabit the same provinces; and that, conversely, the forms +characteristic of other provinces are absent. North and South America, +perhaps, present one or two exceptions to the last rule, but they are +readily susceptible of explanation. Thus, in Australia, the later +Tertiary mammals are marsupials (possibly with the exception of the Dog +and a Rodent or two, as at present). In Austro-Columbia, the later +Tertiary fauna exhibits numerous and varied forms of Platyrrhine Apes, +Rodents, Cats, Dogs, Stags, _Edentata_, and Opossums; but, as at present, +no Catarrhine Apes, no Lemurs, no _Insectivora_, Oxen, Antelopes, +Rhinoceroses, nor _Didelphia_ other than Opossums. And in the widespread +Arctogaeal province, the Pliocene and later mammals belong to the same +groups as those which now exist in the province. The law of succession of +types, therefore, holds good for the present epoch as compared with its +predecessor. Does it equally well apply to the Pliocene fauna when we +compare it with that of the Miocene epoch? By great good fortune, an +extensive mammalian fauna of the latter epoch has now become known, in +four very distant portions of the Arctogaeal province which do not differ +greatly in latitude. Thus Falconer and Cautley have made known the fauna +of the sub-Himalayas and the Perim Islands; Gaudry that of Attica; many +observers that of Central Europe and France; and Leidy that of Nebraska, +on the eastern flank of the Rocky Mountains. The results are very +striking. The total Miocene fauna comprises many genera and species of +Catarrhine Apes, of Bats, of _Insectivora_; of Arctogaeal types of +_Rodentia_; of _Proboscidea_; of equine, rhinocerotic, and tapirine +quadrupeds; of cameline, bovine, antilopine, cervine, and traguline +Ruminants; of Pigs and Hippopotamuses; of _Viverridoe_ and _Hyoenidoe_ +among other _Carnivora_; with _Edentata_ allied to the Aretogaeal +_Oryeteropus_ and _Manis_, and not to the Austro-Columbian Edentates. The +only type present in the Miocene, but absent in the existing, fauna of +Eastern Arctogaea, is that of the _Didelphidoe_, which, however, remains +in North America. + +But it is very remarkable that while the Miocene fauna of the Arctogaeal +province, as a whole, is of the same character as the existing fauna of +the same province, as a whole, the component elements of the fauna were +differently associated. In the Miocene epoch, North America possessed +Elephants, Horses, Rhinoceroses, and a great number and variety of +Ruminants and Pigs, which are absent in the present indigenous fauna; +Europe had its Apes, Elephants, Rhinoceroses, Tapirs, Musk-deer, +Giraffes, Hyaenas, great Cats, Edentates, and Opossum-like Marsupials, +which have equally vanished from its present fauna; and in Northern +India, the African types of Hippopotamuses, Giraffes, and Elephants were +mixed up with what are now the Asiatic types of the latter, and with +Camels, and Semnopithecine and Pithecine Apes of no less distinctly +Asiatic forms. + +In fact the Miocene mammalian fauna of Europe and the Himalayan regions +contains, associated together, the types which are at present separately +located in the South-African and Indian sub-provinces of Arctogaea. Now +there is every reason to believe, on other grounds, that both Hindostan, +south of the Ganges, and Africa, south of the Sahara, were separated by a +wide sea from Europe and North Asia during the Middle and Upper Eocene +epochs. Hence it becomes highly probable that the well-known +similarities, and no less remarkable differences between the present +Faunae of India and South Africa have arisen in some such fashion as the +following. Some time during the Miocene epoch, possibly when the +Himalayan chain was elevated, the bottom of the nummulitic sea was +upheaved and converted into dry land, in the direction of a line +extending from Abyssinia to the mouth of the Ganges. By this means, the +Dekhan on the one hand, and South Africa on the other, became connected +with the Miocene dry land and with one another. The Miocene mammals +spread gradually over this intermediate dry land; and if the condition of +its eastern and western ends offered as wide contrasts as the valleys of +the Ganges and Arabia do now, many forms which made their way into Africa +must have been different from those which reached the Dekhan, while +others might pass into both these sub-provinces. + +That there was a continuity of dry land between Europe and North America +during the Miocene epoch, appears to me to be a necessary consequence of +the fact that many genera of terrestrial mammals, such as _Castor, +Hystrix, Elephas, Mastodon, Equus, Hipparion, Anchitherium, Rhinoceros, +Cervus, Amphicyon, Hyoenarctos_, and _Machairodus_, are common to the +Miocene formations of the two areas, and have as yet been found (except +perhaps _Anchitherium_) in no deposit of earlier age. Whether this +connection took place by the east, or by the west, or by both sides of +the Old World, there is at present no certain evidence, and the question +is immaterial to the present argument; but, as there are good grounds for +the belief that the Australian province and the Indian and South-African +sub-provinces were separated by sea from the rest of Arctogaea before the +Miocene epoch, so it has been rendered no less probable, by the +investigations of Mr. Carrick Moore and Professor Duncan, that Austro- +Columbia was separated by sea from North America during a large part of +the Miocene epoch. + +It is unfortunate that we have no knowledge of the Miocene mammalian +fauna of the Australian and Austro-Columbian provinces; but, seeing that +not a trace of a Platyrrhine Ape, of a Procyonine Carnivore, of a +characteristically South-American Rodent, of a Sloth, an Armadillo, or an +Ant-eater has yet been found in Miocene deposits of Arctogaea, I cannot +doubt that they already existed in the Miocene Austro-Columbian province. + +Nor is it less probable that the characteristic types of Australian +Mammalia were already developed in that region in Miocene times. + +But Austro-Columbia presents difficulties from which Australia is free; +_Cantelidoe_ and _Tapirdoe_ are now indigenous in South America as they +are in Arctogaea; and, among the Pliocene Austro-Columbian mammals, the +Arctogaeal genera _Equus, Mastodon,_ and _Machairodus_ are numbered. Are +these Postmiocene immigrants, or Praemiocene natives? + +Still more perplexing are the strange and interesting forms _Toxodon, +Macrauchenia, Typotherium_, and a new Anoplotherioid mammal +(_Homalodotherhon_) which Dr. Cunningham sent over to me some time ago +from Patagonia. I confess I am strongly inclined to surmise that these +last, at any rate, are remnants of the population of Austro-Columbia +before the Miocene epoch, and were not derived from Arctogaea by way of +the north and east. + +The fact that this immense fauna of Miocene Arctogaea is now fully and +richly represented only in India and in South Africa, while it is shrunk +and depauperised in North Asia, Europe, and North America, becomes at +once intelligible, if we suppose that India and South Africa had but a +scanty mammalian population before the Miocene immigration, while the +conditions were highly favourable to the new comers. It is to be supposed +that these new regions offered themselves to the Miocene Ungulates, as +South America and Australia offered themselves to the cattle, sheep, and +horses of modern colonists. But, after these great areas were thus +peopled, came the Glacial epoch, during which the excessive cold, to say +nothing of depression and ice-covering, must have almost depopulated all +the northern parts of Arctogaea, destroying all the higher mammalian +forms, except those which, like the Elephant and Rhinoceros, could adjust +their coats to the altered conditions. Even these must have been driven +away from the greater part of the area; only those Miocene mammals which +had passed into Hindostan and into South Africa would escape decimation +by such changes in the physical geography of Arctogaea. And when the +northern hemisphere passed into its present condition, these lost tribes +of the Miocene Fauna were hemmed by the Himalayas, the Sahara, the Red +Sea, and the Arabian deserts, within their present boundaries. + +Now, on the hypothesis of evolution, there is no sort of difficulty in +admitting that the differences between the Miocene forms of the mammalian +Fauna and those which exist at present are the results of gradual +modification; and, since such differences in distribution as obtain are +readily explained by the changes which have taken place in the physical +geography of the world since the Miocene epoch, it is clear that the +result of the comparison of the Miocene and present Faunae is distinctly +in favour of evolution. Indeed I may go further. I may say that the +hypothesis of evolution explains the facts of Miocene, Pliocene, and +Recent distribution, and that no other supposition even pretends to +account for them. It is, indeed, a conceivable supposition that every +species of Rhinoceros and every species of Hyaena, in the long succession +of forms between the Miocene and the present species, was separately +constructed out of dust, or out of nothing, by supernatural power; but +until I receive distinct evidence of the fact, I refuse to run the risk +of insulting any sane man by supposing that he seriously holds such a +notion. + +Let us now take a step further back in time, and inquire into the +relations between the Miocene Fauna and its predecessor of the Upper +Eocene formation. + +Here it is to be regretted that our materials for forming a judgment are +nothing to be compared in point of extent or variety with those which are +yielded by the Miocene strata. However, what we do know of this Upper +Eocene Fauna of Europe gives sufficient positive information to enable us +to draw some tolerably safe inferences. It has yielded representatives of +_Insectivora_, of _Cheiroptera_, of _Rodentia_, of _Carnivora_, of +artiodactyle and perissodactyle _Ungulata_, and of opossum-like +Marsupials. No Australian type of Marsupial has been discovered in the +Upper Eocene strata, nor any Edentate mammal. The genera (except perhaps +in the case of some of the _Insectivora, Cheiroptera_, and _Rodentia_) +are different from those of the Miocene epoch, but present a remarkable +general similarity to the Miocene and recent genera. In several cases, as +I have already shown, it has now been clearly made out that the relation +between the Eocene and Miocene forms is such that the Eocene form is the +less specialised; while its Miocene ally is more so, and the +specialisation reaches its maximum in the recent forms of the same type. + +So far as the Upper Eocene and the Miocene Mammalian Faunae are +comparable, their relations are such as in no way to oppose the +hypothesis that the older are the progenitors of the more recent forms, +while, in some cases, they distinctly favour that hypothesis. The period +in tine and the changes in physical geography represented by the +nummulitic deposits are undoubtedly very great, while the remains of +Middle Eocene and Older Eocene Mammals are comparatively few. The general +facies of the Middle Eocene Fauna, however, is quite that of the Upper. +The Older Eocene pre-nummulitic mammalian Fauna contains Bats, two genera +of _Carivora_, three genera of _Ungulata_ (probably all perissodactyle), +and a didelphid Marsupial; all these forms, except perhaps the Bat and +the Opossum, belong to genera which are not known to occur out of the +Lower Eocene formation. The _Coryphodon_ appears to have been allied to +the Miocene and later Tapirs, while _Pliolophus_, in its skull and +dentition, curiously partakes of both artiodactyle and perissodactyle +characters; the third trochanter upon its femur, and its three-toed hind +foot, however, appear definitely to fix its position in the latter +division. + +There is nothing, then, in what is known of the older Eocene mammals of +the Arctogaeal province to forbid the supposition that they stood in an +ancestral relation to those of the Calcaire Grossier and the Gypsum of +the Paris basin, and that our present fauna, therefore, is directly +derived from that which already existed in Arctogaea at the commencement +of the Tertiary period. But if we now cross the frontier between the +Cainozoic and the Mesozoic faunae, as they are preserved within the +Arctogaeal area, we meet with an astounding change, and what appears to be +a complete and unmistakable break in the line of biological continuity. + +Among the twelve or fourteen species of _Mammalia_ which are said to have +been found in the Purbecks, not one is a member of the orders +_Cheiroptera, Rodentia, Ungulata_, or _Carnivora_, which are so well +represented in the Tertiaries. No _Insectivora_ are certainly known, nor +any opossum-like Marsupials. Thus there is a vast negative difference +between the Cainozoic and the Mesozoic mammalian faunae of Europe. But +there is a still more important positive difference, inasmuch as all +these Mammalia appear to be Marsupials belonging to Australian groups, +and thus appertaining to a different distributional province from the +Eocene and Miocene marsupials, which are Austro-Columbian. So far as the +imperfect materials which exist enable a judgment to be formed, the same +law appears to have held good for all the earlier Mesozoic _Mammalia_. Of +the Stonesfield slate mammals, one, _Amphitherium_, has a definitely +Australian character; one, _Phascolotherium_, may be either Dasyurid or +Didelphine; of a third, _Stereognathus_, nothing can at present be said. +The two mammals of the Trias, also, appear to belong to Australian +groups. + +Every one is aware of the many curious points of resemblance between the +marine fauna of the European Mesozoic rocks and that which now exists in +Australia. But if there was this Australian facies about both the +terrestrial and the marine faunae of Mesozoic Europe, and if there is this +unaccountable and immense break between the fauna of Mesozoic and that of +Tertiary Europe, is it not a very obvious suggestion that, in the +Mesozoic epoch, the Australian province included Europe, and that the +Arctogaeal province was contained within other limits? The Arctogaeal +province is at present enormous, while the Australian is relatively +small. Why should not these proportions have been different during the +Mesozoic epoch? + +Thus I am led to think that by far the simplest and most rational mode of +accounting for the great change which took place in the living +inhabitants of the European area at the end of the Mesozoic epoch, is the +supposition that it arose from a vast alteration of the physical +geography of the globe; whereby an area long tenanted by Cainozoic forms +was brought into such relations with the European area that migration +from the one to the other became possible, and took place on a great +scale. + +This supposition relieves us, at once, from the difficulty in which we +were left, some time ago, by the arguments which I used to demonstrate +the necessity of the existence of all the great types of the Eocene epoch +in some antecedent period. + +It is this Mesozoic continent (which may well have lain in the +neighbourhood of what are now the shores of the North Pacific Ocean) +which I suppose to have been occupied by the Mesozoic _Monodelphia_; and +it is in this region that I conceive they must have gone through the long +series of changes by which they were specialised into the forms which we +refer to different orders. I think it very probable that what is now +South America may have received the characteristic elements of its +mammalian fauna during the Mesozoic epoch; and there can be little doubt +that the general nature of the change which took place at the end of the +Mesozoic epoch in Europe was the upheaval of the eastern and northern +regions of the Mesozoic sea-bottom into a westward extension of the +Mesozoic continent, over which the mammalian fauna, by which it was +already peopled, gradually spread. This invasion of the land was prefaced +by a previous invasion of the Cretaceous sea by modern forms of mollusca +and fish. + +It is easy to imagine how an analogous change might come about in the +existing world. There is, at present, a great difference between the +fauna of the Polynesian Islands and that of the west coast of America. +The animals which are leaving their spoils in the deposits now forming in +these localities are widely different. Hence, if a gradual shifting of +the deep sea, which at present bars migration between the easternmost of +these islands and America, took place to the westward, while the American +side of the sea-bottom was gradually upheaved, the palaeontologist of the +future would find, over the Pacific area, exactly such a change as I am +supposing to have occurred in the North-Atlantic area at the close of the +Mesozoic period. An Australian fauna would be found underlying an +American fauna, and the transition from the one to the other would be as +abrupt as that between the Chalk and lower Tertiaries; and as the +drainage-area of the newly formed extension of the American continent +gave rise to rivers and lakes, the mammals mired in their mud would +differ from those of like deposits on the Australian side, just as the +Eocene mammals differ from those of the Purbecks. + +How do similar reasonings apply to the other great change of life--that +which took place at the end of the Palaeozoic period? + +In the Triassic epoch, the distribution of the dry land and of +terrestrial vertebrate life appears to have been, generally, similar to +that which existed in the Mesozoic epoch; so that the Triassic continents +and their faunae seem to be related to the Mesozoic lands and their faunae, +just as those of the Miocene epoch are related to those of the present +day. In fact, as I have recently endeavoured to prove to the Society, +there was an Arctogaeal continent and an Arctogaeal province of +distribution in Triassic times as there is now; and the _Sauropsida_ and +_Marsupialia_ which constituted that fauna were, I doubt not, the +progenitors of the _Sauropsida_ and _Marsupialia_ of the whole Mesozoic +epoch. + +Looking at the present terrestrial fauna of Australia, it appears to me +to be very probable that it is essentially a remnant of the fauna of the +Triassic, or even of an earlier, age[7] in which case Australia must at +that time have been in continuity with the Arctogaeal continent. + +[Footnote 7: Since this Address was read, Mr. Krefft has sent us news of +the discovery in Australia of a freshwater fish of strangely Palaeozoic +aspect, and apparently a Ganoid intermediate between _Dipterus_ and +_Lepidosiren_. [The now well-known _Ceratodus_. 1894.]] + +But now comes the further inquiry, Where was the highly differentiated +Sauropsidan fauna of the Trias in Palaeozoic times? The supposition that +the Dinosaurian, Crocodilian, Dicynodontian, and to Plesiosaurian types +were suddenly created at the end of the Permian epoch may be dismissed, +without further consideration, as a monstrous and unwarranted assumption. +The supposition that all these types were rapidly differentiated out of +_Lacertilia_ in the time represented by the passage from the Palaeozoic to +the Mesozoic formation, appears to me to be hardly more credible, to say +nothing of the indications of the existence of Dinosaurian forms in the +Permian rocks which have already been obtained. + +For my part, I entertain no sort of doubt that the Reptiles, Birds, and +Mammals of the Trias are the direct descendants of Reptiles, Birds, and +Mammals which existed in the latter part of the Palaeozoic epoch, but not +in any area of the present dry land which has yet been explored by the +geologist. + +This may seem a bold assumption, but it will not appear unwarrantable to +those who reflect upon the very small extent of the earth's surface which +has hitherto exhibited the remains of the great Mammalian fauna of the +Eocene times. In this respect, the Permian land Vertebrate fauna appears +to me to be related to the Triassic much as the Eocene is to the Miocene. +Terrestrial reptiles have been found in Permian rocks only in three +localities; in some spots of France, and recently of England, and over a +more extensive area in Germany. Who can suppose that the few fossils yet +found in these regions give any sufficient representation of the Permian +fauna? + +It may be said that the Carboniferous formations demonstrate the +existence of a vast extent of dry land in the present dry-land area, and +that the supposed terrestrial Palaeozoic Vertebrate Fauna ought to have +left its remains in the Coal-measures, especially as there is now reason +to believe that much of the coal was formed by the accumulation of spores +and sporangia on dry land. But if we consider the matter more closely, I +think that this apparent objection loses its force. It is clear that, +during the Carboniferous epoch, the vast area of land which is now +covered by Coal-measures must have been undergoing a gradual depression. +The dry land thus depressed must, therefore, have existed, as such, +before the Carboniferous epoch--in other words, in Devonian times--and +its terrestrial population may never have been other than such as existed +during the Devonian, or some previous epoch, although much higher forms +may have been developed elsewhere. + +Again, let me say that I am making no gratuitous assumption of +inconceivable changes. It is clear that the enormous area of Polynesia +is, on the whole, an area over which depression has taken place to an +immense extent; consequently a great continent, or assemblage of +subcontinental masses of land must have existed at some former time, and +that at a recent period, geologically speaking, in the area of the +Pacific. But if that continent had contained Mammals, some of them must +have remained to tell the tale; and as it is well known that these +islands have no indigenous _Mammalia_, it is safe to assume that none +existed. Thus, midway between Australia and South America, each of which +possesses an abundant and diversified mammalian fauna, a mass of land, +which may have been as large as both put together, must have existed +without a mammalian inhabitant. Suppose that the shores of this great +land were fringed, as those of tropical Australia are now, with belts of +mangroves, which would extend landwards on the one side, and be buried +beneath littoral deposits on the other side, as depression went on; and +great beds of mangrove lignite might accumulate over the sinking land. +Let upheaval of the whole now take place, in such a manner as to bring +the emerging land into continuity with the South-American or Australian +continent, and, in course of time, it would be peopled by an extension of +the fauna of one of these two regions--just as I imagine the European +Permian dry land to have been peopled. + +I see nothing whatever against the supposition that distributional +provinces of terrestrial life existed in the Devonian epoch, inasmuch as +M. Barrande has proved that they existed much earlier. I am aware of no +reason for doubting that, as regards the grades of terrestrial life +contained in them, one of these may have been related to another as New +Zealand is to Australia, or as Australia is to India, at the present day. +Analogy seems to me to be rather in favour of, than against, the +supposition that while only Ganoid fishes inhabited the fresh waters of +our Devonian land, _Amphibia_ and _Reptilia_, or even higher forms, may +have existed, though we have not yet found them. The earliest +Carboniferous _Amphibia_ now known, such as _Anthracosaurus_, are so +highly specialised that I can by no means conceive that they have been +developed out of piscine forms in the interval between the Devonian and +the Carboniferous periods, considerable as that is. And I take refuge in +one of two alternatives: either they existed in our own area during the +Devonian epoch and we have simply not yet found them; or they formed part +of the population of some other distributional province of that day, and +only entered our area by migration at the end of the Devonian epoch. +Whether _Reptilia_ and _Mammalia_ existed along with them is to me, at +present, a perfectly open question, which is just as likely to receive an +affirmative as a negative answer from future inquirers. + +Let me now gather together the threads of my argumentation into the form +of a connected hypothetical view of the manner in which the distribution +of living and extinct animals has been brought about. + +I conceive that distinct provinces of the distribution of terrestrial +life have existed since the earliest period at which that life is +recorded, and possibly much earlier; and I suppose, with Mr. Darwin, that +the progress of modification of terrestrial forms is more rapid in areas +of elevation than in areas of depression. I take it to be certain that +Labyrinthodont _Amphibia_ existed in the distributional province which +included the dry land depressed during the Carboniferous epoch; and I +conceive that, in some other distributional provinces of that day, which +remained in the condition of stationary or of increasing dry land, the +various types of the terrestrial _Sauropsida_ and of the _Mammalia_ were +gradually developing. + +The Permian epoch marks the commencement of a new movement of upheaval in +our area, which dry land existed in North America, Europe, Asia, and +Africa, as it does now. Into this great new continental area the Mammals, +Birds, and Reptiles developed during the Palaeozoic epoch spread, and +formed the great Triassic Arctogaeal province. But, at the end of the +Triassic period, the movement of depression recommenced in our area, +though it was doubtless balanced by elevation elsewhere; modification and +development, checked in the one province, went on in that "elsewhere"; +and the chief forms of Mammals, Birds and Reptiles, as we know them, were +evolved and peopled the Mesozoic continent. I conceive Australia to have +become separated from the continent as early as the end of the Triassic +epoch, or not much later. The Mesozoic continent must, I conceive, have +lain to the east, about the shores of the North Pacific and Indian +Oceans; and I am inclined to believe that it continued along the eastern +side of the Pacific area to what is now the province of Austro-Columbia, +the characteristic fauna of which is probably a remnant of the population +of the latter part of this period. + +Towards the latter part of the Mesozoic period the movement of upheaval +around the shores of the Atlantic once more recommenced, and was very +probably accompanied by a depression around those of the Pacific. The +Vertebrate fauna elaborated in the Mesozoic continent moved westward and +took possession of the new lands, which gradually increased in extent up +to, and in some directions after, the Miocene epoch. + +It is in favour of this hypothesis, I think, that it is consistent with +the persistence of a general uniformity in the positions of the great +masses of land and water. From the Devonian period, or earlier, to the +present day, the four great oceans, Atlantic, Pacific, Arctic, and +Antarctic, may have occupied their present positions, and only their +coasts and channels of communication have undergone an incessant +alteration. And, finally, the hypothesis I have put before you requires +no supposition that the rate of change in organic life has been either +greater or less in ancient times than it is now; nor any assumption, +either physical or biological, which has not its justification in +analogous phenomena of existing nature. + +I have now only to discharge the last duty of my office, which is to +thank you, not only for the patient attention with which you have +listened to me so long to-day, but also for the uniform kindness with +which, for the past two years, you have rendered my endeavours to perform +the important, and often laborious, functions of your President a +pleasure instead of a burden. + + + + + +End of the Project Gutenberg EBook of Discourses, by Thomas H. 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Huxley + +Release Date: November 12, 2003 [EBook #10060] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK DISCOURSES *** + + + + +Produced by Imran Ghory, Stan Goodman, +Richard Prairie and PG Distributed Proofreaders + + + + + DISCOURSES: + + BIOLOGICAL & GEOLOGICAL + + ESSAYS + + BY + + THOMAS H. HUXLEY + + 1894 + + + +PREFACE + + +The contents of the present volume, with three exceptions, are either +popular lectures, or addresses delivered to scientific bodies with which +I have been officially connected. I am not sure which gave me the more +trouble. For I have not been one of those fortunate persons who are able +to regard a popular lecture as a mere _hors d'oeuvre_, unworthy of being +ranked among the serious efforts of a philosopher; and who keep their +fame as scientific hierophants unsullied by attempts--at least of the +successful sort--to be understanded of the people. + +On the contrary, I found that the task of putting the truths learned in +the field, the laboratory and the museum, into language which, without +bating a jot of scientific accuracy shall be generally intelligible, +taxed such scientific and literary faculty as I possessed to the +uttermost; indeed my experience has furnished me with no better +corrective of the tendency to scholastic pedantry which besets all those +who are absorbed in pursuits remote from the common ways of men, and +become habituated to think and speak in the technical dialect of their +own little world, as if there were no other. + +If the popular lecture thus, as I believe, finds one moiety of its +justification in the self-discipline of the lecturer, it surely finds the +other half in its effect on the auditory. For though various sadly +comical experiences of the results of my own efforts have led me to +entertain a very moderate estimate of the purely intellectual value of +lectures; though I venture to doubt if more than one in ten of an average +audience carries away an accurate notion of what the speaker has been +driving at; yet is that not equally true of the oratory of the hustings, +of the House of Commons, and even of the pulpit? + +Yet the children of this world are wise in their generation; and both the +politician and the priest are justified by results. The living voice has +an influence over human action altogether independent of the intellectual +worth of that which it utters. Many years ago, I was a guest at a great +City dinner. A famous orator, endowed with a voice of rare flexibility +and power; a born actor, ranging with ease through every part, from +refined comedy to tragic unction, was called upon to reply to a toast. +The orator was a very busy man, a charming conversationalist and by no +means despised a good dinner; and, I imagine, rose without having given a +thought to what he was going to say. The rhythmic roll of sound was +admirable, the gestures perfect, the earnestness impressive; nothing was +lacking save sense and, occasionally, grammar. When the speaker sat down +the applause was terrific and one of my neighbours was especially +enthusiastic. So when he had quieted down, I asked him what the orator +had said. And he could not tell me. + +That sagacious person John Wesley, is reported to have replied to some +one who questioned the propriety of his adaptation of sacred words to +extremely secular airs, that he did not see why the Devil should be left +in possession of all the best tunes. And I do not see why science should +not turn to account the peculiarities of human nature thus exploited by +other agencies: all the more because science, by the nature of its being, +cannot desire to stir the passions, or profit by the weaknesses, of human +nature. The most zealous of popular lecturers can aim at nothing more +than the awakening of a sympathy for abstract truth, in those who do not +really follow his arguments; and of a desire to know more and better in +the few who do. + +At the same time it must be admitted that the popularization of science, +whether by lecture or essay, has its drawbacks. Success in this +department has its perils for those who succeed. The "people who fail" +take their revenge, as we have recently had occasion to observe, by +ignoring all the rest of a man's work and glibly labelling him a more +popularizer. If the falsehood were not too glaring, they would say the +same of Faraday and Helmholtz and Kelvin. + +On the other hand, of the affliction caused by persons who think that +what they have picked up from popular exposition qualifies them for +discussing the great problems of science, it may be said, as the Radical +toast said of the power of the Crown in bygone days, that it "has +increased, is increasing, and ought to be diminished." The oddities of +"English as she is spoke" might be abundantly paralleled by those of +"Science as she is misunderstood" in the sermon, the novel, and the +leading article; and a collection of the grotesque travesties of +scientific conceptions, in the shape of essays on such trifles as "the +Nature of Life" and the "Origin of All Things," which reach me, from time +to time, might well be bound up with them. + + +The tenth essay in this volume unfortunately brought me, I will not say +into collision, but into a position of critical remonstrance with regard +to some charges of physical heterodoxy, brought by my distinguished +friend Lord Kelvin, against British Geology. As President of the +Geological Society of London at that time (1869), I thought I might +venture to plead that we were not such heretics as we seemed to be; and +that, even if we were, recantation would not affect the question of +evolution. + +I am glad to see that Lord Kelvin has just reprinted his reply to my +plea,[1] and I refer the reader to it. I shall not presume to question +anything, that on such ripe consideration, Lord Kelvin has to say upon +the physical problems involved. But I may remark that no one can have +asserted more strongly than I have done, the necessity of looking to +physics and mathematics, for help in regard to the earliest history of +the globe. (See pp. 108 and 109 of this volume.) + +[Footnote 1: _Popular Lectures and Addresses._ II. Macmillan and Co. +1894.] + +And I take the opportunity of repeating the opinion, that, whether what +we call geological time has the lower limit assigned to it by Lord +Kelvin, or the higher assumed by other philosophers; whether the germs of +all living things have originated in the globe itself, or whether they +have been imported on, or in, meteorites from without, the problem of the +origin of those successive Faunae and Florae of the earth, the existence of +which is fully demonstrated by paleontology remains exactly where it was. + +For I think it will be admitted, that the germs brought to us by +meteorites, if any, were not ova of elephants, nor of crocodiles; not +cocoa-nuts nor acorns; not even eggs of shell-fish and corals; but only +those of the lowest forms of animal and vegetable life. Therefore, since +it is proved that, from a very remote epoch of geological time, the earth +has been peopled by a continual succession of the higher forms of animals +and plants, these either must have been created, or they have arisen by +evolution. And in respect of certain groups of animals, the well- +established facts of paleontology leave no rational doubt that they arose +by the latter method. + +In the second place, there are no data whatever, which justify the +biologist in assigning any, even approximately definite, period of time, +either long or short, to the evolution of one species from another by the +process of variation and selection. In the ninth of the following essays, +I have taken pains to prove that the change of animals has gone on at +very different rates in different groups of living beings; that some +types have persisted with little change from the paleozoic epoch till +now, while others have changed rapidly within the limits of an epoch. In +1862 (see below p. 303, 304) in 1863 (vol. II., p. 461) and again in 1864 +(ibid., p. 89-91) I argued, not as a matter of speculation, but, from +paleontological facts, the bearing of which I believe, up to that time, +had not been shown, that any adequate hypothesis of the causes of +evolution must be consistent with progression, stationariness and +retrogression, of the same type at different epochs; of different types +in the same epoch; and that Darwin's hypothesis fulfilled these +conditions. + +According to that hypothesis, two factors are at work, variation and +selection. Next to nothing is known of the causes of the former process; +nothing whatever of the time required for the production of a certain +amount of deviation from the existing type. And, as respects selection, +which operates by extinguishing all but a small minority of variations, +we have not the slightest means of estimating the rapidity with which it +does its work. All that we are justified in saying is that the rate at +which it takes place may vary almost indefinitely. If the famous paint- +root of Florida, which kills white pigs but not black ones, were abundant +and certain in its action, black pigs might be substituted for white in +the course of two or three years. If, on the other hand, it was rare and +uncertain in action, the white pigs might linger on for centuries. + +T.H. HUXLEY. + +HODESLEA, EASTBOURNE, + +_April, 1894._ + + + +CONTENTS + + +I + +ON A PIECE OF CHALK [1868] +(A Lecture delivered to the working men of Norwich during the meeting of +the British Association.) + + +II + +THE PROBLEMS OF THE DEEP SEA [1878] + + +III + +ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. "CHALLENGER" [1875] + + +IV + +YEAST [1871] + + +V + +ON THE FORMATION OF COAL [1870] +(A Lecture delivered at the Philosophical Institute, Bradford.) + + +VI + +ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS +[1876] +(A Friday evening Lecture delivered at the Royal Institution.) + + +VII + +A LOBSTER; OR, THE STUDY OF ZOOLOGY [1861] +(A Lecture delivered at the South Kensington Museum.) + + +VIII + +BIOGENESIS AND ABIOGENESIS [1870] +(The Presidential Address to the Meeting of the British Association for +the Advancement of Science at Liverpool.) + + +IX + +GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE [1862] +(Address to the Geological Society on behalf of the President by one of +the Secretaries.) + + +X + +GEOLOGICAL REFORM [1869] +(Presidential Address to the Geological Society.) + + +XI + +PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION [1870] +(Presidential Address to the Geological Society.) + + + +I + + +ON A PIECE OF CHALK + +[1868] + +If a well were sunk at our feet in the midst of the city of Norwich, the +diggers would very soon find themselves at work in that white substance +almost too soft to be called rock, with which we are all familiar as +"chalk." + +Not only here, but over the whole county of Norfolk, the well-sinker +might carry his shaft down many hundred feet without coming to the end of +the chalk; and, on the sea-coast, where the waves have pared away the +face of the land which breasts them, the scarped faces of the high cliffs +are often wholly formed of the same material. Northward, the chalk may be +followed as far as Yorkshire; on the south coast it appears abruptly in +the picturesque western bays of Dorset, and breaks into the Needles of +the Isle of Wight; while on the shores of Kent it supplies that long line +of white cliffs to which England owes her name of Albion. + +Were the thin soil which covers it all washed away, a curved band of +white chalk, here broader, and there narrower, might be followed +diagonally across England from Lulworth in Dorset, to Flamborough Head in +Yorkshire--a distance of over 280 miles as the crow flies. From this band +to the North Sea, on the east, and the Channel, on the south, the chalk +is largely hidden by other deposits; but, except in the Weald of Kent and +Sussex, it enters into the very foundation of all the south-eastern +counties. + +Attaining, as it does in some places, a thickness of more than a thousand +feet, the English chalk must be admitted to be a mass of considerable +magnitude. Nevertheless, it covers but an insignificant portion of the +whole area occupied by the chalk formation of the globe, much of which +has the same general characters as ours, and is found in detached +patches, some less, and others more extensive, than the English. Chalk +occurs in north-west Ireland; it stretches over a large part of France,-- +the chalk which underlies Paris being, in fact, a continuation of that of +the London basin; it runs through Denmark and Central Europe, and extends +southward to North Africa; while eastward, it appears in the Crimea and +in Syria, and may be traced as far as the shores of the Sea of Aral, in +Central Asia. If all the points at which true chalk occurs were +circumscribed, they would lie within an irregular oval about 3,000 miles +in long diameter--the area of which would be as great as that of Europe, +and would many times exceed that of the largest existing inland sea--the +Mediterranean. + +Thus the chalk is no unimportant element in the masonry of the earth's +crust, and it impresses a peculiar stamp, varying with the conditions to +which it is exposed, on the scenery of the districts in which it occurs. +The undulating downs and rounded coombs, covered with sweet-grassed turf, +of our inland chalk country, have a peacefully domestic and mutton- +suggesting prettiness, but can hardly be called either grand or +beautiful. But on our southern coasts, the wall-sided cliffs, many +hundred feet high, with vast needles and pinnacles standing out in the +sea, sharp and solitary enough to serve as perches for the wary +cormorant, confer a wonderful beauty and grandeur upon the chalk +headlands. And, in the East, chalk has its share in the formation of some +of the most venerable of mountain ranges, such as the Lebanon. + +What is this wide-spread component of the surface of the earth? and +whence did it come? + + +You may think this no very hopeful inquiry. You may not unnaturally +suppose that the attempt to solve such problems as these can lead to no +result, save that of entangling the inquirer in vague speculations, +incapable of refutation and of verification. If such were really the +case, I should have selected some other subject than a "piece of chalk" +for my discourse. But, in truth, after much deliberation, I have been +unable to think of any topic which would so well enable me to lead you to +see how solid is the foundation upon which some of the most startling +conclusions of physical science rest. + +A great chapter of the history of the world is written in the chalk. Few +passages in the history of man can be supported by such an overwhelming +mass of direct and indirect evidence as that which testifies to the truth +of the fragment of the history of the globe, which I hope to enable you +to read, with your own eyes, to-night. Let me add, that few chapters of +human history have a more profound significance for ourselves. I weigh my +words well when I assert, that the man who should know the true history +of the bit of chalk which every carpenter carries about in his breeches- +pocket, though ignorant of all other history, is likely, if he will think +his knowledge out to its ultimate results, to have a truer, and therefore +a better, conception of this wonderful universe, and of man's relation to +it, than the most learned student who is deep-read in the records of +humanity and ignorant of those of Nature. + +The language of the chalk is not hard to learn, not nearly so hard as +Latin, if you only want to get at the broad features of the story it has +to tell; and I propose that we now set to work to spell that story out +together. + +We all know that if we "burn" chalk the result is quicklime. Chalk, in +fact, is a compound of carbonic acid gas, and lime, and when you make it +very hot the carbonic acid flies away and the lime is left. By this +method of procedure we see the lime, but we do not see the carbonic acid. +If, on the other hand, you were to powder a little chalk and drop it into +a good deal of strong vinegar, there would be a great bubbling and +fizzing, and, finally, a clear liquid, in which no sign of chalk would +appear. Here you see the carbonic acid in the bubbles; the lime, +dissolved in the vinegar, vanishes from sight. There are a great many +other ways of showing that chalk is essentially nothing but carbonic acid +and quicklime. Chemists enunciate the result of all the experiments which +prove this, by stating that chalk is almost wholly composed of "carbonate +of lime." + +It is desirable for us to start from the knowledge of this fact, though +it may not seem to help us very far towards what we seek. For carbonate +of lime is a widely-spread substance, and is met with under very various +conditions. All sorts of limestones are composed of more or less pure +carbonate of lime. The crust which is often deposited by waters which +have drained through limestone rocks, in the form of what are called +stalagmites and stalactites, is carbonate of lime. Or, to take a more +familiar example, the fur on the inside of a tea-kettle is carbonate of +lime; and, for anything chemistry tells us to the contrary, the chalk +might be a kind of gigantic fur upon the bottom of the earth-kettle, +which is kept pretty hot below. + +Let us try another method of making the chalk tell us its own history. To +the unassisted eye chalk looks simply like a very loose and open kind of +stone. But it is possible to grind a slice of chalk down so thin that you +can see through it--until it is thin enough, in fact, to be examined with +any magnifying power that may be thought desirable. A thin slice of the +fur of a kettle might be made in the same way. If it were examined +microscopically, it would show itself to be a more or less distinctly +laminated mineral substance, and nothing more. + +But the slice of chalk presents a totally different appearance when +placed under the microscope. The general mass of it is made up of very +minute granules; but, imbedded in this matrix, are innumerable bodies, +some smaller and some larger, but, on a rough average, not more than a +hundredth of an inch in diameter, having a well-defined shape and +structure. A cubic inch of some specimens of chalk may contain hundreds +of thousands of these bodies, compacted together with incalculable +millions of the granules. + +The examination of a transparent slice gives a good notion of the manner +in which the components of the chalk are arranged, and of their relative +proportions. But, by rubbing up some chalk with a brush in water and then +pouring off the milky fluid, so as to obtain sediments of different +degrees of fineness, the granules and the minute rounded bodies may be +pretty well separated from one another, and submitted to microscopic +examination, either as opaque or as transparent objects. By combining the +views obtained in these various methods, each of the rounded bodies may +be proved to be a beautifully-constructed calcareous fabric, made up of a +number of chambers, communicating freely with one another. The chambered +bodies are of various forms. One of the commonest is something like a +badly-grown raspberry, being formed of a number of nearly globular +chambers of different sizes congregated together. It is called +_Globigerina_, and some specimens of chalk consist of little else than +_Globigerinoe_ and granules. Let us fix our attention upon the +_Globigerina_. It is the spoor of the game we are tracking. If we can +learn what it is and what are the conditions of its existence, we shall +see our way to the origin and past history of the chalk. + +A suggestion which may naturally enough present itself is, that these +curious bodies are the result of some process of aggregation which has +taken place in the carbonate of lime; that, just as in winter, the rime +on our windows simulates the most delicate and elegantly arborescent +foliage--proving that the mere mineral water may, under certain +conditions, assume the outward form of organic bodies--so this mineral +substance, carbonate of lime, hidden away in the bowels of the earth, has +taken the shape of these chambered bodies. I am not raising a merely +fanciful and unreal objection. Very learned men, in former days, have +even entertained the notion that all the formed things found in rocks are +of this nature; and if no such conception is at present held to be +admissible, it is because long and varied experience has now shown that +mineral matter never does assume the form and structure we find in +fossils. If any one were to try to persuade you that an oyster-shell +(which is also chiefly composed of carbonate of lime) had crystallized +out of sea-water, I suppose you would laugh at the absurdity. Your +laughter would be justified by the fact that all experience tends to show +that oyster-shells are formed by the agency of oysters, and in no other +way. And if there were no better reasons, we should be justified, on like +grounds, in believing that _Globigerina_ is not the product of anything +but vital activity. + +Happily, however, better evidence in proof of the organic nature of the +_Globigerinoe_ than that of analogy is forthcoming. It so happens that +calcareous skeletons, exactly similar to the _Globigerinoe_ of the chalk, +are being formed, at the present moment, by minute living creatures, +which flourish in multitudes, literally more numerous than the sands of +the sea-shore, over a large extent of that part of the earth's surface +which is covered by the ocean. + +The history of the discovery of these living _Globigerinoe_, and of the +part which they play in rock building, is singular enough. It is a +discovery which, like others of no less scientific importance, has +arisen, incidentally, out of work devoted to very different and +exceedingly practical interests. When men first took to the sea, they +speedily learned to look out for shoals and rocks; and the more the +burthen of their ships increased, the more imperatively necessary it +became for sailors to ascertain with precision the depth of the waters +they traversed. Out of this necessity grew the use of the lead and +sounding line; and, ultimately, marine-surveying, which is the recording +of the form of coasts and of the depth of the sea, as ascertained by the +sounding-lead, upon charts. + +At the same time, it became desirable to ascertain and to indicate the +nature of the sea-bottom, since this circumstance greatly affects its +goodness as holding ground for anchors. Some ingenious tar, whose name +deserves a better fate than the oblivion into which it has fallen, +attained this object by "arming" the bottom of the lead with a lump of +grease, to which more or less of the sand or mud, or broken shells, as +the case might be, adhered, and was brought to the surface. But, however +well adapted such an apparatus might be for rough nautical purposes, +scientific accuracy could not be expected from the armed lead, and to +remedy its defects (especially when applied to sounding in great depths) +Lieut. Brooke, of the American Navy, some years ago invented a most +ingenious machine, by which a considerable portion of the superficial +layer of the sea-bottom can be scooped out and brought up from any depth +to which the lead descends. In 1853, Lieut. Brooke obtained mud from the +bottom of the North Atlantic, between Newfoundland and the Azores, at a +depth of more than 10,000 feet, or two miles, by the help of this +sounding apparatus. The specimens were sent for examination to Ehrenberg +of Berlin, and to Bailey of West Point, and those able microscopists +found that this deep-sea mud was almost entirely composed of the +skeletons of living organisms--the greater proportion of these being just +like the _Globigerinoe_ already known to occur in the chalk. + +Thus far, the work had been carried on simply in the interests of +science, but Lieut. Brooke's method of sounding acquired a high +commercial value, when the enterprise of laying down the telegraph-cable +between this country and the United States was undertaken. For it became +a matter of immense importance to know, not only the depth of the sea +over the whole line along which the cable was to be laid, but the exact +nature of the bottom, so as to guard against chances of cutting or +fraying the strands of that costly rope. The Admiralty consequently +ordered Captain Dayman, an old friend and shipmate of mine, to ascertain +the depth over the whole line of the cable, and to bring back specimens +of the bottom. In former days, such a command as this might have sounded +very much like one of the impossible things which the young Prince in the +Fairy Tales is ordered to do before he can obtain the hand of the +Princess. However, in the months of June and July, 1857, my friend +performed the task assigned to him with great expedition and precision, +without, so far as I know, having met with any reward of that kind. The +specimens or Atlantic mud which he procured were sent to me to be +examined and reported upon.[1] + +[Footnote 1: See Appendix to Captain Dayman's _Deep-sea Soundings in the +North Atlantic Ocean between Ireland and Newfoundland, made in H.M.S. +"Cyclops_." Published by order of the Lords Commissioners of the +Admiralty, 1858. They have since formed the subject of an elaborate +Memoir by Messrs. Parker and Jones, published in the _Philosophical +Transactions_ for 1865.] + +The result of all these operations is, that we know the contours and the +nature of the surface-soil covered by the North Atlantic for a distance +of 1,700 miles from east to west, as well as we know that of any part of +the dry land. It is a prodigious plain--one of the widest and most even +plains in the world. If the sea were drained off, you might drive a +waggon all the way from Valentia, on the west coast of Ireland, to +Trinity Bay, in Newfoundland. And, except upon one sharp incline about +200 miles from Valentia, I am not quite sure that it would even be +necessary to put the skid on, so gentle are the ascents and descents upon +that long route. From Valentia the road would lie down-hill for about 200 +miles to the point at which the bottom is now covered by 1,700 fathoms of +sea-water. Then would come the central plain, more than a thousand miles +wide, the inequalities of the surface of which would be hardly +perceptible, though the depth of water upon it now varies from 10,000 to +15,000 feet; and there are places in which Mont Blanc might be sunk +without showing its peak above water. Beyond this, the ascent on the +American side commences, and gradually leads, for about 300 miles, to the +Newfoundland shore. + +Almost the whole of the bottom of this central plain (which extends for +many hundred miles in a north and south direction) is covered by a fine +mud, which, when brought to the surface, dries into a greyish white +friable substance. You can write with this on a blackboard, if you are so +inclined; and, to the eye, it is quite like very soft, grayish chalk. +Examined chemically, it proves to be composed almost wholly of carbonate +of lime; and if you make a section of it, in the same way as that of the +piece of chalk was made, and view it with the microscope, it presents +innumerable _Globigerinoe_ embedded in a granular matrix. Thus this deep- +sea mud is substantially chalk. I say substantially, because there are a +good many minor differences; but as these have no bearing on the question +immediately before us,--which is the nature of the _Globigerinoe_ of the +chalk,--it is unnecessary to speak of them. + +_Globigerinoe_ of every size, from the smallest to the largest, are +associated together in the Atlantic mud, and the chambers of many are +filled by a soft animal matter. This soft substance is, in fact, the +remains of the creature to which the _Globigerinoe_ shell, or rather +skeleton, owes its existence--and which is an animal of the simplest +imaginable description. It is, in fact, a mere particle of living jelly, +without defined parts of any kind--without a mouth, nerves, muscles, or +distinct organs, and only manifesting its vitality to ordinary +observation by thrusting out and retracting from all parts of its +surface, long filamentous processes, which serve for arms and legs. Yet +this amorphous particle, devoid of everything which, in the higher +animals, we call organs, is capable of feeding, growing, and multiplying; +of separating from the ocean the small proportion of carbonate of lime +which is dissolved in sea-water; and of building up that substance into a +skeleton for itself, according to a pattern which can be imitated by no +other known agency. + +The notion that animals can live and flourish in the sea, at the vast +depths from which apparently living _Globigerinoe_; have been brought up, +does not agree very well with our usual conceptions respecting the +conditions of animal life; and it is not so absolutely impossible as it +might at first sight appear to be, that the _Globigcrinoe_ of the +Atlantic sea-bottom do not live and die where they are found. + +As I have mentioned, the soundings from the great Atlantic plain are +almost entirely made up of _Globigerinoe_, with the granules which have +been mentioned, and some few other calcareous shells; but a small +percentage of the chalky mud--perhaps at most some five per cent. of it-- +is of a different nature, and consists of shells and skeletons composed +of silex, or pure flint. These silicious bodies belong partly to the +lowly vegetable organisms which are called _Diatomaceoe_, and partly to +the minute, and extremely simple, animals, termed _Radiolaria_. It is +quite certain that these creatures do not live at the bottom of the +ocean, but at its surface--where they may be obtained in prodigious +numbers by the use of a properly constructed net. Hence it follows that +these silicious organisms, though they are not heavier than the lightest +dust, must have fallen, in some cases, through fifteen thousand feet of +water, before they reached their final resting-place on the ocean floor. +And considering how large a surface these bodies expose in proportion to +their weight, it is probable that they occupy a great length of time in +making their burial journey from the surface of the Atlantic to the +bottom. + +But if the _Radiolaria_ and Diatoms are thus rained upon the bottom of +the sea, from the superficial layer of its waters in which they pass +their lives, it is obviously possible that the _Globigerinoe_ may be +similarly derived; and if they were so, it would be much more easy to +understand how they obtain their supply of food than it is at present. +Nevertheless, the positive and negative evidence all points the other +way. The skeletons of the full-grown, deep-sea _Globigerinoe_ are so +remarkably solid and heavy in proportion to their surface as to seem +little fitted for floating; and, as a matter of fact, they are not to be +found along with the Diatoms and _Radiolaria_ in the uppermost stratum of +the open ocean. It has been observed, again, that the abundance of +_Globigerinoe_, in proportion to other organisms, of like kind, increases +with the depth of the sea; and that deep-water _Globigerinoe_ are larger +than those which live in shallower parts of the sea; and such facts +negative the supposition that these organisms have been swept by currents +from the shallows into the deeps of the Atlantic. It therefore seems to +be hardly doubtful that these wonderful creatures live and die at the +depths in which they are found.[2] + +[Footnote 2: During the cruise of H.M.S. _Bulldog_, commanded by Sir +Leopold M'Clintock, in 1860, living star-fish were brought up, clinging +to the lowest part of the sounding-line, from a depth of 1,260 fathoms, +midway between Cape Farewell, in Greenland, and the Rockall banks. Dr. +Wallich ascertained that the sea-bottom at this point consisted of the +ordinary _Globigerina_ ooze, and that the stomachs of the star-fishes +were full of _Globigerinoe_. This discovery removes all objections to the +existence of living _Globigerinoe_ at great depths, which are based upon +the supposed difficulty of maintaining animal life under such conditions; +and it throws the burden of proof upon those who object to the +supposition that the _Globigerinoe_ live and die where they are found.] + +However, the important points for us are, that the living _Globigerinoe_ +are exclusively marine animals, the skeletons of which abound at the +bottom of deep seas; and that there is not a shadow of reason for +believing that the habits of the _Globigerinoe_ of the chalk differed +from those of the existing species. But if this be true, there is no +escaping the conclusion that the chalk itself is the dried mud of an +ancient deep sea. + +In working over the soundings collected by Captain Dayman, I was +surprised to find that many of what I have called the "granules" of that +mud were not, as one might have been tempted to think at first, the more +powder and waste of _Globigerinoe_, but that they had a definite form and +size. I termed these bodies "_coccoliths_," and doubted their organic +nature. Dr. Wallich verified my observation, and added the interesting +discovery that, not unfrequently, bodies similar to these "coccoliths" +were aggregated together into spheroids, which lie termed +"_coccospheres_." So far as we knew, these bodies, the nature of which is +extremely puzzling and problematical, were peculiar to the Atlantic +soundings. But, a few years ago, Mr. Sorby, in making a careful +examination of the chalk by means of thin sections and otherwise, +observed, as Ehrenberg had done before him, that much of its granular +basis possesses a definite form. Comparing these formed particles with +those in the Atlantic soundings, he found the two to be identical; and +thus proved that the chalk, like the surroundings, contains these +mysterious coccoliths and coccospheres. Here was a further and most +interesting confirmation, from internal evidence, of the essential +identity of the chalk with modern deep-sea mud. _Globigerinoe_, +coccoliths, and coccospheres are found as the chief constituents of both, +and testify to the general similarity of the conditions under which both +have been formed.[3] + +[Footnote 3: I have recently traced out the development of the +"coccoliths" from a diameter of 1/7000th of an inch up to their largest +size (which is about 1/1000th), and no longer doubt that they are +produced by independent organisms, which, like the _Globigerinoe_, live +and die at the bottom of the sea.] + +The evidence furnished by the hewing, facing, and superposition of the +stones of the Pyramids, that these structures were built by men, has no +greater weight than the evidence that the chalk was built by +_Globigerinoe_; and the belief that those ancient pyramid-builders were +terrestrial and air-breathing creatures like ourselves, is not better +based than the conviction that the chalk-makers lived in the sea. But as +our belief in the building of the Pyramids by men is not only grounded on +the internal evidence afforded by these structures, but gathers strength +from multitudinous collateral proofs, and is clinched by the total +absence of any reason for a contrary belief; so the evidence drawn from +the _Globigerinoe_ that the chalk is an ancient sea-bottom, is fortified +by innumerable independent lines of evidence; and our belief in the truth +of the conclusion to which all positive testimony tends, receives the +like negative justification from the fact that no other hypothesis has a +shadow of foundation. + +It may be worth while briefly to consider a few of these collateral +proofs that the chalk was deposited at the bottom of the sea. The great +mass of the chalk is composed, as we have seen, of the skeletons of +_Globigerinoe_, and other simple organisms, imbedded in granular matter. +Here and there, however, this hardened mud of the ancient sea reveals the +remains of higher animals which have lived and died, and left their hard +parts in the mud, just as the oysters die and leave their shells behind +them, in the mud of the present seas. + +There are, at the present day, certain groups of animals which are never +found in fresh waters, being unable to live anywhere but in the sea. Such +are the corals; those corallines which are called _Polyzoa_; those +creatures which fabricate the lamp-shells, and are called _Brachiopoda_; +the pearly _Nautilus_, and all animals allied to it; and all the forms of +sea-urchins and star-fishes. Not only are all these creatures confined to +salt water at the present day; but, so far as our records of the past go, +the conditions of their existence have been the same: hence, their +occurrence in any deposit is as strong evidence as can be obtained, that +that deposit was formed in the sea. Now the remains of animals of all the +kinds which have been enumerated, occur in the chalk, in greater or less +abundance; while not one of those forms of shell-fish which are +characteristic of fresh water has yet been observed in it. + +When we consider that the remains of more than three thousand distinct +species of aquatic animals have been discovered among the fossils of the +chalk, that the great majority of them are of such forms as are now met +with only in the sea, and that there is no reason to believe that any one +of them inhabited fresh water--the collateral evidence that the chalk +represents an ancient sea-bottom acquires as great force as the proof +derived from the nature of the chalk itself. I think you will now allow +that I did not overstate my case when I asserted that we have as strong +grounds for believing that all the vast area of dry land, at present +occupied by the chalk, was once at the bottom of the sea, as we have for +any matter of history whatever; while there is no justification for any +other belief. + +No less certain it is that the time during which the countries we now +call south-east England, France, Germany, Poland, Russia, Egypt, Arabia, +Syria, were more or less completely covered by a deep sea, was of +considerable duration. We have already seen that the chalk is, in places, +more than a thousand feet thick. I think you will agree with me, that it +must have taken some time for the skeletons of animalcules of a hundredth +of an inch in diameter to heap up such a mass as that. I have said that +throughout the thickness of the chalk the remains of other animals are +scattered. These remains are often in the most exquisite state of +preservation. The valves of the shell-fishes are commonly adherent; the +long spines of some of the sea-urchins, which would be detached by the +smallest jar, often remain in their places. In a word, it is certain that +these animals have lived and died when the place which they now occupy +was the surface of as much of the chalk as had then been deposited; and +that each has been covered up by the layer of _Globigerina_ mud, upon +which the creatures imbedded a little higher up have, in like manner, +lived and died. But some of these remains prove the existence of reptiles +of vast size in the chalk sea. These lived their time, and had their +ancestors and descendants, which assuredly implies time, reptiles being +of slow growth. + +There is more curious evidence, again, that the process of covering up, +or, in other words, the deposit of _Globigerina_ skeletons, did not go on +very fast. It is demonstrable that an animal of the cretaceous sea might +die, that its skeleton might lie uncovered upon the sea-bottom long +enough to lose all its outward coverings and appendages by putrefaction; +and that, after this had happened, another animal might attach itself to +the dead and naked skeleton, might grow to maturity, and might itself die +before the calcareous mud had buried the whole. + +Cases of this kind are admirably described by Sir Charles Lyell. He +speaks of the frequency with which geologists find in the chalk a +fossilized sea-urchin, to which is attached the lower valve of a +_Crania_. This is a kind of shell-fish, with a shell composed of two +pieces, of which, as in the oyster, one is fixed and the other free. + +"The upper valve is almost invariably wanting, though occasionally found +in a perfect state of preservation in the white chalk at some distance. +In this case, we see clearly that the sea-urchin first lived from youth +to age, then died and lost its spines, which were carried away. Then the +young _Crania_ adhered to the bared shell, grew and perished in its turn; +after which, the upper valve was separated from the lower, before the +Echinus became enveloped in chalky mud."[4] + +A specimen in the Museum of Practical Geology, in London, still further +prolongs the period which must have elapsed between the death of the sea- +urchin, and its burial by the _Globigerinoe_. For the outward face of the +valve of a _Crania_, which is attached to a sea-urchin, (_Micraster_), is +itself overrun by an incrusting coralline, which spreads thence over more +or less of the surface of the sea-urchin. It follows that, after the +upper valve of the _Crania_ fell off, the surface of the attached valve +must have remained exposed long enough to allow of the growth of the +whole coralline, since corallines do not live embedded in mud.[4] + +[Footnote 4: _Elements of Geology_, by Sir Charles Lyell, Bart. F.B.S., +p. 23.] + +The progress of knowledge may, one day, enable us to deduce from such +facts as these the maximum rate at which the chalk can have accumulated, +and thus to arrive at the minimum duration of the chalk period. Suppose +that the valve of the _Cronia_ upon which a coralline has fixed itself in +the way just described, is so attached to the sea-urchin that no part of +it is more than an inch above the face upon which the sea-urchin rests. +Then, as the coralline could not have fixed itself, if the _Crania_ had +been covered up with chalk mud, and could not have lived had itself been +so covered, it follows, that an inch of chalk mud could not have +accumulated within the time between the death and decay of the soft parts +of the sea-urchin and the growth of the coralline to the full size which +it has attained. If the decay of the soft parts of the sea-urchin; the +attachment, growth to maturity, and decay of the _Crania_; and the +subsequent attachment and growth of the coralline, took a year (which is +a low estimate enough), the accumulation of the inch of chalk must have +taken more than a year: and the deposit of a thousand feet of chalk must, +consequently, have taken more than twelve thousand years. + +The foundation of all this calculation is, of course, a knowledge of the +length of time the _Crania_ and the coralline needed to attain their full +size; and, on this head, precise knowledge is at present wanting. But +there are circumstances which tend to show, that nothing like an inch of +chalk has accumulated during the life of a _Crania_; and, on any probable +estimate of the length of that life, the chalk period must have had a +much longer duration than that thus roughly assigned to it. + +Thus, not only is it certain that the chalk is the mud of an ancient sea- +bottom; but it is no less certain, that the chalk sea existed during an +extremely long period, though we may not be prepared to give a precise +estimate of the length of that period in years. The relative duration is +clear, though the absolute duration may not be definable. The attempt to +affix any precise date to the period at which the chalk sea began, or +ended, its existence, is baffled by difficulties of the same kind. But +the relative age of the cretaceous epoch may be determined with as great +ease and certainty as the long duration of that epoch. + +You will have heard of the interesting discoveries recently made, in +various parts of Western Europe, of flint implements, obviously worked +into shape by human hands, under circumstances which show conclusively +that man is a very ancient denizen of these regions. It has been proved +that the whole populations of Europe, whose existence has been revealed +to us in this way, consisted of savages, such as the Esquimaux are now; +that, in the country which is now France, they hunted the reindeer, and +were familiar with the ways of the mammoth and the bison. The physical +geography of France was in those days different from what it is now--the +river Somme, for instance, having cut its bed a hundred feet deeper +between that time and this; and, it is probable, that the climate was +more like that of Canada or Siberia, than that of Western Europe. + +The existence of these people is forgotten even in the traditions of the +oldest historical nations. The name and fame of them had utterly vanished +until a few years back; and the amount of physical change which has been +effected since their day renders it more than probable that, venerable as +are some of the historical nations, the workers of the chipped flints of +Hoxne or of Amiens are to them, as they are to us, in point of antiquity. +But, if we assign to these hoar relics of long-vanished generations of +men the greatest age that can possibly be claimed for them, they are not +older than the drift, or boulder clay, which, in comparison with the +chalk, is but a very juvenile deposit. You need go no further than your +own sea-board for evidence of this fact. At one of the most charming +spots on the coast of Norfolk, Cromer, you will see the boulder clay +forming a vast mass, which lies upon the chalk, and must consequently +have come into existence after it. Huge boulders of chalk are, in fact, +included in the clay, and have evidently been brought to the position +they now occupy by the same agency as that which has planted blocks of +syenite from Norway side by side with them. + +The chalk, then, is certainly older than the boulder clay. If you ask how +much, I will again take you no further than the same spot upon your own +coasts for evidence. I have spoken of the boulder clay and drift as +resting upon the chalk. That is not strictly true. Interposed between the +chalk and the drift is a comparatively insignificant layer, containing +vegetable matter. But that layer tells a wonderful history. It is full of +stumps of trees standing as they grew. Fir-trees are there with their +cones, and hazel-bushes with their nuts; there stand the stools of oak +and yew trees, beeches and alders. Hence this stratum is appropriately +called the "forest-bed." + +It is obvious that the chalk must have been upheaved and converted into +dry land, before the timber trees could grow upon it. As the bolls of +some of these trees are from two to three feet in diameter, it is no less +clear that the dry land thus formed remained in the same condition for +long ages. And not only do the remains of stately oaks and well-grown +firs testify to the duration of this condition of things, but additional +evidence to the same effect is afforded by the abundant remains of +elephants, rhinoceroses, hippopotamuses, and other great wild beasts, +which it has yielded to the zealous search of such men as the Rev. Mr. +Gunn. When you look at such a collection as he has formed, and bethink +you that these elephantine bones did veritably carry their owners about, +and these great grinders crunch, in the dark woods of which the forest- +bed is now the only trace, it is impossible not to feel that they are as +good evidence of the lapse of time as the annual rings of the tree +stumps. + +Thus there is a writing upon the wall of cliffs at Cromer, and whoso runs +may read it. It tells us, with an authority which cannot be impeached, +that the ancient sea-bed of the chalk sea was raised up, and remained dry +land, until it was covered with forest, stocked with the great game the +spoils of which have rejoiced your geologists. How long it remained in +that condition cannot be said; but "the whirligig of time brought its +revenges" in those days as in these. That dry land, with the bones and +teeth of generations of long-lived elephants, hidden away among the +gnarled roots and dry leaves of its ancient trees, sank gradually to the +bottom of the icy sea, which covered it with huge masses of drift and +boulder clay. Sea-beasts, such as the walrus, now restricted to the +extreme north, paddled about where birds had twittered among the topmost +twigs of the fir-trees. How long this state of things endured we know +not, but at length it came to an end. The upheaved glacial mud hardened +into the soil of modern Norfolk. Forests grew once more, the wolf and the +beaver replaced the reindeer and the elephant; and at length what we call +the history of England dawned. + +Thus you have, within the limits of your own county, proof that the chalk +can justly claim a very much greater antiquity than even the oldest +physical traces of mankind. But we may go further and demonstrate, by +evidence of the same authority as that which testifies to the existence +of the father of men, that the chalk is vastly older than Adam himself. +The Book of Genesis informs us that Adam, immediately upon his creation, +and before the appearance of Eve, was placed in the Garden of Eden. The +problem of the geographical position of Eden has greatly vexed the +spirits of the learned in such matters, but there is one point respecting +which, so far as I know, no commentator has ever raised a doubt. This is, +that of the four rivers which are said to run out of it, Euphrates and +Hiddekel are identical with the rivers now known by the names of +Euphrates and Tigris. But the whole country in which these mighty rivers +take their origin, and through which they run, is composed of rocks which +are either of the same age as the chalk, or of later date. So that the +chalk must not only have been formed, but, after its formation, the time +required for the deposit of these later rocks, and for their upheaval +into dry land, must have elapsed, before the smallest brook which feeds +the swift stream of "the great river, the river of Babylon," began to +flow. + + +Thus, evidence which cannot be rebutted, and which need not be +strengthened, though if time permitted I might indefinitely increase its +quantity, compels you to believe that the earth, from the time of the +chalk to the present day, has been the theatre of a series of changes as +vast in their amount, as they were slow in their progress. The area on +which we stand has been first sea and then land, for at least four +alternations; and has remained in each of these conditions for a period +of great length. + +Nor have these wonderful metamorphoses of sea into land, and of land into +sea, been confined to one corner of England. During the chalk period, or +"cretaceous epoch," not one of the present great physical features of the +globe was in existence. Our great mountain ranges, Pyrenees, Alps, +Himalayas, Andes, have all been upheaved since the chalk was deposited, +and the cretaceous sea flowed over the sites of Sinai and Ararat. All +this is certain, because rocks of cretaceous, or still later, date have +shared in the elevatory movements which gave rise to these mountain +chains; and may be found perched up, in some cases, many thousand feet +high upon their flanks. And evidence of equal cogency demonstrates that, +though, in Norfolk, the forest-bed rests directly upon the chalk, yet it +does so, not because the period at which the forest grew immediately +followed that at which the chalk was formed, but because an immense lapse +of time, represented elsewhere by thousands of feet of rock, is not +indicated at Cromer. + +I must ask you to believe that there is no less conclusive proof that a +still more prolonged succession of similar changes occurred, before the +chalk was deposited. Nor have we any reason to think that the first term +in the series of these changes is known. The oldest sea-beds preserved to +us are sands, and mud, and pebbles, the wear and tear of rocks which were +formed in still older oceans. + +But, great as is the magnitude of these physical changes of the world, +they have been accompanied by a no less striking series of modifications +in its living inhabitants. All the great classes of animals, beasts of +the field, fowls of the air, creeping things, and things which dwell in +the waters, flourished upon the globe long ages before the chalk was +deposited. Very few, however, if any, of these ancient forms of animal +life were identical with those which now live. Certainly not one of the +higher animals was of the same species as any of those now in existence. +The beasts of the field, in the days before the chalk, were not our +beasts of the field, nor the fowls of the air such as those which the eye +of men has seen flying, unless his antiquity dates infinitely further +back than we at present surmise. If we could be carried back into those +times, we should be as one suddenly set down in Australia before it was +colonized. We should see mammals, birds, reptiles, fishes, insects, +snails, and the like, clearly recognizable as such, and yet not one of +them would be just the same as those with which we are familiar, and many +would be extremely different. + +From that time to the present, the population of the world has undergone +slow and gradual, but incessant, changes. There has been no grand +catastrophe--no destroyer has swept away the forms of life of one period, +and replaced them by a totally new creation: but one species has vanished +and another has taken its place; creatures of one type of structure have +diminished, those of another have increased, as time has passed on. And +thus, while the differences between the living creatures of the time +before the chalk and those of the present day appear startling, if placed +side by side, we are led from one to the other by the most gradual +progress, if we follow the course of Nature through the whole series of +those relics of her operations which she has left behind. It is by the +population of the chalk sea that the ancient and the modern inhabitants +of the world are most completely connected. The groups which are dying +out flourish, side by side, with the groups which are now the dominant +forms of life. Thus the chalk contains remains of those strange flying +and swimming reptiles, the pterodactyl, the ichthyosaurus, and the +plesiosaurus, which are found in no later deposits, but abounded in +preceding ages. The chambered shells called ammonites and belemnites, +which are so characteristic of the period preceding the cretaceous, in +like manner die with it. + +But, amongst these fading remainders of a previous state of things, are +some very modern forms of life, looking like Yankee pedlars among a tribe +of Red Indians. Crocodiles of modern type appear; bony fishes, many of +them very similar to existing species, almost supplant the forms of fish +which predominate in more ancient seas; and many kinds of living shell- +fish first become known to us in the chalk. The vegetation acquires a +modern aspect. A few living animals are not even distinguishable as +species, from those which existed at that remote epoch. The _Globigerina_ +of the present day, for example, is not different specifically from that +of the chalk; and the same maybe said of many other _Foraminifera_. I +think it probable that critical and unprejudiced examination will show +that more than one species of much higher animals have had a similar +longevity; but the only example which I can at present give confidently +is the snake's-head lampshell (_Terebratulina caput serpentis_), which +lives in our English seas and abounded (as _Terebratulina striata_ of +authors) in the chalk. + +The longest line of human ancestry must hide its diminished head before +the pedigree of this insignificant shell-fish. We Englishmen are proud to +have an ancestor who was present at the Battle of Hastings. The ancestors +of _Terebratulina caput serpentis_ may have been present at a battle of +_Ichthyosauria_ in that part of the sea which, when the chalk was +forming, flowed over the site of Hastings. While all around has changed, +this _Terebratulina_ has peacefully propagated its species from +generation to generation, and stands to this day, as a living testimony +to the continuity of the present with the past history of the globe. + + +Up to this moment I have stated, so far as I know, nothing but well- +authenticated facts, and the immediate conclusions which they force upon +the mind. But the mind is so constituted that it does not willingly rest +in facts and immediate causes, but seeks always after a knowledge of the +remoter links in the chain of causation. + +Taking the many changes of any given spot of the earth's surface, from +sea to land and from land to sea, as an established fact, we cannot +refrain from asking ourselves how these changes have occurred. And when +we have explained them--as they must be explained--by the alternate slow +movements of elevation and depression which have affected the crust of +the earth, we go still further back, and ask, Why these movements? + +I am not certain that any one can give you a satisfactory answer to that +question. Assuredly I cannot. All that can be said, for certain, is, that +such movements are part of the ordinary course of nature, inasmuch as +they are going on at the present time. Direct proof may be given, that +some parts of the land of the northern hemisphere are at this moment +insensibly rising and others insensibly sinking; and there is indirect, +but perfectly satisfactory, proof, that an enormous area now covered by +the Pacific has been deepened thousands of feet, since the present +inhabitants of that sea came into existence. Thus there is not a shadow +of a reason for believing that the physical changes of the globe, in past +times, have been effected by other than natural causes. Is there any more +reason for believing that the concomitant modifications in the forms of +the living inhabitants of the globe have been brought about in other +ways? + +Before attempting to answer this question, let us try to form a distinct +mental picture of what has happened in some special case. The crocodiles +are animals which, as a group, have a very vast antiquity. They abounded +ages before the chalk was deposited; they throng the rivers in warm +climates, at the present day. There is a difference in the form of the +joints of the back-bone, and in some minor particulars, between the +crocodiles of the present epoch and those which lived before the chalk; +but, in the cretaceous epoch, as I have already mentioned, the crocodiles +had assumed the modern type of structure. Notwithstanding this, the +crocodiles of the chalk are not identically the same as those which lived +in the times called "older tertiary," which succeeded the cretaceous +epoch; and the crocodiles of the older tertiaries are not identical with +those of the newer tertiaries, nor are these identical with existing +forms. I leave open the question whether particular species may have +lived on from epoch to epoch. But each epoch has had its peculiar +crocodiles; though all, since the chalk, have belonged to the modern +type, and differ simply in their proportions, and in such structural +particulars as are discernible only to trained eyes. + +How is the existence of this long succession of different species of +crocodiles to be accounted for? Only two suppositions seem to be open to +us--Either each species of crocodile has been specially created, or it +has arisen out of some pre-existing form by the operation of natural +causes. Choose your hypothesis; I have chosen mine. I can find no +warranty for believing in the distinct creation of a score of successive +species of crocodiles in the course of countless ages of time. Science +gives no countenance to such a wild fancy; nor can even the perverse +ingenuity of a commentator pretend to discover this sense, in the simple +words in which the writer of Genesis records the proceedings of the fifth +and six days of the Creation. + +On the other hand, I see no good reason for doubting the necessary +alternative, that all these varied species have been evolved from pre- +existing crocodilian forms, by the operation of causes as completely a +part of the common order of nature as those which have effected the +changes of the inorganic world. Few will venture to affirm that the +reasoning which applies to crocodiles loses its force among other +animals, or among plants. If one series of species has come into +existence by the operation of natural causes, it seems folly to deny that +all may have arisen in the same way. + +A small beginning has led us to a great ending. If I were to put the bit +of chalk with which we started into the hot but obscure flame of burning +hydrogen, it would presently shine like the sun. It seems to me that this +physical metamorphosis is no false image of what has been the result of +our subjecting it to a jet of fervent, though nowise brilliant, thought +to-night. It has become luminous, and its clear rays, penetrating the +abyss of the remote past, have brought within our ken some stages of the +evolution of the earth. And in the shifting "without haste, but without +rest" of the land and sea, as in the endless variation of the forms +assumed by living beings, we have observed nothing but the natural +product of the forces originally possessed by the substance of the +universe. + + + +II + + +THE PROBLEMS OF THE DEEP SEA + +[1873] + +On the 21st of December, 1872, H.M.S. _Challenger_, an eighteen gun +corvette, of 2,000 tons burden, sailed from Portsmouth harbour for a +three, or perhaps four, years' cruise. No man-of-war ever left that +famous port before with so singular an equipment. Two of the eighteen +sixty-eight pounders of the _Challenger's_ armament remained to enable +her to speak with effect to sea-rovers, haply devoid of any respect for +science, in the remote seas for which she is bound; but the main-deck +was, for the most part, stripped of its war-like gear, and fitted up with +physical, chemical, and biological laboratories; Photography had its dark +cabin; while apparatus for dredging, trawling, and sounding; for +photometers and for thermometers, filled the space formerly occupied by +guns and gun-tackle, pistols and cutlasses. + +The crew of the _Challenger_ match her fittings. Captain Nares, his +officers and men, are ready to look after the interests of hydrography, +work the ship, and, if need be, fight her as seamen should; while there +is a staff of scientific civilians, under the general direction of Dr. +Wyville Thomson, F.R.S. (Professor of Natural History in Edinburgh +University by rights, but at present detached for duty _in partibus_), +whose business it is to turn all the wonderfully packed stores of +appliances to account, and to accumulate, before the ship returns to +England, such additions to natural knowledge as shall justify the labour +and cost involved in the fitting out and maintenance of the expedition. + +Under the able and zealous superintendence of the Hydrographer, Admiral +Richards, every precaution which experience and forethought could devise +has been taken to provide the expedition with the material conditions of +success; and it would seem as if nothing short of wreck or pestilence, +both most improbable contingencies, could prevent the _Challenger_ from +doing splendid work, and opening up a new era in the history of +scientific voyages. + +The dispatch of this expedition is the culmination of a series of such +enterprises, gradually increasing in magnitude and importance, which the +Admiralty, greatly to its credit, has carried out for some years past; +and the history of which is given by Dr. Wyville Thomson in the +beautifully illustrated volume entitled "The Depths of the Sea," +published since his departure. + +"In the spring of the year 1868, my friend Dr. W.B. Carpenter, at that +time one of the Vice-Presidents of the Royal Society, was with me in +Ireland, where we were working out together the structure and development +of the Crinoids. I had long previously had a profound conviction that the +land of promise for the naturalist, the only remaining region where there +were endless novelties of extraordinary interest ready to the hand which +had the means of gathering them, was the bottom of the deep sea. I had +even had a glimpse of some of these treasures, for I had seen, the year +before, with Prof. Sars, the forms which I have already mentioned dredged +by his son at a depth of 300 to 400 fathoms off the Loffoten Islands. I +propounded my views to my fellow-labourer, and we discussed the subject +many times over our microscopes. I strongly urged Dr. Carpenter to use +his influence at head-quarters to induce the Admiralty, probably through +the Council of the Royal Society, to give us the use of a vessel properly +fitted with dredging gear and all necessary scientific apparatus, that +many heavy questions as to the state of things in the depths of the +ocean, which were still in a state of uncertainty, might be definitely +settled. After full consideration, Dr. Carpenter promised his hearty co- +operation, and we agreed that I should write to him on his return to +London, indicating generally the results which I anticipated, and +sketching out what I conceived to be a promising line of inquiry. The +Council of the Royal Society warmly supported the proposal; and I give +here in chronological order the short and eminently satisfactory +correspondence which led to the Admiralty placing at the disposal of Dr. +Carpenter and myself the gunboat _Lightninq_, under the command of Staff- +Commander May, R.N., in the summer of 1868, for a trial cruise to the +North of Scotland, and afterwards to the much wider surveys in H.M.S. +_Porcupine_, Captain Calver, R.N., which were made with the additional +association of Mr. Gwyn Jeffreys, in the summers of the years 1869 and +1870."[1] + +[Footnote 1: The Depths of the Sea, pp. 49-50.] + +Plain men may be puzzled to understand why Dr. Wyville Thomson, not being +a cynic, should relegate the "Land of Promise" to the bottom of the deep +sea, they may still more wonder what manner of "milk and honey" the +_Challenger_ expects to find; and their perplexity may well rise to its +maximum, when they seek to divine the manner in which that milk and honey +are to be got out of so inaccessible a Canaan. I will, therefore, +endeavour to give some answer to these questions in an order the reverse +of that in which I have stated them. + +Apart from hooks, and lines, and ordinary nets, fishermen have, from time +immemorial, made use of two kinds of implements for getting at sea- +creatures which live beyond tide-marks--these are the "dredge" and the +"trawl." The dredge is used by oyster-fishermen. Imagine a large bag, the +mouth of which has the shape of an elongated parallelogram, and is +fastened to an iron frame of the same shape, the two long sides of this +rim being fashioned into scrapers. Chains attach the ends of the frame to +a stout rope, so that when the bag is dragged along by the rope the edge +of one of the scrapers rests on the ground, and scrapes whatever it +touches into the bag. The oyster-dredger takes one of these machines in +his boat, and when he has reached the oyster-bed the dredge is tossed +overboard; as soon as it has sunk to the bottom the rope is paid out +sufficiently to prevent it from pulling the dredge directly upwards, and +is then made fast while the boat goes ahead. The dredge is thus dragged +along and scrapes oysters and other sea-animals and plants, stones, and +mud into the bag. When the dredger judges it to be full he hauls it up, +picks out the oysters, throws the rest overboard, and begins again. + +Dredging in shallow water, say ten to twenty fathoms, is an easy +operation enough; but the deeper the dredger goes, the heavier must be +his vessel, and the stouter his tackle, while the operation of hauling up +becomes more and more laborious. Dredging in 150 fathoms is very hard +work, if it has to be carried on by manual labour; but by the use of the +donkey-engine to supply power,[2] and of the contrivances known as +"accumulators," to diminish the risk of snapping the dredge rope by the +rolling and pitching of the vessel, the dredge has been worked deeper and +deeper, until at last, on the 22nd of July, 1869, H.M.S. _Porcupine_ +being in the Bay of Biscay, Captain Calver, her commander, performed the +unprecedented feat of dredging in 2,435 fathoms, or 14,610 feet, a depth +nearly equal to the height of Mont Blanc. The dredge "was rapidly hauled +on deck at one o'clock in the morning of the 23rd, after an absence of +7-1/4 hours, and a journey of upwards of eight statute miles," with a +hundred weight and a half of solid contents. + +[Footnote 2: The emotional side of the scientific nature has its +singularities. Many persons will call to mind a certain philosopher's +tenderness over his watch--"the little creature"--which was so singularly +lost and found again. But Dr. Wyville Thomson surpasses the owner of the +watch in his loving-kindness towards a donkey-engine. "This little engine +was the comfort of our lives. Once or twice it was overstrained, and then +we pitied the willing little thing, panting like an overtaxed horse."] + +The trawl is a sort of net for catching those fish which habitually live +at the bottom of the sea, such as soles, plaice, turbot, and gurnett. The +mouth of the net may be thirty or forty feet wide, and one edge of its +mouth is fastened to a beam of wood of the same length. The two ends of +the beam are supported by curved pieces of iron, which raise the beam and +the edge of the net which is fastened to it, for a short distance, while +the other edge of the mouth of the net trails upon the ground. The closed +end of the net has the form of a great pouch; and, as the beam is dragged +along, the fish, roused from the bottom by the sweeping of the net, +readily pass into its mouth and accumulate in the pouch at its end. After +drifting with the tide for six or seven hours the trawl is hauled up, the +marketable fish are picked out, the others thrown away, and the trawl +sent overboard for another operation. + +More than a thousand sail of well-found trawlers are constantly engaged +in sweeping the seas around our coast in this way, and it is to them that +we owe a very large proportion of our supply of fish. The difficulty of +trawling, like that of dredging, rapidly increases with the depth at +which the operation is performed; and, until the other day, it is +probable that trawling at so great a depth as 100 fathoms was something +unheard of. But the first news from the _Challenger_ opens up new +possibilities for the trawl. + +Dr. Wyville Thomson writes ("Nature," March 20, 1873):-- + +"For the first two or three hauls in very deep water off the coast of +Portugal, the dredge came up filled with the usual 'Atlantic ooze,' +tenacious and uniform throughout, and the work of hours, in sifting, gave +the very smallest possible result. We were extremely anxious to get some +idea of the general character of the Fauna, and particularly of the +distribution of the higher groups; and after various suggestions for +modification of the dredge, it was proposed to try the ordinary trawl. We +had a compact trawl, with a 15-feet beam, on board, and we sent it down +off Cape St. Vincent at a depth of 600 fathoms. The experiment looked +hazardous, but, to our great satisfaction, the trawl came up all right +and contained, with many of the larger invertebrate, several fishes.... +After the first attempt we tried the trawl several times at depths of +1090, 1525, and, finally, 2125 fathoms, and always with success." + +To the coral-fishers of the Mediterranean, who seek the precious red +coral, which grows firmly fixed to rocks at a depth of sixty to eighty +fathoms, both the dredge and the trawl would be useless. They, therefore, +have recourse to a sort of frame, to which are fastened long bundles of +loosely netted hempen cord, and which is lowered by a rope to the depth +at which the hempen cords can sweep over the surface of the rocks and +break off the coral, which is brought up entangled in the cords. A +similar contrivance has arisen out of the necessities of deep-sea +exploration. + +In the course of the dredging of the _Porcupine_, it was frequently found +that, while few objects of interest were brought up within the dredge, +many living creatures came up sticking to the outside of the dredge-bag, +and even to the first few fathoms of the dredge-rope. The mouth of the +dredge doubtless rapidly filled with mud, and thus the things it should +have brought up were shut out. To remedy this inconvenience Captain +Calver devised an arrangement not unlike that employed by the coral- +fishers. He fastened half a dozen swabs, such as are used for drying +decks, to the dredge. A swab is something like what a birch-broom would +be if its twigs were made of long, coarse, hempen yarns. These dragged +along after the dredge over the surface of the mud, and entangled the +creatures living there--multitudes of which, twisted up in the strands of +the swabs, were brought to the surface with the dredge. A further +improvement was made by attaching a long iron bar to the bottom of the +dredge bag, and fastening large bunches of teased-out hemp to the end of +this bar. These "tangles" bring up immense quantities of such animals as +have long arms, or spines, or prominences which readily become caught in +the hemp, but they are very destructive to the fragile organisms which +they imprison; and, now that the trawl can be successfully worked at the +greatest depths, it may be expected to supersede them; at least, wherever +the ground is soft enough to permit of trawling. + +It is obvious that between the dredge, the trawl, and the tangles, there +is little chance for any organism, except such as are able to burrow +rapidly, to remain safely at the bottom of any part of the sea which the +_Challenger_ undertakes to explore. And, for the first time in the +history of scientific exploration, we have a fair chance of learning what +the population of the depths of the sea is like in the most widely +different parts of the world. + +And now arises the next question. The means of exploration being fairly +adequate, what forms of life may be looked for at these vast depths? + +The systematic study of the Distribution of living beings is the most +modern branch of Biological Science, and came into existence long after +Morphology and Physiology had attained a considerable development. This +naturally does not imply that, from the time men began to observe natural +phenomena, they were ignorant of the fact that the animals and plants of +one part of the world are different from those in other regions; or that +those of the hills are different from those of the plains in the same +region; or finally that some marine creatures are found only in the +shallows, while others inhabit the deeps. Nevertheless, it was only after +the discovery of America that the attention of naturalists was powerfully +drawn to the wonderful differences between the animal population of the +central and southern parts of the new world and that of those parts of +the old world which lie under the same parallels of latitude. So far back +as 1667 Abraham Mylius, in his treatise "De Animalium origine et +migratione, populorum," argues that, since there are innumerable species +of animals in America which do not exist elsewhere, they must have been +made and placed there by the Deity: Buffon no less forcibly insists upon +the difference between the Faunae of the old and new world. But the first +attempt to gather facts of this order into a whole, and to coordinate +them into a series of generalizations, or laws of Geographical +Distribution, is not a century old, and is contained in the "Specimen +Zoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens," +published, in 1777, by the learned Brunswick Professor, Eberhard +Zimmermann, who illustrates his work by what he calls a "Tabula +Zoographica," which is the oldest distributional map known to me. + +In regard to matters of fact, Zimmermann's chief aim is to show that +among terrestrial mammals, some occur all over the world, while others +are restricted to particular areas of greater or smaller extent; and that +the abundance of species follows temperature, being greatest in warm and +least in cold climates. But marine animals, he thinks, obey no such law. +The Arctic and Atlantic seas, he says, are as full of fishes and other +animals as those of the tropics. It is, therefore, clear that cold does +not affect the dwellers in the sea as it does land animals, and that this +must be the case follows from the fact that sea water, "propter varias +quas continet bituminis spiritusque particulas," freezes with much more +difficulty than fresh water. On the other hand, the heat of the +Equatorial sun penetrates but a short distance below the surface of the +ocean. Moreover, according to Zimmermann, the incessant disturbance of +the mass of the sea by winds and tides, so mixes up the warm and the cold +that life is evenly diffused and abundant throughout the ocean. + +In 1810, Risso, in his work on the Ichthyology of Nice, laid the +foundation of what has since been termed "bathymetrical" distribution, or +distribution in depth, by showing that regions of the sea bottom of +different depths could be distinguished by the fishes which inhabit them. +There was the _littoral region_ between tide marks with its sand-eels, +pipe fishes, and blennies: the _seaweed region_, extending from low- +water-mark to a depth of 450 feet, with its wrasses, rays, and flat fish; +and the _deep-sea region_, from 450 feet to 1500 feet or more, with +its file-fish, sharks, gurnards, cod, and sword-fish. + +More than twenty years later, M.M. Audouin and Milne Edwards carried out +the principle of distinguishing the Faunae of different zones of depth +much more minutely, in their "Recherches pour servir a l'Histoire +Naturelle du Littoral de la France," published in 1832. + +They divide the area included between highwater-mark and lowwater-mark of +spring tides (which is very extensive, on account of the great rise and +fall of the tide on the Normandy coast about St. Malo, where their +observations were made) into four zones, each characterized by its +peculiar invertebrate inhabitants. Beyond the fourth region they +distinguish a fifth, which is never uncovered, and is inhabited by +oysters, scallops, and large starfishes and other animals. Beyond this +they seem to think that animal life is absent.[3] + +[Footnote 3: "Enfin plus has encore, c'est-a-dire alors loin des cotes, +le fond des eaux ne parait plus etre habite, du moms dans nos mers, par +aucun de ces animaux" (1. c. tom. i. p. 237). The "ces animaux" leaves +the meaning of the authors doubtful.] + +Audouin and Milne Edwards were the first to see the importance of the +bearing of a knowledge of the manner in which marine animals are +distributed in depth, on geology. They suggest that, by this means, it +will be possible to judge whether a fossiliferous stratum was formed upon +the shore of an ancient sea, and even to determine whether it was +deposited in shallower or deeper water on that shore; the association of +shells of animals which live in different zones of depth will prove that +the shells have been transported into the position in which they are +found; while, on the other hand, the absence of shells in a deposit will +not justify the conclusion that the waters in which it was formed were +devoid of animal inhabitants, inasmuch as they might have been only too +deep for habitation. + +The new line of investigation thus opened by the French naturalists was +followed up by the Norwegian, Sars, in 1835, by Edward Forbes, in our own +country, in 1840,[4] and by Oersted, in Denmark, a few years later. The +genius of Forbes, combined with his extensive knowledge of botany, +invertebrate zoology, and geology, enabled him to do more than any of his +compeers, in bringing the importance of distribution in depth into +notice; and his researches in the Aegean Sea, and still more his +remarkable paper "On the Geological Relations of the existing Fauna and +Flora of the British Isles," published in 1846, in the first volume of +the "Memoirs of the Geological Survey of Great Britain," attracted +universal attention. + +[Footnote 4: In the paper in the _Memoirs of the Survey_ cited further +on, Forbes writes:-- + +"In an essay 'On the Association of Mollusca on the British Coasts, +considered with reference to Pleistocene Geology,' printed in [the +_Edinburgh Academic Annual_ for] 1840, I described the mollusca, as +distributed on our shores and seas, in four great zones or regions, +usually denominated 'The Littoral zone,' 'The region of Laminariae,' 'The +region of Coral-lines,' and 'The region of Corals.' An extensive series +of researches, chiefly conducted by the members of the committee +appointed by the British Association to investigate the marine geology of +Britain by means of the dredge, have not invalidated this classification, +and the researches of Professor Loven, in the Norwegian and Lapland seas, +have borne out their correctness The first two of the regions above +mentioned had been previously noticed by Lamoureux, in his account of the +distribution (vertically) of sea-weeds, by Audouin and Milne Edwards in +their _Observations on the Natural History of the coast of France_, and +by Sars in the preface to his _Beskrivelser og Jagttayelser_."] + +On the coasts of the British Islands, Forbes distinguishes four zones or +regions, the Littoral (between tide marks), the Laminarian (between +lowwater-mark and 15 fathoms), the Coralline (from 15 to 50 fathoms), and +the Deep sea or Coral region (from 50 fathoms to beyond 100 fathoms). +But, in the deeper waters of the Aegean Sea, between the shore and a depth +of 300 fathoms, Forbes was able to make out no fewer than eight zones of +life, in the course of which the number and variety of forms gradually +diminished until, beyond 300 fathoms, life disappeared altogether. Hence +it appeared as if descent in the sea had much the same effect on life, as +ascent on land. Recent investigations appear to show that Forbes was +right enough in his classification of the facts of distribution in depth +as they are to be observed in the Aegean; and though, at the time he +wrote, one or two observations were extant which might have warned him +not to generalize too extensively from his Aegean experience, his own +dredging work was so much more extensive and systematic than that of any +other naturalist, that it is not wonderful he should have felt justified +in building upon it. Nevertheless, so far as the limit of the range of +life in depth goes, Forbes' conclusion has been completely negatived, and +the greatest depths yet attained show not even an approach to a "zero of +life":-- + +"During the several cruises of H.M. ships _Lightning_ and _Porcupine_ in +the years 1868, 1869, and 1870," says Dr. Wyville Thomson, "fifty-seven +hauls of the dredge were taken in the Atlantic at depths beyond 500 +fathoms, and sixteen at depths beyond 1,000 fathoms, and, in all cases, +life was abundant. In 1869, we took two casts in depths greater than +2,000 fathoms. In both of these life was abundant; and with the deepest +cast, 2,435 fathoms, off the month of the Bay of Biscay, we took living, +well-marked and characteristic examples of all the five invertebrate sub- +kingdoms. And thus the question of the existence of abundant animal life +at the bottom of the sea has been finally settled and for all depths, for +there is no reason to suppose that the depth anywhere exceeds between +three and four thousand fathoms; and if there be nothing in the +conditions of a depth of 2,500 fathoms to prevent the full development of +a varied Fauna, it is impossible to suppose that even an additional +thousand fathoms would make any great difference."[5] + +[Footnote 5: _The Depths of the Sea_, p. 30. Results of a similar kind, +obtained by previous observers, are stated at length in the sixth +chapter, pp. 267-280. The dredgings carried out by Count Pourtales, under +the authority of Professor Peirce, the Superintendent of the United +States Coast Survey, in the years 1867, 1868, and 1869, are particularly +noteworthy, and it is probably not too much to say, in the words of +Professor Agassiz, "that we owe to the coast survey the first broad and +comprehensive basis for an exploration of the sea bottom on a large +scale, opening a new era in zoological and geological research."] + +As Dr. Wyville Thomson's recent letter, cited above, shows, the use of +the trawl, at great depths, has brought to light a still greater +diversity of life. Fishes came up from a depth of 600 to more than 1,000 +fathoms, all in a peculiar condition from the expansion of the air +contained in their bodies. On their relief from the extreme pressure, +their eyes, especially, had a singular appearance, protruding like great +globes from their heads. Bivalve and univalve mollusca seem to be rare at +the greatest depths; but starfishes, sea urchins and other echinoderms, +zoophytes, sponges, and protozoa abound. + +It is obvious that the _Challenger_ has the privilege of opening a new +chapter in the history of the living world. She cannot send down her +dredges and her trawls into these virgin depths of the great ocean +without bringing up a discovery. Even though the thing itself may be +neither "rich nor rare," the fact that it came from that depth, in that +particular latitude and longitude, will be a new fact in distribution, +and, as such, have a certain importance. + +But it may be confidently assumed that the things brought up will very +frequently be zoological novelties; or, better still, zoological +antiquities, which, in the tranquil and little-changed depths of the +ocean, have escaped the causes of destruction at work in the shallows, +and represent the predominant population of a past age. + +It has been seen that Audouin and Milne Edwards foresaw the general +influence of the study of distribution in depth upon the interpretation +of geological phenomena. Forbes connected the two orders of inquiry still +more closely; and in the thoughtful essay "On the connection between the +distribution of the existing Fauna and Flora of the British Isles, and +the geological changes which have affected their area, especially during +the epoch of the Northern drift," to which reference has already been +made, he put forth a most pregnant suggestion. + +In certain parts of the sea bottom in the immediate vicinity of the +British Islands, as in the Clyde district, among the Hebrides, in the +Moray Firth, and in the German Ocean, there are depressed areas, forming a +kind of submarine valleys, the centres of which are from 80 to 100 +fathoms, or more, deep. These depressions are inhabited by assemblages of +marine animals, which differ from those found over the adjacent and +shallower region, and resemble those which are met with much farther +north, on the Norwegian coast. Forbes called these Scandinavian +detachments "Northern outliers." + +How did these isolated patches of a northern population get into these +deep places? To explain the mystery, Forbes called to mind the fact that, +in the epoch which immediately preceded the present, the climate was much +colder (whence the name of "glacial epoch" applied to it); and that the +shells which are found fossil, or sub-fossil, in deposits of that age are +precisely such as are now to be met with only in the Scandinavian, or +still more Arctic, regions. Undoubtedly, during the glacial epoch, the +general population of our seas had, universally, the northern aspect +which is now presented only by the "northern outliers"; just as the +vegetation of the land, down to the sea-level, had the northern character +which is, at present, exhibited only by the plants which live on the tops +of our mountains. But, as the glacial epoch passed away, and the present +climatal conditions were developed, the northern plants were able to +maintain themselves only on the bleak heights, on which southern forms +could not compete with them. And, in like manner, Forbes suggested that, +after the glacial epoch, the northern animals then inhabiting the sea +became restricted to the deeps in which they could hold their own against +invaders from the south, better fitted than they to flourish in the +warmer waters of the shallows. Thus depth in the sea corresponded in its +effect upon distribution to height on the land. + +The same idea is applied to the explanation of a similar anomaly in the +Fauna of the Aegean:-- + +"In the deepest of the regions of depth of the Aegean, the representation +of a Northern Fauna is maintained, partly by identical and partly by +representative forms.... The presence of the latter is essentially due to +the law (of representation of parallels of latitude by zones of depth), +whilst that of the former species depended on their transmission from +their parent seas during a former epoch, and subsequent isolation. That +epoch was doubtless the newer Pliocene or Glacial Era, when the _Mya +truncata_ and other northern forms now extinct in the Mediterranean, and +found fossil in the Sicilian tertiaries, ranged into that sea. The +changes which there destroyed the _shallow water_ glacial forms, did not +affect those living in the depths, and which still survive."[6] + +[Footnote 6: _Memoirs of the Geological Survey of Great Britain_, Vol. i. +p. 390.] + +The conception that the inhabitants of local depressions of the sea +bottom might be a remnant of the ancient population of the area, which +had held their own in these deep fastnesses against an invading Fauna, as +Britons and Gaels have held out in Wales and in Scotland against +encroaching Teutons, thus broached by Forbes, received a wider +application than Forbes had dreamed of when the sounding machine first +brought up specimens of the mud of the deep sea. As I have pointed out +elsewhere,[7] it at once became obvious that the calcareous sticky mud of +the Atlantic was made up, in the main, of shells of _Globigerina_ and +other _Foraminifera_, identical with those of which the true chalk is +composed, and the identity extended even to the presence of those +singular bodies, the Coccoliths and Coccospheres, the true nature of +which is not yet made out. Here then were organisms, as old as the +cretaceous epoch, still alive, and doing their work of rock-making at the +bottom of existing seas. What if _Globigerina_ and the Coccoliths should +not be the only survivors of a world passed away, which are hidden +beneath three miles of salt water? The letter which Dr. Wyville Thomson +wrote to Dr. Carpenter in May, 1868, out of which all these expeditions +have grown, shows that this query had become a practical problem in Dr. +Thomson's mind at that time; and the desirableness of solving the problem +is put in the foreground of his reasons for urging the Government to +undertake the work of exploration:-- + +[Footnote 7: See above, "On a Piece of Chalk," p. 13.] + +"Two years ago, M. Sars, Swedish Government Inspector of Fisheries, had +an opportunity, in his official capacity, of dredging off the Loffoten +Islands at a depth of 300 fathoms. I visited Norway shortly after his +return, and had an opportunity of studying with his father, Professor +Sars, some of his results. Animal forms were _abundant_; many of them +were new to science; and among them was one of surpassing interest, the +small crinoid, of which you have a specimen, and which we at once +recognised as a degraded type of the _Apiocrinidoe_, an order hitherto +regarded as extinct, which attained its maximum in the Pear Encrinites of +the Jurassic period, and whose latest representative hitherto known was +the _Bourguettocrinus_ of the chalk. Some years previously, Mr. +Absjornsen, dredging in 200 fathoms in the Hardangerfjord, procured +several examples of a Starfish (_Brisinga_), which seems to find its +nearest ally in the fossil genus _Protaster_. These observations place it +beyond a doubt that animal life is abundant in the ocean at depths +varying from 200 to 300 fathoms, that the forms at these great depths +differ greatly from those met with in ordinary dredgings, and that, at +all events in some cases, these animals are closely allied to, and would +seem to be directly descended from, the Fauna of the early tertiaries. + +"I think the latter result might almost have been anticipated; and, +probably, further investigation will largely add to this class of data, +and will give us an opportunity of testing our determinations of the +zoological position of some fossil types by an examination of the soft +parts of their recent representatives. The main cause of the destruction, +the migration, and the extreme modification of animal types, appear to be +change of climate, chiefly depending upon oscillations of the earth's +crust. These oscillations do not appear to have ranged, in the Northern +portion of the Northern Hemisphere, much beyond 1,000 feet since the +commencement of the Tertiary Epoch. The temperature of deep waters seems +to be constant for all latitudes at 39 deg.; so that an immense area of the +North Atlantic must have had its conditions unaffected by tertiary or +post-tertiary oscillations."[8] + +[Footnote 8: The Depths of the Sea, pp. 51-52.] + +As we shall see, the assumption that the temperature of the deep sea is +everywhere 39 deg. F. (4 deg. Cent.) is an error, which Dr. Wyville Thomson +adopted from eminent physical writers; but the general justice of the +reasoning is not affected by this circumstance, and Dr. Thomson's +expectation has been, to some extent, already verified. + +Thus besides _Globigerina_, there are eighteen species of deep-sea +_Foraminifera_ identical with species found in the chalk. Imbedded in the +chalky mud of the deep sea, in many localities, are innumerable cup- +shaped sponges, provided with six-rayed silicious spicula, so disposed +that the wall of the cup is formed of a lacework of flinty thread. Not +less abundant, in some parts of the chalk formation, are the fossils +known as _Ventriculites_, well described by Dr. Thomson as "elegant vases +or cups, with branching root-like bases, or groups of regularly or +irregularly spreading tubes delicately fretted on the surface with an +impressed network like the finest lace"; and he adds, "When we compare +such recent forms as _Aphrocallistes, Iphiteon, Holtenia_, and +_Askonema_, with certain series of the chalk _Ventriculites_, there +cannot be the slightest doubt that they belong to the same family--in +some cases to very nearly allied genera."[9] + +[Footnote 9: _The Depths of the Sea_, p. 484.] + +Professor Duncan finds "several corals from the coast of Portugal more +nearly allied to chalk forms than to any others." + +The Stalked Crinoids or Feather Stars, so abundant in ancient times, are +now exclusively confined to the deep sea, and the late explorations have +yielded forms of old affinity, the existence of which has hitherto been +unsuspected. The general character of the group of star fishes imbedded +in the white chalk is almost the same as in the modern Fauna of the deep +Atlantic. The sea urchins of the deep sea, while none of them are +specifically identical with any chalk form, belong to the same general +groups, and some closely approach extinct cretaceous genera. + +Taking these facts in conjunction with the positive evidence of the +existence, during the Cretaceous epoch, of a deep ocean where now lies +the dry land of central and southern Europe, northern Africa, and western +and southern Asia; and of the gradual diminution of this ocean during the +older tertiary epoch, until it is represented at the present day by such +teacupfuls as the Caspian, the Black Sea, and the Mediterranean; the +supposition of Dr. Thomson and Dr. Carpenter that what is now the deep +Atlantic, was the deep Atlantic (though merged in a vast easterly +extension) in the Cretaceous epoch, and that the _Globigerina_ mud has +been accumulating there from that time to this, seems to me to have a +great degree of probability. And I agree with Dr. Wyville Thomson against +Sir Charles Lyell (it takes two of us to have any chance against his +authority) in demurring to the assertion that "to talk of chalk having +been uninterruptedly formed in the Atlantic is as inadmissible in a +geographical as in a geological sense." + +If the word "chalk" is to be used as a stratigraphical term and +restricted to _Globigerina_ mud deposited during the Cretaceous epoch, of +course it is improper to call the precisely similar mud of more recent +date, chalk. If, on the other hand, it is to be used as a mineralogical +term, I do not see how the modern and the ancient chalks are to be +separated--and, looking at the matter geographically, I see no reason to +doubt that a boring rod driven from the surface of the mud which forms +the floor of the mid-Atlantic would pass through one continuous mass of +_Globigerina_ mud, first of modern, then of tertiary, and then of +mesozoic date; the "chalks" of different depths and ages being +distinguished merely by the different forms of other organisms associated +with the _Globigerinoe_. + +On the other hand, I think it must be admitted that a belief in the +continuity of the modern with the ancient chalk has nothing to do with +the proposition that we can, in any sense whatever, be said to be still +living in the Cretaceous epoch. When the _Challenger's_ trawl brings up +an _Ichthyosaurus_, along with a few living specimens of _Belemnites_ and +_Turrilites_, it may be admitted that she has come upon a cretaceous +"outlier." A geological period is characterized not only by the presence +of those creatures which lived in it, but by the absence of those which +have only come into existence later; and, however large a proportion of +true cretaceous forms may be discovered in the deep sea, the modern types +associated with them must be abolished before the Fauna, as a whole, +could, with any propriety, be termed Cretaceous. + + +I have now indicated some of the chief lines of Biological inquiry, in +which the _Challenger_ has special opportunities for doing good service, +and in following which she will be carrying out the work already +commenced by the _Lightning_ and _Porcupine_ in their cruises of 1868 and +subsequent years. + +But biology, in the long run, rests upon physics, and the first condition +for arriving at a sound theory of distribution in the deep sea, is the +precise ascertainment of the conditions of life; or, in other words, a +full knowledge of all those phenomena which are embraced under the head +of the Physical Geography of the Ocean. + +Excellent work has already been done in this direction, chiefly under the +superintendence of Dr. Carpenter, by the _Lightning_ and the +_Porcupine_,[10] and some data of fundamental importance to the physical +geography of the sea have been fixed beyond a doubt. + +[Footnote 10: _Proceedings of the Royal Society_, 1870 and 1872] + +Thus, though it is true that sea-water steadily contracts as it cools +down to its freezing point, instead of expanding before it reaches its +freezing point as fresh water does, the truth has been steadily ignored +by even the highest authorities in physical geography, and the erroneous +conclusions deduced from their erroneous premises have been widely +accepted as if they were ascertained facts. Of course, if sea-water, like +fresh water, were heaviest at a temperature of 39 deg. F. and got lighter as +it approached 32 deg. F., the water of the bottom of the deep sea could not +be colder than 39 deg.. But one of the first results of the careful +ascertainment of the temperature at different depths, by means of +thermometers specially contrived for the avoidance of the errors produced +by pressure, was the proof that, below 1000 fathoms in the Atlantic, down +to the greatest depths yet sounded, the water has a temperature always +lower than 38 deg. Fahr., whatever be the temperature of the water at the +surface. And that this low temperature of the deepest water is probably +the universal rule for the depths of the open ocean is shown, among +others, by Captain Chimmo's recent observations in the Indian ocean, +between Ceylon and Sumatra, where, the surface water ranging from 85 deg.-81 deg. +Fahr., the temperature at the bottom, at a depth of 2270 to 2656 fathoms, +was only from 34 deg. to 32 deg. Fahr. + +As the mean temperature of the superficial layer of the crust of the +earth may be taken at about 50 deg. Fahr., it follows that the bottom layer +of the deep sea in temperate and hot latitudes, is, on the average, much +colder than either of the bodies with which it is in contact; for the +temperature of the earth is constant, while that of the air rarely falls +so low as that of the bottom water in the latitudes in question; and even +when it does, has time to affect only a comparatively thin stratum of the +surface water before the return of warm weather. + +How does this apparently anomalous state of things come about? If we +suppose the globe to be covered with a universal ocean, it can hardly be +doubted that the cold of the regions towards the poles must tend to cause +the superficial water of those regions to contract and become +specifically heavier. Under these circumstances, it would have no +alternative but to descend and spread over the sea bottom, while its +place would be taken by warmer water drawn from the adjacent regions. +Thus, deep, cold, polar-equatorial currents, and superficial, warmer, +equatorial-polar currents, would be set up; and as the former would have +a less velocity of rotation from west to east than the regions towards +which they travel, they would not be due southerly or northerly currents, +but south-westerly in the northern hemisphere, and north-westerly in the +southern; while, by a parity of reasoning, the equatorial-polar warm +currents would be north-easterly in the northern hemisphere, and south- +easterly in the southern. Hence, as a north-easterly current has the same +direction as a south-westerly wind, the direction of the northern +equatorial-polar current in the extra-tropical part of its course would +pretty nearly coincide with that of the anti-trade winds. The freezing of +the surface of the polar sea would not interfere with the movement thus +set up. For, however bad a conductor of heat ice may be, the unfrozen +sea-water immediately in contact with the undersurface of the ice must +needs be colder than that further off; and hence will constantly tend to +descend through the subjacent warmer water. + +In this way, it would seem inevitable that the surface waters of the +northern and southern frigid zones must, sooner or later, find their way +to the bottom of the rest of the ocean; and there accumulate to a +thickness dependent on the rate at which they absorb heat from the crust +of the earth below, and from the surface water above. + +If this hypothesis be correct, it follows that, if any part of the ocean +in warm latitudes is shut off from the influence of the cold polar +underflow, the temperature of its deeps should be less cold than the +temperature of corresponding depths in the open sea. Now, in the +Mediterranean, Nature offers a remarkable experimental proof of just the +kind needed. It is a landlocked sea which runs nearly east and west, +between the twenty-ninth and forty-fifth parallels of north latitude. +Roughly speaking, the average temperature of the air over it is 75 deg. Fahr. +in July and 48 deg. in January. + +This great expanse of water is divided by the peninsula of Italy +(including Sicily), continuous with which is a submarine elevation +carrying less than 1,200 feet of water, which extends from Sicily to Cape +Bon in Africa, into two great pools--an eastern and a western. The +eastern pool rapidly deepens to more than 12,000 feet, and sends off to +the north its comparatively shallow branches, the Adriatic and the Aegean +Seas. The western pool is less deep, though it reaches some 10,000 feet. +And, just as the western end of the eastern pool communicates by a +shallow passage, not a sixth of its greatest depth, with the western +pool, so the western pool is separated from the Atlantic by a ridge which +runs between Capes Trafalgar and Spartel, on which there is hardly 1,000 +feet of water. All the water of the Mediterranean which lies deeper than +about 150 fathoms, therefore, is shut off from that of the Atlantic, and +there is no communication between the cold layer of the Atlantic (below +1,000 fathoms) and the Mediterranean. Under these circumstances, what is +the temperature of the Mediterranean? Everywhere below 600 feet it is +about 55 deg. Fahr.; and consequently, at its greatest depths, it is some 20 deg. +warmer than the corresponding depths of the Atlantic. + +It seems extremely difficult to account for this difference in any other +way, than by adopting the views so strongly and ably advocated by Dr. +Carpenter, that, in the existing distribution of land and water, such a +circulation of the water of the ocean does actually occur, as +theoretically must occur, in the universal ocean, with which we started. + +It is quite another question, however, whether this theoretic +circulation, true cause as it may be, is competent to give rise to such +movements of sea-water, in mass, as those currents, which have commonly +been regarded as northern extensions of the Gulf-stream. I shall not +venture to touch upon this complicated problem; but I may take occasion +to remark that the cause of a much simpler phenomenon--the stream of +Atlantic water which sets through the Straits of Gibraltar, eastward, at +the rate of two or three miles an hour or more, does not seem to be so +clearly made out as is desirable. + +The facts appear to be that the water of the Mediterranean is very +slightly denser than that of the Atlantic (1.0278 to 1.0265), and that +the deep water of the Mediterranean is slightly denser than that of the +surface; while the deep water of the Atlantic is, if anything, lighter +than that of the surface. Moreover, while a rapid superficial current is +setting in (always, save in exceptionally violent easterly winds) through +the Straits of Gibraltar, from the Atlantic to the Mediterranean, a deep +undercurrent (together with variable side currents) is setting out +through the Straits, from the Mediterranean to the Atlantic. + +Dr. Carpenter adopts, without hesitation, the view that the cause of this +indraught of Atlantic water is to be sought in the much more rapid +evaporation which takes place from the surface of the Mediterranean than +from that of the Atlantic; and thus, by lowering the level of the former, +gives rise to an indraught from the latter. + +But is there any sound foundation for the three assumptions involved +here? Firstly, that the evaporation from the Mediterranean, as a whole, +is much greater than that from the Atlantic under corresponding +parallels; secondly, that the rainfall over the Mediterranean makes up +for evaporation less than it does over the Atlantic; and thirdly, +supposing these two questions answered affirmatively: Are not these +sources of loss in the Mediterranean fully covered by the prodigious +quantity of fresh water which is poured into it by great rivers and +submarine springs? Consider that the water of the Ebro, the Rhine, the +Po, the Danube, the Don, the Dnieper, and the Nile, all flow directly or +indirectly into the Mediterranean; that the volume of fresh water which +they pour into it is so enormous that fresh water may sometimes be baled +up from the surface of the sea off the Delta of the Nile, while the land +is not yet in sight; that the water of the Black Sea is half fresh, and +that a current of three or four miles an hour constantly streams from it +Mediterraneanwards through the Bosphorus;--consider, in addition, that no +fewer than ten submarine springs of fresh water are known to burst up in +the Mediterranean, some of them so large that Admiral Smyth calls them +"subterranean rivers of amazing volume and force"; and it would seem, on +the face of the matter, that the sun must have enough to do to keep the +level of the Mediterranean down; and that, possibly, we may have to seek +for the cause of the small superiority in saline contents of the +Mediterranean water in some condition other than solar evaporation. + +Again, if the Gibraltar indraught is the effect of evaporation, why does +it go on in winter as well as in summer? + +All these are questions more easily asked than answered; but they must be +answered before we can accept the Gibraltar stream as an example of a +current produced by indraught with any comfort. + +The Mediterranean is not included in the _Challenger's_ route, but she +will visit one of the most promising and little explored of +hydrographical regions--the North Pacific, between Polynesia and the +Asiatic and American shores; and doubtless the store of observations upon +the currents of this region, which she will accumulate, when compared +with what we know of the North Atlantic, will throw a powerful light upon +the present obscurity of the Gulf-stream problem. + + + +III + + +ON SOME OF THE RESULTS OF THE EXPEDITION OF H.M.S. _CHALLLENGER_ + +[1875] + +In May, 1873, I drew attention[1] to the important problems connected +with the physics and natural history of the sea, to the solution of which +there was every reason to hope the cruise of H.M.S. _Challenger_ would +furnish important contributions. The expectation then expressed has not +been disappointed. Reports to the Admiralty, papers communicated to the +Royal Society, and large collections which have already been sent home, +have shown that the _Challenger's_ staff have made admirable use of their +great opportunities; and that, on the return of the expedition in 1874, +their performance will be fully up to the level of their promise. Indeed, +I am disposed to go so far as to say, that if nothing more came of the +_Challengers_ expedition than has hitherto been yielded by her +exploration of the nature of the sea bottom at great depths, a full +scientific equivalent of the trouble and expense of her equipment would +have been obtained. + +[Footnote 1: See the preceding Essay.] + +In order to justify this assertion, and yet, at the same time, not to +claim more for Professor Wyville Thomson and his colleagues than is their +due, I must give a brief history of the observations which have preceded +their exploration of this recondite field of research, and endeavour to +make clear what was the state of knowledge in December, 1872, and what +new facts have been added by the scientific staff of the _Challenger_. So +far as I have been able to discover, the first successful attempt to +bring up from great depths more of the sea bottom than would adhere to a +sounding-lead, was made by Sir John Ross, in the voyage to the Arctic +regions which he undertook in 1818. In the Appendix to the narrative of +that voyage, there will be found an account of a very ingenious apparatus +called "clams"--a sort of double scoop--of his own contrivance, which Sir +John Ross had made by the ship's armourer; and by which, being in +Baffin's Bay, in 72 deg. 30' N. and 77 deg. 15' W., he succeeded in bringing up +from 1,050 fathoms (or 6,300 feet), "several pounds" of a "fine green +mud," which formed the bottom of the sea in this region. Captain (now Sir +Edward) Sabine, who accompanied Sir John Ross on this cruise, says of +this mud that it was "soft and greenish, and that the lead sunk several +feet into it." A similar "fine green mud" was found to compose the sea +bottom in Davis Straits by Goodsir in 1845. Nothing is certainly known of +the exact nature of the mud thus obtained, but we shall see that the mud +of the bottom of the Antarctic seas is described in curiously similar +terms by Dr. Hooker, and there is no doubt as to the composition of this +deposit. + +In 1850, Captain Penny collected in Assistance Bay, in Kingston Bay, and +in Melville Bay, which lie between 73 deg. 45' and 74 deg. 40' N., specimens of +the residuum left by melted surface ice, and of the sea bottom in these +localities. Dr. Dickie, of Aberdeen, sent these materials to Ehrenberg, +who made out[2] that the residuum of the melted ice consisted for the +most part of the silicious cases of diatomaceous plants, and of the +silicious spicula of sponges; while, mixed with these, were a certain +number of the equally silicious skeletons of those low animal organisms, +which were termed _Polycistineoe_ by Ehrenberg, but are now known as +_Radiolaria_. + +[Footnote 2: _Ueber neue Anschauungen des kleinsten noerdlichen +Polarlebens_.--Monatsberichte d. K. Akad. Berlin, 1853.] + +In 1856, a very remarkable addition to our knowledge of the nature of the +sea bottom in high northern latitudes was made by Professor Bailey of +West Point. Lieutenant Brooke, of the United States Navy, who was +employed in surveying the Sea of Kamschatka, had succeeded in obtaining +specimens of the sea bottom from greater depths than any hitherto +reached, namely from 2,700 fathoms (16,200 feet) in 56 deg. 46' N., and 168 deg. +18' E.; and from 1,700 fathoms (10,200 feet) in 60 deg. 15' N. and 170 deg. 53' +E. On examining these microscopically, Professor Bailey found, as +Ehrenberg had done in the case of mud obtained on the opposite side of +the Arctic region, that the fine mud was made up of shells of +_Diatomacoe_, of spicula of sponges, and of _Radiolaria_, with a small +admixture of mineral matters, but without a trace of any calcareous +organisms. + +Still more complete information has been obtained concerning the nature +of the sea bottom in the cold zone around the south pole. Between the +years 1839 and 1843, Sir James Clark Ross executed his famous Antarctic +expedition, in the course of which he penetrated, at two widely distant +points of the Antarctic zone, into the high latitudes of the shores of +Victoria Land and of Graham's Land, and reached the parallel of 80 deg. S. +Sir James Ross was himself a naturalist of no mean acquirements, and Dr. +Hooker,[3] the present President of the Royal Society, accompanied him as +naturalist to the expedition, so that the observations upon the fauna and +flora of the Antarctic regions made during this cruise were sure to have +a peculiar value and importance, even had not the attention of the +voyagers been particularly directed to the importance of noting the +occurrence of the minutest forms of animal and vegetable life in the +ocean. + +[Footnote 3: Now Sir Joseph Hooker. 1894.] + +Among the scientific instructions for the voyage drawn up by a committee +of the Royal Society, however, there is a remarkable letter from Von +Humboldt to Lord Minto, then First Lord of the Admiralty, in which, among +other things, he dwells upon the significance of the researches into the +microscopic composition of rocks, and the discovery of the great share +which microscopic organisms take in the formation of the crust of the +earth at the present day, made by Ehrenberg in the years 1836-39. +Ehrenberg, in fact, had shown that the extensive beds of "rotten-stone" +or "Tripoli" which occur in various parts of the world, and notably at +Bilin in Bohemia, consisted of accumulations of the silicious cases and +skeletons of _Diatomaceoe_, sponges, and _Radiolaria_; he had proved that +similar deposits were being formed by _Diatomaceoe_, in the pools of the +Thiergarten in Berlin and elsewhere, and had pointed out that, if it were +commercially worth while, rotten-stone might be manufactured by a process +of diatom-culture. Observations conducted at Cuxhaven in 1839, had +revealed the existence, at the surface of the waters of the Baltic, of +living Diatoms and _Radiolaria_ of the same species as those which, in a +fossil state, constitute extensive rocks of tertiary age at Caltanisetta, +Zante, and Oran, on the shores of the Mediterranean. + +Moreover, in the fresh-water rotten-stone beds of Bilin, Ehrenberg had +traced out the metamorphosis, effected apparently by the action of +percolating water, of the primitively loose and friable deposit of +organized particles, in which the silex exists in the hydrated or soluble +condition. The silex, in fact, undergoes solution and slow redeposition, +until, in ultimate result, the excessively fine-grained sand, each +particle of which is a skeleton, becomes converted into a dense opaline +stone, with only here and there an indication of an organism. + +From the consideration of these facts, Ehrenberg, as early as the year +1839, had arrived at the conclusion that rocks, altogether similar to +those which constitute a large part of the crust of the earth, must be +forming, at the present day, at the bottom of the sea; and he threw out +the suggestion that even where no trace of organic structure is to be +found in the older rocks, it may have been lost by metamorphosis.[4] + +[Footnote 4: _Ueber die noch jetzt zahlreich lebende Thierarten der +Kreidebildung und den Organismus der Polythalamien. Abhandlungen der Koen. +Akad. der Wissenchaften._ 1839. _Berlin_. 1841. I am afraid that this +remarkable paper has been somewhat overlooked in the recent discussions +of the relation of ancient rocks to modern deposits.] + +The results of the Antarctic exploration, as stated by Dr. Hooker in the +"Botany of the Antarctic Voyage," and in a paper which he read before +the British Association in 1847, are of the greatest importance in +connection with these views, and they are so clearly stated in the former +work, which is somewhat inaccessible, that I make no apology for quoting +them at length-- + +"The waters and the ice of the South Polar Ocean were alike found to +abound with microscopic vegetables belonging to the order _Diatomaceoe_. +Though much too small to be discernible by the naked eye, they occurred +in such countless myriads as to stain the berg and the pack ice wherever +they were washed by the swell of the sea; and, when enclosed in the +congealing surface of the water, they imparted to the brash and pancake +ice a pale ochreous colour. In the open ocean, northward of the frozen +zone, this order, though no doubt almost universally present, generally +eludes the search of the naturalist; except when its species are +congregated amongst that mucous scum which is sometimes seen floating on +the waves, and of whose real nature we are ignorant; or when the coloured +contents of the marine animals who feed on these Algae are examined. To +the south, however, of the belt of ice which encircles the globe, between +the parallels of 50 deg. and 70 deg. S., and in the waters comprised between that +belt and the highest latitude ever attained by man, this vegetation is +very conspicuous, from the contrast between its colour and the white snow +and ice in which it is imbedded. Insomuch, that in the eightieth degree, +all the surface ice carried along by the currents, the sides of every +berg and the base of the great Victoria Barrier itself, within reach of +the swell, were tinged brown, as if the polar waters were charged with +oxide of iron. + +"As the majority of these plants consist of very simple vegetable cells, +enclosed in indestructible silex (as other Algae are in carbonate of +lime), it is obvious that the death and decomposition of such multitudes +must form sedimentary deposits, proportionate in their extent to the +length and exposure of the coast against which they are washed, in +thickness to the power of such agents as the winds, currents, and sea, +which sweep them more energetically to certain positions, and in purity, +to the depth of the water and nature of the bottom. Hence we detected +their remains along every icebound shore, in the depths of the adjacent +ocean, between 80 and 400 fathoms. Off Victoria Barrier (a perpendicular +wall of ice between one and two hundred feet above the level of the sea) +the bottom of the ocean was covered with a stratum of pure white or green +mud, composed principally of the silicious shells of the _Diatomaceoe_. +These, on being put into water, rendered it cloudy like milk, and took +many hours to subside. In the very deep water off Victoria and Graham's +Land, this mud was particularly pure and fine; but towards the shallow +shores there existed a greater or less admixture of disintegrated rock +and sand; so that the organic compounds of the bottom frequently bore but +a small proportion to the inorganic." ... + +"The universal existence of such an invisible vegetation as that of the +Antarctic Ocean, is a truly wonderful fact, and the more from its not +being accompanied by plants of a high order. During the years we spent +there, I had been accustomed to regard the phenomena of life as differing +totally from what obtains throughout all other latitudes, for everything +living appeared to be of animal origin. The ocean swarmed with +_Mollusca_, and particularly entomostracous _Crustacea_, small whales, +and porpoises; the sea abounded with penguins and seals, and the air with +birds; the animal kingdom was ever present, the larger creatures preying +on the smaller, and these again on smaller still; all seemed carnivorous. +The herbivorous were not recognised, because feeding on a microscopic +herbage, of whose true nature I had formed an erroneous impression. It +is, therefore, with no little satisfaction that I now class the +_Diatomaceoe_ with plants, probably maintaining in the South Polar Ocean +that balance between the vegetable and the animal kingdoms which prevails +over the surface of our globe. Nor is the sustenance and nutrition of the +animal kingdom the only function these minute productions may perform; +they may also be the purifiers of the vitiated atmosphere, and thus +execute in the Antarctic latitudes the office of our trees and grass turf +in the temperate regions, and the broad leaves of the palm, &c., in the +tropics." ... + +With respect to the distribution of the _Diatomaceoe_, Dr. Hooker +remarks:-- + +"There is probably no latitude between that of Spitzbergen and Victoria +Land, where some of the species of either country do not exist: Iceland, +Britain, the Mediterranean Sea, North and South America, and the South +Sea Islands, all possess Antarctic _Diatomaceoe_. The silicious coats of +species only known living in the waters of the South Polar Ocean, have, +during past ages, contributed to the formation of rocks; and thus they +outlive several successive creations of organized beings. The phonolite +stones of the Rhine, and the Tripoli stone, contain species identical +with what are now contributing to form a sedimentary deposit (and +perhaps, at some future period, a bed of rock) extending in one +continuous stratum for 400 measured miles. I allude to the shores of the +Victoria Barrier, along whose coast the soundings examined were +invariably charged with diatomaceous remains, constituting a bank which +stretches 200 miles north from the base of Victoria Barrier, while the +average depth of water above it is 300 fathoms, or 1,800 feet. Again, +some of the Antarctic species have been detected floating in the +atmosphere which overhangs the wide ocean between Africa and America. The +knowledge of this marvellous fact we owe to Mr. Darwin, who, when he was +at sea off the Cape de Verd Islands, collected an impalpable powder which +fell on Captain Fitzroy's ship. He transmitted this dust to Ehrenberg, +who ascertained it to consist of the silicious coats, chiefly of American +_Diatomaceoe_, which were being wafted through the upper region of the +air, when some meteorological phenomena checked them in their course and +deposited them on the ship and surface of the ocean. + +"The existence of the remains of many species of this order (and amongst +them some Antarctic ones) in the volcanic ashes, pumice, and scoriae of +active and extinct volcanoes (those of the Mediterranean Sea and +Ascension Island, for instance) is a fact bearing immediately upon the +present subject. Mount Erebus, a volcano 12,400 feet high, of the first +class in dimensions and energetic action, rises at once from the ocean in +the seventy-eighth degree of south latitude, and abreast of the +_Diatomaceoe_ bank, which reposes in part on its base. Hence it may not +appear preposterous to conclude that, as Vesuvius receives the waters of +the Mediterranean, with its fish, to eject them by its crater, so the +subterranean and subaqueous forces which maintain Mount Erebus in +activity may occasionally receive organic matter from the bank, and +disgorge it, together with those volcanic products, ashes and pumice. + +"Along the shores of Graham's Land and the South Shetland Islands, we +have a parallel combination of igneous and aqueous action, accompanied +with an equally copious supply of _Diatomaceoe_. In the Gulf of Erebus +and Terror, fifteen degrees north of Victoria Land, and placed on the +opposite side of the globe, the soundings were of a similar nature with +those of the Victoria Land and Barrier, and the sea and ice as full of +_Diatomaceoe_. This was not only proved by the deep sea lead, but by the +examination of bergs which, once stranded, had floated off and become +reversed, exposing an accumulation of white friable mud frozen to their +bases, which abounded with these vegetable remains." + +The _Challenger_ has explored the Antarctic seas in a region intermediate +between those examined by Sir James Ross's expedition; and the +observations made by Dr. Wyville Thomson and his colleagues in every +respect confirm those of Dr. Hooker:-- + +"On the 11th of February, lat. 60 deg. 52' S., long. 80 deg. 20' E., and March 3, +lat. 53 deg. 55' S., long. 108 deg. 35' E., the sounding instrument came up +filled with a very fine cream-coloured paste, which scarcely effervesced +with acid, and dried into a very light, impalpable, white powder. This, +when examined under the microscope, was found to consist almost entirely +of the frustules of Diatoms, some of them wonderfully perfect in all the +details of their ornament, and many of them broken up. The species of +Diatoms entering into this deposit have not yet been worked up, but they +appear to be referable chiefly to the genera _Fragillaria, Coscinodiscus, +Choetoceros, Asteromphalus_, and _Dictyocha_, with fragments of the +separated rods of a singular silicious organism, with which we were +unacquainted, and which made up a large proportion of the finer matter of +this deposit. Mixed with the Diatoms there were a few small +_Globigerinoe_, some of the tests and spicules of Radiolarians, and some +sand particles; but these foreign bodies were in too small proportion to +affect the formation as consisting practically of Diatoms alone. On the +4th of February, in lat. 52 deg., 29' S., long., 71 deg. 36" E., a little to the +north of the Heard Islands, the tow-net, dragging a few fathoms below the +surface, came up nearly filled with a pale yellow gelatinous mass. This +was found to consist entirely of Diatoms of the same species as those +found at the bottom. By far the most abundant was the little bundle of +silicious rods, fastened together loosely at one end, separating from one +another at the other end, and the whole bundle loosely twisted into a +spindle. The rods are hollow, and contain the characteristic endochrome +of the _Diatomaceoe_. Like the _Globigerina_ ooze, then, which it +succeeds to the southward in a band apparently of no great width, the +materials of this silicious deposit are derived entirely from the surface +and intermediate depths. It is somewhat singular that Diatoms did not +appear to be in such large numbers on the surface over the Diatom ooze as +they were a little further north. This may perhaps be accounted for by +our not having struck their belt of depth with the tow-net; or it is +possible that when we found it on the 11th of February the bottom deposit +was really shifted a little to the south by the warm current, the +excessively fine flocculent _debris_ of the Diatoms taking a certain time +to sink. The belt of Diatom ooze is certainly a little further to the +southward in long. 83 deg. E., in the path of the reflux of the Agulhas +current, than in long. 108 deg. E. + +"All along the edge of the ice-pack--everywhere, in fact, to the south of +the two stations--on the 11th of February on our southward voyage, and on +the 3rd of March on our return, we brought up fine sand and grayish mud, +with small pebbles of quartz and felspar, and small fragments of mica- +slate, chlorite-slate, clay-slate, gneiss, and granite. This deposit, I +have no doubt, was derived from the surface like the others, but in this +case by the melting of icebergs and the precipitation of foreign matter +contained in the ice. + +"We never saw any trace of gravel or sand, or any material necessarily +derived from land, on an iceberg. Several showed vertical or irregular +fissures filled with discoloured ice or snow; but, when looked at +closely, the discoloration proved usually to be very slight, and the +effect at a distance was usually due to the foreign material filling the +fissure reflecting light less perfectly than the general surface of the +berg. I conceive that the upper surface of one of these great tabular +southern icebergs, including by far the greater part of its bulk, and +culminating in the portion exposed above the surface of the sea, was +formed by the piling up of successive layers of snow during the period, +amounting perhaps to several centuries, during which the ice-cap was +slowly forcing itself over the low land and out to sea over a long extent +of gentle slope, until it reached a depth considerably above 200 fathoms, +when the lower specific weight of the ice caused an upward strain which +at length overcame the cohesion of the mass, and portions were rent off +and floated away. If this be the true history of the formation of these +icebergs, the absence of all land _debris_ in the portion exposed above +the surface of the sea is readily understood. If any such exist, it must +be confined to the lower part of the berg, to that part which has at one +time or other moved on the floor of the ice-cap. + +"The icebergs, when they are first dispersed, float in from 200 to 250 +fathoms. When, therefore, they have been drifted to latitudes of 65 deg. or +64 deg. S., the bottom of the berg just reaches the layer at which the +temperature of the water is distinctly rising, and it is rapidly melted, +and the mud and pebbles with which it is more or less charged are +precipitated. That this precipitation takes place all over the area where +the icebergs are breaking up, constantly, and to a considerable extent, +is evident from the fact of the soundings being entirely composed of such +deposits; for the Diatoms, _Globigerinoe_, and radiolarians are present +on the surface in large numbers; and unless the deposit from the ice were +abundant it would soon be covered and masked by a layer of the exuvia of +surface organisms." + +The observations which have been detailed leave no doubt that the +Antarctic sea bottom, from a little to the south of the fiftieth +parallel, as far as 80 deg. S., is being covered by a fine deposit of +silicious mud, more or less mixed, in some parts, with the ice-borne +_debris_ of polar lands and with the ejections of volcanoes. The +silicious particles which constitute this mud, are derived, in part, from +the diatomaceous plants and radiolarian animals which throng the surface, +and, in part, from the spicula of sponges which live at the bottom. The +evidence respecting the corresponding Arctic area is less complete, but +it is sufficient to justify the conclusion that an essentially similar +silicious cap is being formed around the northern pole. + +There is no doubt that the constituent particles of this mud may +agglomerate into a dense rock, such as that formed at Oran on the shores +of the Mediterranean, which is made up of similar materials. Moreover, in +the case of freshwater deposits of this kind it is certain that the +action of percolating water may convert the originally soft and friable, +fine-grained sandstone into a dense, semi-transparent opaline stone, the +silicious organized skeletons being dissolved, and the silex re-deposited +in an amorphous state. Whether such a metamorphosis as this occurs in +submarine deposits, as well as in those formed in fresh water, does not +appear; but there seems no reason to doubt that it may. And hence it may +not be hazardous to conclude that very ordinary metamorphic agencies may +convert these polar caps into a form of quartzite. + +In the great intermediate zone, occupying some 110 deg. of latitude, which +separates the circumpolar Arctic and Antarctic areas of silicious +deposit, the Diatoms and _Radiolaria_ of the surface water and the +sponges of the bottom do not die out, and, so far as some forms are +concerned, do not even appear to diminish in total number; though, on a +rough estimate, it would appear that the proportion of _Radiolaria_ to +Diatoms is much greater than in the colder seas. Nevertheless the +composition of the deep-sea mud of this intermediate zone is entirely +different from that of the circumpolar regions. + +The first exact information respecting the nature of this mud at depths +greater than 1,000 fathoms was given by Ehrenberg, in the account which +he published in the "Monatsberichte" of the Berlin Academy for the year +1853, of the soundings obtained by Lieut. Berryman, of the United States +Navy, in the North Atlantic, between Newfoundland and the Azores. + +Observations which confirm those of Ehrenberg in all essential respects +have been made by Professor Bailey, myself, Dr. Wallich, Dr. Carpenter, +and Professor Wyville Thomson, in their earlier cruises; and the +continuation of the _Globigerina_ ooze over the South Pacific has been +proved by the recent work of the _Challenger_, by which it is also shown, +for the first time, that, in passing from the equator to high southern +latitudes, the number and variety of the _Foraminifera_ diminishes, and +even the _Globigerinoe_ become dwarfed. And this result, it will be +observed, is in entire accordance with the fact already mentioned that, +in the sea of Kamschatka, the deep-sea mud was found by Bailey to contain +no calcareous organisms. + +Thus, in the whole of the "intermediate zone," the silicious deposit +which is being formed there, as elsewhere, by the accumulation of sponge- +spicula, _Radiolaria_, and Diatoms, is obscured and overpowered by the +immensely greater amount of calcareous sediment, which arises from the +aggregation of the skeletons of dead _Foraminifera_. The similarity of +the deposit, thus composed of a large percentage of carbonate of lime, +and a small percentage of silex, to chalk, regarded merely as a kind of +rock, which was first pointed out by Ehrenberg,[5] is now admitted on all +hands; nor can it be reasonably doubted, that ordinary metamorphic +agencies are competent to convert the "modern chalk" into hard limestone +or even into crystalline marble. + +[Footnote 5: The following passages in Ehrenberg's memoir on _The +Organisms in the Chalk which are still living_ (1839), are conclusive:-- + +"7. The dawning period of the existing living organic creation, if such a +period is distinguishable (which is doubtful), can only be supposed to +have existed on the other side of, and below, the chalk formation; and +thus, either the chalk, with its widespread and thick beds, must enter +into the series of newer formations; or some of the accepted four great +geological periods, the quaternary, tertiary, and secondary formations, +contain organisms which still live. It is more probable, in the +proportion of 3 to 1, that the transition or primary period is not +different, but that it is only more difficult to examine and understand, +by reason of the gradual and prolonged chemical decomposition and +metamorphosis of many of its organic constituents." + +"10. By the mass-forming _Infasoria_ and _Polythalamia_, secondary are +not distinguishable from tertiary formations; and, from what has been +said, it is possible that, at this very day, rock masses are forming in +the sea, and being raised by volcanic agencies, the constitution of +which, on the whole, is altogether similar to that of the chalk. The +chalk remains distinguishable by its organic remains as a formation, but +not as a kind of rock."] + +Ehrenberg appears to have taken it for granted that the _Globigerinoe_ +and other _Foraminifera_ which are found in the deep-sea mud, live at the +great depths in which their remains are found; and he supports this +opinion by producing evidence that the soft parts of these organisms are +preserved, and may be demonstrated by removing the calcareous matter with +dilute acids. In 1857, the evidence for and against this conclusion +appeared to me to be insufficient to warrant a positive conclusion one +way or the other, and I expressed myself in my report to the Admiralty on +Captain Dayman's soundings in the following terms:-- + +"When we consider the immense area over which this deposit is spread, the +depth at which its formation is going on, and its similarity to chalk, +and still more to such rocks as the marls of Caltanisetta, the question, +whence are all these organisms derived? becomes one of high scientific +interest. + +"Three answers have suggested themselves:-- + +"In accordance with the prevalent view of the limitation of life to +comparatively small depths, it is imagined either: 1, that these +organisms have drifted into their present position from shallower waters; +or 2, that they habitually live at the surface of the ocean, and only +fall down into their present position. + +"1. I conceive that the first supposition is negatived by the extremely +marked zoological peculiarity of the deep-sea fauna. + +"Had the _Globigerinoe_ been drifted into their present position from +shallow water, we should find a very large proportion of the +characteristic inhabitants of shallow waters mixed with them, and this +would the more certainly be the case, as the large _Globigerinoe_, so +abundant in the deep-sea soundings, are, in proportion to their size, +more solid and massive than almost any other _Foraminifera_. But the fact +is that the proportion of other _Foraminifera_ is exceedingly small, nor +have I found as yet, in the deep-sea deposits, any such matters as +fragments of molluscous shells, of _Echini_, &c., which abound in shallow +waters, and are quite as likely to be drifted as the heavy +_Globigerinoe_. Again, the relative proportions of young and fully formed +_Globigerinoe_ seem inconsistent with the notion that they have travelled +far. And it seems difficult to imagine why, had the deposit been +accumulated in this way, _Coscinodisci_ should so almost entirely +represent the _Diatomaceoe_. + +"2. The second hypothesis is far more feasible, and is strongly supported +by the fact that many _Polycistineoe [Radiolaria]_ and _Coscinodisci_ are +well known to live at the surface of the ocean. Mr. Macdonald, Assistant- +Surgeon of H.M.S. _Herald_, now in the South-Western Pacific, has lately +sent home some very valuable observations on living forms of this kind, +met with in the stomachs of oceanic mollusks, and therefore certainly +inhabitants of the superficial layer of the ocean. But it is a singular +circumstance that only one of the forms figured by Mr. Macdonald is at +all like a _Globigerina_, and there are some peculiarities about even +this which make me greatly doubt its affinity with that genus. The form, +indeed, is not unlike that of a _Globigerina_, but it is provided with +long radiating processes, of which I have never seen any trace in +_Globigerina_. Did they exist, they might explain what otherwise is a +great objection to this view, viz., how is it conceivable that the heavy +_Globigerina_ should maintain itself at the surface of the water? + +"If the organic bodies in the deep-sea soundings have neither been +drifted, nor have fallen from above, there remains but one alternative-- +they must have lived and died where they are. + +"Important objections, however, at once suggest themselves to this view. +How can animal life be conceived to exist under such conditions of light, +temperature, pressure, and aeration as must obtain at these vast depths? + +"To this one can only reply that we know for a certainty that even very +highly-organized animals do continue to live at a depth of 300 and 400 +fathoms, inasmuch as they have been dredged up thence; and that the +difference in the amount of light and heat at 400 and at 2,000 fathoms is +probably, so to speak, very far less than the difference in complexity of +organisation between these animals and the humbler _Protozoa_ and +_Protophyta_ of the deep-sea soundings. + +"I confess, though as yet far from regarding it proved that the +_Globigerinoe_ live at these depths, the balance of probabilities seems +to me to incline in that direction. And there is one circumstance which +weighs strongly in my mind. It may be taken as a law that any genus of +animals which is found far back in time is capable of living under a +great variety of circumstances as regards light, temperature, and +pressure. Now, the genus _Globigerina_ is abundantly represented in the +cretaceous epoch, and perhaps earlier. + +"I abstain, however, at present from drawing any positive conclusions, +preferring rather to await the result of more extended observations."[6] + +[Footnote 6: Appendix to Report on Deep-sea Soundings in the Atlantic +Ocean, by Lieut.-Commander Joseph Dayman. 1857.] + +Dr. Wallich, Professor Wyville Thomson, and Dr. Carpenter concluded that +the _Globigerinoe_ live at the bottom. Dr. Wallich writes in 1862--"By +sinking very fine gauze nets to considerable depths, I have repeatedly +satisfied myself that _Globigerina_ does not occur in the superficial +strata of the ocean."[7] Moreover, having obtained certain living star- +fish from a depth of 1,260 fathoms, and found their stomachs full of +"fresh-looking _Globigerinoe_" and their _debris_--he adduces this fact +in support of his belief that the _Globigerinoe_ live at the bottom. + +[Footnote 7: The _North Atlantic Sea-bed_, p. 137.] + +On the other hand, Mueller, Haeckel, Major Owen, Mr. Gwyn Jeffries, and +other observers, found that _Globigerinoe_, with the allied genera +_Orbulina_ and _Pulvinulina_, sometimes occur abundantly at the surface +of the sea, the shells of these pelagic forms being not unfrequently +provided with the long spines noticed by Macdonald; and in 1865 and 1866, +Major Owen more especially insisted on the importance of this fact. The +recent work of the _Challenger_ fully confirms Major Owen's statement. In +the paper recently published in the proceedings of the Royal Society,[8] +from which a quotation has already been made, Professor Wyville Thomson +says:-- + +"I had formed and expressed a very strong opinion on the matter. It +seemed to me that the evidence was conclusive that the _Foraminifera_ +which formed the _Globigerina_ ooze lived on the bottom, and that the +occurrence of individuals on the surface was accidental and exceptional; +but after going into the thing carefully, and considering the mass of +evidence which has been accumulated by Mr. Murray, I now admit that I was +in error; and I agree with him that it may be taken as proved that all +the materials of such deposits, with the exception, of course, of the +remains of animals which we now know to live at the bottom at all depths, +which occur in the deposit as foreign bodies, are derived from the +surface. + +[Footnote 8: "Preliminary Notes on the Nature of the Sea-bottom procured +by the soundings of H.M.S. _Challenger_ during her cruise in the Southern +Seas, in the early part of the year 1874."--_Proceedings of the Royal +Society_, Nov. 26, 1874.] + +"Mr. Murray has combined with a careful examination of the soundings a +constant use of the tow-net, usually at the surface, but also at depths +of from ten to one hundred fathoms; and he finds the closest relation to +exist between the surface fauna of any particular locality and the +deposit which is taking place at the bottom. In all seas, from the +equator to the polar ice, the tow-net contains _Globigerinoe_. They are +more abundant and of a larger size in warmer seas; several varieties, +attaining a large size and presenting marked varietal characters, are +found in the intertropical area of the Atlantic. In the latitude of +Kerguelen they are less numerous and smaller, while further south they +are still more dwarfed, and only one variety, the typical _Globigerina +bulloides_, is represented. The living _Globigerinoe_ from the tow-net +are singularly different in appearance from the dead shells we find at +the bottom. The shell is clear and transparent, and each of the pores +which penetrate it is surrounded by a raised crest, the crest round +adjacent pores coalescing into a roughly hexagonal network, so that the +pores appear to lie at the bottom of a hexagonal pit. At each angle of +this hexagon the crest gives off a delicate flexible calcareous spine, +which is sometimes four or five times the diameter of the shell in +length. The spines radiate symmetrically from the direction of the centre +of each chamber of the shell, and the sheaves of long transparent needles +crossing one another in different directions have a very beautiful +effect. The smaller inner chambers of the shell are entirely filled with +an orange-yellow granular sarcode; and the large terminal chamber usually +contains only a small irregular mass, or two or three small masses run +together, of the same yellow sarcode stuck against one side, the +remainder of the chamber being empty. No definite arrangement and no +approach to structure was observed in the sarcode, and no +differentiation, with the exception of round bright-yellow oil-globules, +very much like those found in some of the radiolarians, which are +scattered, apparently irregularly, in the sarcode. We never have been +able to detect, in any of the large number of _Globigerinoe_ which we +have examined, the least trace of pseudopodia, or any extension, in any +form, of the sarcode beyond the shell. + + * * * * * + +"In specimens taken with the tow-net the spines are very usually absent; +but that is probably on account of their extreme tenuity; they are broken +off by the slightest touch. In fresh examples from the surface, the dots +indicating the origin of the lost spines may almost always be made out +with a high power. There are never spines on the _Globigerinoe_ from the +bottom, even in the shallowest water." + + +There can now be no doubt, therefore, that _Globigerinoe_ live at the top +of the sea; but the question may still be raised whether they do not also +live at the bottom. In favour of this view, it has been urged that the +shells of the _Globigerinoe_ of the surface never possess such thick +walls as those which are fouled at the bottom, but I confess that I doubt +the accuracy of this statement. Again, the occurrence of minute +_Globigerinoe_ in all stages of development, at the greatest depths, is +brought forward as evidence that they live _in situ_. But considering the +extent to which the surface organisms are devoured, without +discrimination of young and old, by _Salpoe_ and the like, it is not +wonderful that shells of all ages should be among the rejectamenta. Nor +can the presence of the soft parts of the body in the shells which form +the _Globigerina_ ooze, and the fact, if it be one, that animals living +at the bottom use them as food, be considered as conclusive evidence that +the _Globigerinoe_ live at the bottom. Such as die at the surface, and +even many of those which are swallowed by other animals, may retain much +of their protoplasmic matter when they reach the depths at which the +temperature sinks to 34 deg. or 32 deg. Fahrenheit, where decomposition must +become exceedingly slow. + +Another consideration appears to me to be in favour of the view that the +_Globigerinoe_ and their allies are essentially surface animals. This is +the fact brought out by the _Challenger's_ work, that they have a +southern limit of distribution, which can hardly depend upon anything but +the temperature of the surface water. And it is to be remarked that this +southern limit occurs at a lower latitude in the Antarctic seas than it +does in the North Atlantic. According to Dr. Wallich ("The North Atlantic +Sea Bed," p. 157) _Globigerina_ is the prevailing form in the deposits +between the Faroe Islands and Iceland, and between Iceland and East +Greenland--or, in other words, in a region of the sea-bottom which lies +altogether north of the parallel of 60 deg. N.; while in the southern seas, +the _Globigerinoe_ become dwarfed and almost disappear between 50 deg. and +55 deg. S. On the other hand, in the sea of Kamschatka, the _Globigerinoe_ +have vanished in 56 deg. N., so that the persistence of the _Globigerina_ +ooze in high latitudes, in the North Atlantic, would seem to depend on +the northward curve of the isothermals peculiar to this region; and it is +difficult to understand how the formation of _Globigerina_ ooze can be +affected by this climatal peculiarity unless it be effected by surface +animals. + +Whatever may be the mode of life of the _Foraminifera_, to which the +calcareous element of the deep-sea "chalk" owes its existence, the fact +that it is the chief and most widely spread material of the sea-bottom in +the intermediate zone, throughout both the Atlantic and Pacific Oceans, +and the Indian Ocean, at depths from a few hundred to over two thousand +fathoms, is established. But it is not the only extensive deposit which +is now taking place. In 1853, Count Pourtales, an officer of the United +States Coast Survey, which has done so much for scientific hydrography, +observed, that the mud forming the sea-bottom at depths of one hundred +and fifty fathoms, in 31 deg. 32' N., 79 deg. 35' W., off the Coast of Florida, +was "a mixture, in about equal proportions, of _Globigerinoe_ and black +sand, probably greensand, as it makes a green mark when crushed on +paper." Professor Bailey, examining these grains microscopically, found +that they were casts of the interior cavities of _Foraminifera_, +consisting of a mineral known as _Glauconite_, which is a silicate of +iron and alumina. In these casts the minutest cavities and finest tubes +in the Foraminifer were sornetilnes reproduced in solid counterparts of +the glassy mineral, while the calcareous original had been entirely +dissolved away. + +Contemporaneously with these observations, the indefatigable Ehrenberg +had discovered that the "greensands" of the geologist were largely made +up of casts of a similar character, and proved the existence of +_Foraminifera_ at a very ancient geological epoch, by discovering such +casts in a greensand of Lower Silurian age, which occurs near St. +Petersburg. + +Subsequently, Messrs. Parker and Jones discovered similar casts in +process of formation, the original shell not having disappeared, in +specimens of the sea-bottom of the Australian seas, brought home by the +late Professor Jukes. And the _Challenger_ has observed a deposit of a +similar character in the course of the Agulhas current, near the Cape of +Good Hope, and in some other localities not yet defined. + +It would appear that this infiltration of _Foraminifera_ shells with +_Glauconite_ does not take place at great depths, but rather in what may +be termed a sublittoral region, ranging from a hundred to three hundred +fathoms. It cannot be ascribed to any local cause, for it takes place, +not only over large areas in the Gulf of Mexico and the Coast of Florida, +but in the South Atlantic and in the Pacific. But what are the conditions +which determine its occurrence, and whence the silex, the iron, and the +alumina (with perhaps potash and some other ingredients in small +quantity) of which the _Glauconite_ is composed, proceed, is a point on +which no light has yet been thrown. For the present we must be content +with the fact that, in certain areas of the "intermediate zone," +greensand is replacing and representing the primitively calcareo- +silicious ooze. + +The investigation of the deposits which are now being formed in the basin +of the Mediterranean, by the late Professor Edward Forbes, by Professor +Williamson and more recently by Dr. Carpenter, and a comparison of the +results thus obtained with what is known of the surface fauna, have +brought to light the remarkable fact, that while the surface and the +shallows abound with _Foraminifera_ and other calcareous shelled +organisms, the indications of life become scanty at depths beyond 500 or +600 fathoms, while almost all traces of it disappear at greater depths, +and at 1,000 to 2,000 fathoms the bottom is covered with a fine clay. + +Dr. Carpenter has discussed the significance of this remarkable fact, and +he is disposed to attribute the absence of life at great depths, partly +to the absence of any circulation of the water of the Mediterranean at +such depths, and partly to the exhaustion of the oxygen of the water by +the organic matter contained in the fine clay, which he conceives to be +formed by the finest particles of the mud brought down by the rivers +which flow into the Mediterranean. + +However this may be, the explanation thus offered of the presence of the +fine mud, and of the absence of organisms which ordinarily live at the +bottom, does not account for the absence of the skeletons of the +organisms which undoubtedly abound at the surface of the Mediterranean; +and it would seem to have no application to the remarkable fact +discovered by the _Challenger_, that in the open Atlantic and Pacific +Oceans, in the midst of the great intermediate zone, and thousands of +miles away from the embouchure of any river, the sea-bottom, at depths +approaching to and beyond 3,000 fathoms, no longer consists of +_Globigerina_ ooze, but of an excessively fine red clay. + +Professor Thomson gives the following account of this capital +discovery:-- + +"According to our present experience, the deposit of _Globigerina_ ooze +is limited to water of a certain depth, the extreme limit of the pure +characteristic formation being placed at a depth of somewhere about 2,250 +fathoms. Crossing from these shallower regions occupied by the ooze into +deeper soundings, we find, universally, that the calcareous formation +gradually passes into, and is finally replaced by, an extremely fine pure +clay, which occupies, speaking generally, all depths below 2,500 fathoms, +and consists almost entirely of a silicate of the red oxide of iron and +alumina. The transition is very slow, and extends over several hundred +fathoms of increasing depth; the shells gradually lose their sharpness of +outline, and assume a kind of 'rotten' look and a brownish colour, and +become more and more mixed with a fine amorphous red-brown powder, which +increases steadily in proportion until the lime has almost entirely +disappeared. This brown matter is in the finest possible state of +subdivision, so fine that when, after sifting it to separate any +organisms it might contain, we put it into jars to settle, it remained +for days in suspension, giving the water very much the appearance and +colour of chocolate. + +"In indicating the nature of the bottom on the charts, we came, from +experience and without any theoretical considerations, to use three terms +for soundings in deep water. Two of these, Gl. oz. and r. cl., were very +definite, and indicated strongly-marked formations, with apparently but +few characters in common; but we frequently got soundings which we could +not exactly call '_Globigerina_ ooze' or 'red clay,' and before we were +fully aware of the nature of these, we were in the habit of indicating +them as 'grey ooze' (gr. oz.) We now recognise the 'grey ooze' as an +intermediate stage between the _Globigerina_ ooze and the red clay; we +find that on one side, as it were, of an ideal line, the red clay +contains more and more of the material of the calcareous ooze, while on +the other, the ooze is mixed with an increasing proportion of 'red clay.' + +"Although we have met with the same phenomenon so frequently, that we +were at length able to predict the nature of the bottom from the depth of +the soundings with absolute certainty for the Atlantic and the Southern +Sea, we had, perhaps, the best opportunity of observing it in our first +section across the Atlantic, between Teneriffe and St. Thomas. The first +four stations on this section, at depths from 1,525 to 2,220 fathoms, +show _Globigerina_ ooze. From the last of these, which is about 300 miles +from Teneriffe, the depth gradually increases to 2,740 fathoms at 500, +and 2,950 fathoms at 750 miles from Teneriffe. The bottom in these two +soundings might have been called 'grey ooze,' for although its nature has +altered entirely from the _Globigerina_ ooze, the red clay into which it +is rapidly passing still contains a considerable admixture of carbonate +of lime. + +"The depth goes on increasing to a distance of 1,150 miles from +Teneriffe, when it reaches 3,150 fathoms; there the clay is pure and +smooth, and contains scarcely a trace of lime. From this great depth the +bottom gradually rises, and, with decreasing depth, the grey colour and +the calcareous composition of the ooze return. Three soundings in 2,050, +1,900, and 1,950 fathoms on the 'Dolphin Rise' gave highly characteristic +examples of the _Globigerina_ formation. Passing from the middle plateau +of the Atlantic into the western trough, with depths a little over 3,000 +fathoms, the red clay returned in all its purity; and our last sounding, +in 1,420 fathoms, before reaching Sombrero, restored the _Globigerina_ +ooze with its peculiar associated fauna. + +"This section shows also the wide extension and the vast geological +importance of the red clay formation. The total distance from Teneriffe +to Sombrero is about 2,700 miles. Proceeding from east to west, we have-- + +About 80 miles of volcanic mud and sand, + " 350 " _Globigerina_ ooze, + " 1,050 " red clay, + " 330 " _Globigerina_ ooze, + " 850 " red clay, + " 40 " _Globigerina_ ooze; + +giving a total of 1,900 miles of red clay to 720 miles of _Globigerina_ +ooze. + +"The nature and origin of this vast deposit of clay is a question of the +very greatest interest; and although I think there can be no doubt that +it is in the main solved, yet some matters of detail are still involved +in difficulty. My first impression was that it might be the most minutely +divided material, the ultimate sediment produced by the disintegration of +the land, by rivers and by the action of the sea on exposed coasts, and +held in suspension and distributed by ocean currents, and only making +itself manifest in places unoccupied by the _Globigerina_ ooze. Several +circumstances seemed, however, to negative this mode of origin. The +formation seemed too uniform: wherever we met with it, it had the same +character, and it only varied in composition in containing less or more +carbonate of lime. + +"Again, the were gradually becoming more and more convinced that all the +important elements of the _Globigerina_ ooze lived on the surface, and it +seemed evident that, so long as the condition on the surface remained the +same, no alteration of contour at the bottom could possibly prevent its +accumulation; and the surface conditions in the Mid-Atlantic were very +uniform, a moderate current of a very equal temperature passing +continuously over elevations and depressions, and everywhere yielding to +the tow-net the ooze-forming _Foraminifera_ in the same proportion. The +Mid-Atlantic swarms with pelagic _Mollusca_, and, in moderate depths, the +shells of these are constantly mixed with the _Globigerina_ ooze, +sometimes in number sufficient to make up a considerable portion of its +bulk. It is clear that these shells must fall in equal numbers upon the +red clay, but scarcely a trace of one of them is ever brought up by the +dredge on the red clay area. It might be possible to explain the absence +of shell-secreting animals living on the bottom, on the supposition that +the nature of the deposit was injurious to them; but then the idea of a +current sufficiently strong to sweep them away is negatived by the +extreme fineness of the sediment which is being laid down; the absence of +surface shells appears to be intelligible only on the supposition that +they are in some way removed. + +"We conclude, therefore, that the 'red clay' is not an additional +substance introduced from without, and occupying certain depressed +regions on account of some law regulating its deposition, but that it is +produced by the removal, by some means or other, over these areas, of the +carbonate of lime, which forms probably about 98 per cent. of the +material of the _Globigerina_ ooze. We can trace, indeed, every +successive stage in the removal of the carbonate of lime in descending +the slope of the ridge or plateau where the _Globigerina_ ooze is +forming, to the region of the clay. We find, first, that the shells of +pteropods and other surface _Mollusca_ which are constantly falling on +the bottom, are absent, or, if a few remain, they are brittle and yellow, +and evidently decaying rapidly. These shells of _Mollusca_ decompose more +easily and disappear sooner than the smaller, and apparently more +delicate, shells of rhizopods. The smaller _Foraminifera_ now give way, +and are found in lessening proportion to the larger; the coccoliths first +lose their thin outer border and then disappear; and the clubs of the +rhabdoliths get worn out of shape, and are last seen, under a high power, +as infinitely minute cylinders scattered over the field. The larger +_Foraminifera_ are attacked, and instead of being vividly white and +delicately sculptured, they become brown and worn, and finally they break +up, each according to its fashion; the chamber-walls of _Globigerina_ +fall into wedge-shaped pieces, which quickly disappear, and a thick rough +crust breaks away from the surface of _Orbulina_, leaving a thin inner +sphere, at first beautifully transparent, but soon becoming opaque and +crumbling away. + +"In the meantime the proportion of the amorphous 'red clay' to the +calcareous elements of all kinds increases, until the latter disappear, +with the exception of a few scattered shells of the larger +_Foraminifera_, which are still found even in the most characteristic +samples of the 'red clay.' + +"There seems to be no room left for doubt that the red clay is +essentially the insoluble residue, the _ash_, as it were, of the +calcareous organisms which form the _Globigerina_ ooze, after the +calcareous matter has been by some means removed. An ordinary mixture of +calcareous _Foraminifera_ with the shells of pteropods, forming a fair +sample of _Globigerina_ ooze from near St. Thomas, was carefully washed, +and subjected by Mr. Buchanan to the action of weak acid; and he found +that there remained after the carbonate of lime had been removed, about 1 +per cent. of a reddish mud, consisting of silica, alumina, and the red +oxide of iron. This experiment has been frequently repeated with +different samples of _Globigerina_ ooze, and always with the result that +a small proportion of a red sediment remains, which possesses all the +characters of the red clay." + + * * * * * + +"It seems evident from the observations here recorded, that _clay_, which +we have hitherto looked upon as essentially the product of the +disintegration of older rocks, may be, under certain circumstances, an +organic formation like chalk; that, as a matter of fact, an area on the +surface of the globe, which we have shown to be of vast extent, although +we are still far from having ascertained its limits, is being covered by +such a deposit at the present day. + +"It is impossible to avoid associating such a formation with the fine, +smooth, homogeneous clays and schists, poor in fossils, but showing worm- +tubes and tracks, and bunches of doubtful branching things, such as +Oldhamia, silicious sponges, and thin-shelled peculiar shrimps. Such +formations, more or less metamorphosed, are very familiar, especially to +the student of palaeozoic geology, and they often attain a vast thickness. +One is inclined, from the great resemblance between them in composition +and in the general character of the included fauna, to suspect that these +may be organic formations, like the modern red clay of the Atlantic and +Southern Sea, accumulations of the insoluble ashes of shelled creatures. + +"The dredging in the red clay on the 13th of March was usually rich. The +bag contained examples, those with calcareous shells rather stunted, of +most of the characteristic deep-water groups of the Southern Sea, +including _Umbellularia, Euplectella, Pterocrinus, Brisinga, Ophioglypha, +Pourtalesia_, and one or two _Mollusca_. This is, however, very rarely +the case. Generally the red clay is barren, or contains only a very small +number of forms." + +It must be admitted that it is very difficult, at present, to frame any +satisfactory explanation of the mode of origin of this singular deposit +of red clay. + +I cannot say that the theory put forward tentatively, and with much +reservation by Professor Thomson, that the calcareous matter is dissolved +out by the relatively fresh water of the deep currents from the Antarctic +regions, appears satisfactory to me. Nor do I see my way to the +acceptance of the suggestion of Dr. Carpenter, that the red clay is the +result of the decomposition of previously-formed greensand. At present +there is no evidence that greensand casts are ever formed at great +depths; nor has it been proved that _Glauconite_ is decomposable by the +agency of water and carbonic acid. + +I think it probable that we shall have to wait some time for a sufficient +explanation of the origin of the abyssal red clay, no less than for that +of the sublittoral greensand in the intermediate zone. But the importance +of the establishment of the fact that these various deposits are being +formed in the ocean, at the present day, remains the same; whether its +_rationale_ be understood or not. + +For, suppose the globe to be evenly covered with sea, to a depth say of a +thousand fathoms--then, whatever might be the mineral matter composing +the sea-bottom, little or no deposit would be formed upon it, the +abrading and denuding action of water, at such a depth, being exceedingly +slight. + +Next, imagine sponges, _Radiolaria, Foraminifera_, and diatomaceous +plants, such as those which now exist in the deep-sea, to be introduced: +they would be distributed according to the same laws as at present, the +sponges (and possibly some of the _Foraminifera_), covering the bottom, +while other _Foraminifera_, with the _Radiolaria_ and _Diatomacea_, would +increase and multiply in the surface waters. In accordance with the +existing state of things, the _Radiolaria_ and Diatoms would have a +universal distribution, the latter gathering most thickly in the polar +regions, while the _Foraminifera_ would be largely, if not exclusively, +confined to the intermediate zone; and, as a consequence of this +distribution, a bed of "chalk" would begin to form in the intermediate +zone, while caps of silicious rock would accumulate on the circumpolar +regions. + +Suppose, further, that a part of the intermediate area were raised to +within two or three hundred fathoms of the surface--for anything that we +know to the contrary, the change of level might determine the +substitution of greensand for the "chalk"; while, on the other hand, if +part of the same area were depressed to three thousand fathoms, that +change might determine the substitution of a different silicate of +alumina and iron--namely, clay--for the "chalk" that would otherwise be +formed. + +If the _Challenger_ hypothesis, that the red clay is the residue left by +dissolved _Foraminiferous_ skeletons, is correct, then all these deposits +alike would be directly, or indirectly, the product of living organisms. +But just as a silicious deposit may be metamorphosed into opal or +quartzite, and chalk into marble, so known metamorphic agencies may +metamorphose clay into schist, clay-slate, slate, gneiss, or even +granite. And thus, by the agency of the lowest and simplest of organisms, +our imaginary globe might be covered with strata, of all the chief kinds +of rock of which the known crust of the earth is composed, of indefinite +thickness and extent. + +The bearing of the conclusions which are now either established, or +highly probable, respecting the origin of silicious, calcareous, and +clayey rocks, and their metamorphic derivatives, upon the archaeology of +the earth, the elucidation of which is the ultimate object of the +geologist, is of no small importance. + +A hundred years ago the singular insight of Linnaeus enabled him to say +that "fossils are not the children but the parents of rocks,"[9] and the +whole effect of the discoveries made since his time has been to compile a +larger and larger commentary upon this text. It is, at present, a +perfectly tenable hypothesis that all siliceous and calcareous rocks are +either directly, or indirectly, derived from material which has, at one +time or other, formed part of the organized framework of living +organisms. Whether the same generalization may be extended to aluminous +rocks, depends upon the conclusion to be drawn from the facts respecting +the red clay areas brought to light by the _Challenger_. If we accept the +view taken by Wyville Thomson and his colleagues--that the red clay is +the residuum left after the calcareous matter of the _Globigerinoe_ ooze +has been dissolved away--then clay is as much a product of life as +limestone, and all known derivatives of clay may have formed part of +animal bodies. + +[Footnote 9: "Petrificata montium calcariorum non filii sed parentes +sunt, cum omnis calx oriatur ab animalibus."--_Systema Naturae_, Ed. xii., +t. iii., p. 154. It must be recollected that Linnaeus included silex, as +well as limestone, under the name of "calx," and that he would probably +have arranged Diatoms among animals, as part of "chaos." Ehrenberg quotes +another even more pithy passage, which I have not been able to find in +any edition of the _Systema_ accessible to me: "Sic lapides ab +animalibus, nec vice versa. Sic runes saxei non primaevi, sed temporis +filiae."] + +So long as the _Globigerinoe_;, actually collected at the surface, have +not been demonstrated to contain the elements of clay, the _Challenger_ +hypothesis, as I may term it, must be accepted with reserve and +provisionally, but, at present, I cannot but think that it is more +probable than any other suggestion which has been made. + +Accepting it provisionally, we arrive at the remarkable result that all +the chief known constituents of the crust of the earth may have formed +part of living bodies; that they may be the "ash" of protoplasm; that the +"_rupes saxei_" are not only _"temporis,"_ but "_vitae filiae_"; and, +consequently, that the time during which life has been active on the +globe may be indefinitely greater than the period, the commencement of +which is marked by the oldest known rocks, whether fossiliferous or +unfossiliferous. + +And thus we are led to see where the solution of a great problem and +apparent paradox of geology may lie. Satisfactory evidence now exists +that some animals in the existing world have been derived by a process of +gradual modification from pre-existing forms. It is undeniable, for +example, that the evidence in favour of the derivation of the horse from +the later tertiary _Hipparion_, and that of the _Hipparion_ from +_Anchitherium_, is as complete and cogent as such evidence can reasonably +be expected to be; and the further investigations into the history of the +tertiary mammalia are pushed, the greater is the accumulation of evidence +having the same tendency. So far from palaeontology lending no support to +the doctrine of evolution--as one sees constantly asserted--that +doctrine, if it had no other support, would have been irresistibly forced +upon us by the palaeontological discoveries of the last twenty years. + +If, however, the diverse forms of life which now exist have been produced +by the modification of previously-existing less divergent forms, the +recent and extinct species, taken as a whole, must fall into series which +must converge as we go back in time. Hence, if the period represented by +the rocks is greater than, or co-extensive with, that during which life +has existed, we ought, somewhere among the ancient formations, to arrive +at the point to which all these series converge, or from which, in other +words, they have diverged--the primitive undifferentiated protoplasmic +living things, whence the two great series of plants and animals have +taken their departure. + +But, as a matter of fact, the amount of convergence of series, in +relation to the time occupied by the deposition of geological formations, +is extraordinarily small. Of all animals the higher _Vertebrata_ are the +most complex; and among these the carnivores and hoofed animals +(_Ungulata_) are highly differentiated. Nevertheless, although the +different lines of modification of the _Carnivora_ and those of the +_Ungulata_, respectively, approach one another, and, although each group +is represented by less differentiated forms in the older tertiary rocks +than at the present day, the oldest tertiary rocks do not bring us near +the primitive form of either. If, in the same way, the convergence of the +varied forms of reptiles is measured against the time during which their +remains are preserved--which is represented by the whole of the tertiary +and mesozoic formations--the amount of that convergence is far smaller +than that of the lines of mammals between the present time and the +beginning of the tertiary epoch. And it is a broad fact that, the lower +we go in the scale of organization, the fewer signs are there of +convergence towards the primitive form from whence all must have +diverged, if evolution be a fact. Nevertheless, that it is a fact in some +cases, is proved, and I, for one, have not the courage to suppose that +the mode in which some species have taken their origin is different from +that in which the rest have originated. + +What, then, has become of all the marine animals which, on the hypothesis +of evolution, must have existed in myriads in those seas, wherein the +many thousand feet of Cambrian and Laurentian rocks now devoid, or almost +devoid, of any trace of life were deposited? + +Sir Charles Lyell long ago suggested that the azoic character of these +ancient formations might be due to the fact that they had undergone +extensive metamorphosis; and readers of the "Principles of Geology" will +be familiar with the ingenious manner in which he contrasts the theory of +the Gnome, who is acquainted only with the interior of the earth, with +those of ordinary philosophers, who know only its exterior. + +The metamorphism contemplated by the great modern champion of rational +geology is, mainly, that brought about by the exposure of rocks to +subterranean heat; and where no such heat could be shown to have +operated, his opponents assumed that no metamorphosis could have taken +place. But the formation of greensand, and still more that of the "red +clay" (if the _Challenger_ hypothesis be correct) affords an insight into +a new kind of metamorphosis--not igneous, but aqueous--by which the +primitive nature of a deposit may be masked as completely as it can be by +the agency of heat. And, as Wyville Thomson suggests, in the passage I +have quoted above (p. 17), it further enables us to assign a new cause +for the occurrence, so puzzling hitherto, of thousands of feet of +unfossiliferous fine-grained schists and slates, in the midst of +formations deposited in seas which certainly abounded in life. If the +great deposit of "red clay" now forming in the eastern valley of the +Atlantic were metamorphosed into slate and then upheaved, it would +constitute an "azoic" rock of enormous extent. And yet that rock is now +forming in the midst of a sea which swarms with living beings, the great +majority of which are provided with calcareous or silicious shells and +skeletons; and, therefore, are such as, up to this time, we should have +termed eminently preservable. + +Thus the discoveries made by the _Challenger_ expedition, like all recent +advances in our knowledge of the phenomena of biology, or of the changes +now being effected in the structure of the surface of the earth, are in +accordance with and lend strong support to, that doctrine of +Uniformitarianism, which, fifty years ago, was held only by a small +minority of English geologists--Lyell, Scrope, and De la Beche--but now, +thanks to the long-continued labours of the first two, and mainly to +those of Sir Charles Lyell, has gradually passed from the position of a +heresy to that of catholic doctrine. + +Applied within the limits of the time registered by the known fraction of +the crust of the earth, I believe that uniformitarianism is unassailable. +The evidence that, in the enormous lapse of time between the deposition +of the lowest Laurentian strata and the present day, the forces which +have modified the surface of the crust of the earth were different in +kind, or greater in the intensity of their action, than those which are +now occupied in the same work, has yet to be produced. Such evidence as +we possess all tends in the contrary direction, and is in favour of the +same slow and gradual changes occurring then as now. + +But this conclusion in nowise conflicts with the deductions of the +physicist from his no less clear and certain data. It may be certain that +this globe has cooled down from a condition in which life could not have +existed; it may be certain that, in so cooling, its contracting crust +must have undergone sudden convulsions, which were to our earthquakes as +an earthquake is to the vibration caused by the periodical eruption of a +Geyser; but in that case, the earth must, like other respectable parents, +have sowed her wild oats, and got through her turbulent youth, before we, +her children, have any knowledge of her. + +So far as the evidence afforded by the superficial crust of the earth +goes, the modern geologist can, _ex animo_, repeat the saying of Hutton, +"We find no vestige of a beginning--no prospect of an end." However, he +will add, with Hutton, "But in thus tracing back the natural operations +which have succeeded each other, and mark to us the course of time past, +we come to a period in which we cannot see any further." And if he seek +to peer into the darkness of this period, he will welcome the light +proffered by physics and mathematics. + + + +IV + + +YEAST + +[1871] + +It has been known, from time immemorial, that the sweet liquids which may +be obtained by expressing the juices of the fruits and stems of various +plants, or by steeping malted barley in hot water, or by mixing honey +with water--are liable to undergo a series of very singular changes, if +freely exposed to the air and left to themselves, in warm weather. +However clear and pellucid the liquid may have been when first prepared, +however carefully it may have been freed, by straining and filtration, +from even the finest visible impurities, it will not remain clear. After +a time it will become cloudy and turbid; little bubbles will be seen +rising to the surface, and their abundance will increase until the liquid +hisses as if it were simmering on the fire. By degrees, some of the solid +particles which produce the turbidity of the liquid collect at its +surface into a scum, which is blown up by the emerging air-bubbles into a +thick, foamy froth. Another moiety sinks to the bottom, and accumulates +as a muddy sediment, or "lees." + +When this action has continued, with more or less violence, for a certain +time, it gradually moderates. The evolution of bubbles slackens, and +finally comes to an end; scum and lees alike settle at the bottom, and +the fluid is once more clear and transparent. But it has acquired +properties of which no trace existed in the original liquid. Instead of +being a mere sweet fluid, mainly composed of sugar and water, the sugar +has more or less completely disappeared; and it has acquired that +peculiar smell and taste which we call "spirituous." Instead of being +devoid of any obvious effect upon the animal economy, it has become +possessed of a very wonderful influence on the nervous system; so that in +small doses it exhilarates, while in larger it stupefies, and may even +destroy life. + +Moreover, if the original fluid is put into a still, and heated +moderately, the first and last product of its distillation is simple +water; while, when the altered fluid is subjected to the same process, +the matter which is first condensed in the receiver is found to be a +clear, volatile substance, which is lighter than water, has a pungent +taste and smell, possesses the intoxicating powers of the fluid in an +eminent degree, and takes fire the moment it is brought in contact with a +flame. The Alchemists called this volatile liquid, which they obtained +from wine, "spirits of wine," just as they called hydrochloric acid +"spirits of salt," and as we, to this day, call refined turpentine +"spirits of turpentine." As the "spiritus," or breath, of a man was +thought to be the most refined and subtle part of him, the intelligent +essence of man was also conceived as a sort of breath, or spirit; and, by +analogy, the most refined essence of anything was called its "spirit." +And thus it has come about that we use the same word for the soul of man +and for a glass of gin. + +At the present day, however, we even more commonly use another name for +this peculiar liquid--namely, "alcohol," and its origin is not less +singular. The Dutch physician, Van Helmont, lived in the latter part of +the sixteenth and the beginning of the seventeenth century--in the +transition period between alchemy and chemistry--and was rather more +alchemist than chemist. Appended to his "Opera Omnia," published in 1707, +there is a very needful "Clavis ad obscuriorum sensum referendum," in +which the following passage occurs.-- + +"ALCOHOL.--Chymicis est liquor aut pulvis summe subtilisatus, vocabulo +Orientalibus quoque, cum primis Habessinis, familiari, quibus _cohol_ +speciatim pulverem impalpabilem ex antimonio pro oculis tingendis denotat +... Hodie autem, ob analogiam, quivis pulvis tenerior ut pulvis oculorum +cancri summe subtilisatus _alcohol_ audit, haud aliter ac spiritus +rectificatissimi _alcolisati_ dicuntur." + +Similarly, Robert Boyle speaks of a fine powder as "alcohol"; and, so +late as the middle of the last century, the English lexicographer, Nathan +Bailey, defines "alcohol" as "the pure substance of anything separated +from the more gross, a very fine and impalpable powder, or a very pure, +well-rectified spirit." But, by the time of the publication of +Lavoisier's "Traite Elementaire de Chimie," in 1789, the term "alcohol," +"alkohol," or "alkool" (for it is spelt in all three ways), which Van +Helmont had applied primarily to a fine powder, and only secondarily to +spirits of wine, had lost its primary meaning altogether; and, from the +end of the last century until now, it has, I believe, been used +exclusively as the denotation of spirits of wine, and bodies chemically +allied to that substance. + +The process which gives rise to alcohol in a saccharine fluid is known +tones as "fermentation"; a term based upon the apparent boiling up or +"effervescence" of the fermenting liquid, and of Latin origin. + +Our Teutonic cousins call the same process "gaehren," "gaesen," "goeschen," +and "gischen"; but, oddly enough, we do not seem to have retained their +verb or their substantive denoting the action itself, though we do use +names identical with, or plainly derived from, theirs for the scum and +lees. These are called, in Low German, "gaescht" and "gischt"; in Anglo- +Saxon, "gest," "gist," and "yst," whence our "yeast." Again, in Low +German and in Anglo-Saxon there is another name for yeast, having the +form "barm," or "beorm"; and, in the Midland Counties, "barm" is the name +by which yeast is still best known. In High German, there is a third name +for yeast, "hefe," which is not represented in English, so far as I know. + +All these words are said by philologers to be derived from roots +expressive of the intestine motion of a fermenting substance. Thus "hefe" +is derived from "heben," to raise; "barm" from "beren" or "baeren," to +bear up; "yeast," "yst," and "gist," have all to do with seething and +foam, with "yeasty" waves, and "gusty" breezes. + +The same reference to the swelling up of the fermenting substance is seen +in the Gallo-Latin terms "levure" and "leaven." + +It is highly creditable to the ingenuity of our ancestors that the +peculiar property of fermented liquids, in virtue of which they "make +glad the heart of man," seems to have been known in the remotest periods +of which we have any record. All savages take to alcoholic fluids as if +they were to the manner born. Our Vedic forefathers intoxicated +themselves with the juice of the "soma"; Noah, by a not unnatural +reaction against a superfluity of water, appears to have taken the +earliest practicable opportunity of qualifying that which he was obliged +to drink; and the ghosts of the ancient Egyptians were solaced by +pictures of banquets in which the wine-cup passes round, graven on the +walls of their tombs. A knowledge of the process of fermentation, +therefore, was in all probability possessed by the prehistoric +populations of the globe; and it must have become a matter of great +interest even to primaeval wine-bibbers to study the methods by which +fermented liquids could be surely manufactured. No doubt it was soon +discovered that the most certain, as well as the most expeditious, way of +making a sweet juice ferment was to add to it a little of the scum, or +lees, of another fermenting juice. And it can hardly be questioned that +this singular excitation of fermentation in one fluid, by a sort of +infection, or inoculation, of a little ferment taken from some other +fluid, together with the strange swelling, foaming, and hissing of the +fermented substance, must have always attracted attention from the more +thoughtful. Nevertheless, the commencement of the scientific analysis of +the phenomena dates from a period not earlier than the first half of the +seventeenth century. + +At this time, Van Helmont made a first step, by pointing out that the +peculiar hissing and bubbling of a fermented liquid is due, not to the +evolution of common air (which he, as the inventor of the term "gas," +calls "gas ventosum"), but to that of a peculiar kind of air such as is +occasionally met with in caves, mines, and wells, and which he calls "gas +sylvestre." + +But a century elapsed before the nature of this "gas sylvestre," or, as +it was afterwards called, "fixed air," was clearly determined, and it was +found to be identical with that deadly "choke-damp" by which the lives of +those who descend into old wells, or mines, or brewers' vats, are +sometimes suddenly ended; and with the poisonous aeriform fluid which is +produced by the combustion of charcoal, and now goes by the name of +carbonic acid gas. + +During the same time it gradually became evident that the presence of +sugar was essential to the production of alcohol and the evolution of +carbonic acid gas, which are the two great and conspicuous products of +fermentation. And finally, in 1787, the Italian chemist, Fabroni, made +the capital discovery that the yeast ferment, the presence of which is +necessary to fermentation, is what he termed a "vegeto-animal" substance; +that is, a body which gives of ammoniacal salts when it is burned, and +is, in other ways, similar to the gluten of plants and the albumen and +casein of animals. + +These discoveries prepared the way for the illustrious Frenchman, +Lavoisier, who first approached the problem of fermentation with a +complete conception of the nature of the work to be done. The words in +which he expresses this conception, in the treatise on elementary +chemistry to which reference has already been made, mark the year 1789 as +the commencement of a revolution of not less moment in the world of +science than that which simultaneously burst over the political world, +and soon engulfed Lavoisier himself in one of its mad eddies. + +"We may lay it down as an incontestable axiom that, in all the operations +of art and nature, nothing is created; an equal quantity of matter exists +both before, and after the experiment: the quality and quantity of the +elements remain precisely the same, and nothing takes place beyond +changes and modifications in the combinations of these elements. Upon +this principle the whole art of performing chemical experiments depends; +we must always suppose an exact equality between the elements of the body +examined and those of the products of its analysis. + +"Hence, since from must of grapes we procure alcohol and carbonic acid, I +have an undoubted right to suppose that must consists of carbonic acid +and alcohol. From these premisses we have two modes of ascertaining what +passes during vinous fermentation: either by determining the nature of, +and the elements which compose, the fermentable substances; or by +accurately examining the products resulting from fermentation; and it is +evident that the knowledge of either of these must lead to accurate +conclusions concerning the nature and composition of the other. From +these considerations it became necessary accurately to determine the +constituent elements of the fermentable substances; and for this purpose +I did not make use of the compound juices of fruits, the rigorous +analysis of which is perhaps impossible, but made choice of sugar, which +is easily analysed, and the nature of which I have already explained. +This substance is a true vegetable oxyd, with two bases, composed of +hydrogen and carbon, brought to the state of an oxyd by means of a +certain proportion of oxygen; and these three elements are combined in +such a way that a very slight force is sufficient to destroy the +equilibrium of their connection." + +After giving the details of his analysis of sugar and of the products of +fermentation, Lavoisier continues:-- + +"The effect of the vinous fermentation upon sugar is thus reduced to the +mere separation of its elements into two portions; one part is oxygenated +at the expense of the other, so as to form carbonic acid; while the other +part, being disoxygenated in favour of the latter, is converted into the +combustible substance called alkohol; therefore, if it were possible to +re-unite alkohol and carbonic acid together, we ought to form sugar."[1] + +[Footnote 1: _Elements of Chemistry_. By M. Lavoisier. Translated by +Robert Kerr. Second Edition, 1793 (pp. 186-196).] + +Thus Lavoisier thought he had demonstrated that the carbonic acid and the +alcohol which are produced by the process of fermentation, are equal in +weight to the sugar which disappears; but the application of the more +refined methods of modern chemistry to the investigation of the products +of fermentation by Pasteur, in 1860, proved that this is not exactly +true, and that there is a deficit of from 5 to 7 per cent of the sugar +which is not covered by the alcohol and carbonic acid evolved. The +greater part of this deficit is accounted for by the discovery of two +substances, glycerine and succinic acid, of the existence of which +Lavoisier was unaware, in the fermented liquid. But about 1-1/2 per cent. +still remains to be made good. According to Pasteur, it has been +appropriated by the yeast, but the fact that such appropriation takes +place cannot be said to be actually proved. + +However this may be, there can be no doubt that the constituent elements +of fully 98 per cent. of the sugar which has vanished during fermentation +have simply undergone rearrangement; like the soldiers of a brigade, who +at the word of command divide themselves into the independent regiments +to which they belong. The brigade is sugar, the regiments are carbonic +acid, succinic acid, alcohol, and glycerine. + +From the time of Fabroni, onwards, it has been admitted that the agent by +which this surprising rearrangement of the particles of the sugar is +effected is the yeast. But the first thoroughly conclusive evidence of +the necessity of yeast for the fermentation of sugar was furnished by +Appert, whose method of preserving perishable articles of food excited so +much attention in France at the beginning of this century. Gay-Lussac, in +his "Memoire sur la Fermentation,"[2] alludes to Appert's method of +preserving beer-wort unfermented for an indefinite time, by simply +boiling the wort and closing the vessel in which the boiling fluid is +contained, in such a way as thoroughly to exclude air; and he shows that, +if a little yeast be introduced into such wort, after it has cooled, the +wort at once begins to ferment, even though every precaution be taken to +exclude air. And this statement has since received full confirmation from +Pasteur. + +[Footnote 2: _Annales de Chimie_, 1810.] + +On the other hand, Schwann, Schroeder and Dutch, and Pasteur, have amply +proved that air may be allowed to have free access to beer-wort, without +exciting fermentation, if only efficient precautions are taken to prevent +the entry of particles of yeast along with the air. + +Thus, the truth that the fermentation of a simple solution of sugar in +water depends upon the presence of yeast, rests upon an unassailable +foundation; and the inquiry into the exact nature of the substance which +possesses such a wonderful chemical influence becomes profoundly +interesting. + +The first step towards the solution of this problem was made two +centuries ago by the patient and painstaking Dutch naturalist, +Leeuwenhoek, who in the year 1680 wrote thus:-- + +"Saepissime examinavi fermnentum cerevisiae, semperque hoc ex globulis per +materiam pellucidam fluitantibus, quarm cerevisiam esse censui, constare +observavi: vidi etiam evidentissime, unumquemque hujus fermenti globulum +denuo ex sex distinctis globulis constare, accurate eidem quantitate et +formae, cui globulis sanguinis nostri, respondentibus. + +"Verum talis mihi de horum origine et formatione conceptus formabam; +globulis nempe ex quibus farina Tritici, Hordei, Avenae, Fagotritici, se +constat aquae calore dissolvi et aquae commisceri; hac, vero aqua, quam +cerevisiam vocare licet, refrigescente, multos ex minimis particulis in +cerevisia coadunari, et hoc pacto efficere particulam sive globulum, quae +sexta pars est globuli faecis, et iterum sex ex hisce globulis +conjungi."[3] + +[Footnote 3: Leeuwenhoek, _Arcana Naturae Detecta._ Ed. Nov., 1721.] + +Thus Leeuwenhoek discovered that yeast consists of globules floating in a +fluid; but he thought that they were merely the starchy particles of the +grain from which the wort was made, rearranged. He discovered the fact +that yeast had a definite structure, but not the meaning of the fact. A +century and a half elapsed, and the investigation of yeast was +recommenced almost simultaneously by Cagniard de la Tour in France, and +by Schwann and Kuetzing in Germany. The French observer was the first to +publish his results; and the subject received at his hands and at those +of his colleague, the botanist Turpin, full and satisfactory +investigation. + +The main conclusions at which they arrived are these. The globular, or +oval, corpuscles which float so thickly in the yeast as to make it muddy, +though the largest are not more than one two-thousandth of an inch in +diameter, and the smallest may measure less than one seven-thousandth of +an inch, are living organisms. They multiply with great rapidity by +giving off minute buds, which soon attain the size of their parent, and +then either become detached or remain united, forming the compound +globules of which Leeuwenhoek speaks, though the constancy of their +arrangement in sixes existed only in the worthy Dutchman's imagination. + +It was very soon made out that these yeast organisms, to which Turpin +gave the name of _Torula cerevisioe_, were more nearly allied to the +lower Fungi than to anything else. Indeed Turpin, and subsequently +Berkeley and Hoffmann, believed that they had traced the development of +the _Torula_ into the well-known and very common mould--the _Penicillium +glaucum_. Other observers have not succeeded in verifying these +statements; and my own observations lead me to believe, that while the +connection between _Torula_ and the moulds is a very close one, it is of +a different nature from that which has been supposed. I have never been +able to trace the development of _Torula_ into a true mould; but it is +quite easy to prove that species of true mould, such as _Penicillium_, +when sown in an appropriate nidus, such as a solution of tartrate of +ammonia and yeast-ash, in water, with or without sugar, give rise to +_Toruloe_, similar in all respects to _T. cerevisioe_, except that they +are, on the average, smaller. Moreover, Bail has observed the development +of a _Torula_ larger than _T. cerevisioe_, from a _Mucor_, a mould allied +to _Penicillium_. + +It follows, therefore, that the _Toruloe_, or organisms of yeast, are +veritable plants; and conclusive experiments have proved that the power +which causes the rearrangement of the molecules of the sugar is +intimately connected with the life and growth of the plant. In fact, +whatever arrests the vital activity of the plant also prevents it from +exciting fermentation. + +Such being the facts with regard to the nature of yeast, and the changes +which it effects in sugar, how are they to be accounted for? Before +modern chemistry had come into existence, Stahl, stumbling, with the +stride of genius, upon the conception which lies at the bottom of all +modern views of the process, put forward the notion that the ferment, +being in a state of internal motion, communicated that motion to the +sugar, and thus caused its resolution into new substances. And Lavoisier, +as we have seen, adopts substantially the same view. But Fabroni, full of +the then novel conception of acids and bases and double decompositions, +propounded the hypothesis that sugar is an oxide with two bases, and the +ferment a carbonate with two bases; that the carbon of the ferment unites +with the oxygen of the sugar, and gives rise to carbonic acid; while the +sugar, uniting with the nitrogen of the ferment, produces a new substance +analogous to opium. This is decomposed by distillation, and gives rise to +alcohol. Next, in 1803, Thenard propounded a hypothesis which partakes +somewhat of the nature of both Stahl's and Fabroni's views. "I do not +believe with Lavoisier," he says, "that all the carbonic acid formed +proceeds from the sugar. How, in that case, could we conceive the action +of the ferment on it? I think that the first portions of the acid are due +to a combination of the carbon of the ferment with the oxygen of the +sugar, and that it is by carrying off a portion of oxygen from the last +that the ferment causes the fermentation to commence--the equilibrium +between the principles of the sugar being disturbed, they combine afresh +to form carbonic acid and alcohol." + +The three views here before us may be familiarly exemplified by supposing +the sugar to be a card-house. According to Stahl, the ferment is somebody +who knocks the table, and shakes the card-house down; according to +Fabroni, the ferment takes out some cards, but puts others in their +places; according to Thenard, the ferment simply takes a card out of the +bottom story, the result of which is that all the others fall. + +As chemistry advanced, facts came to light which put a new face upon +Stahl's hypothesis, and gave it a safer foundation than it previously +possessed. The general nature of these phenomena may be thus stated:--A +body, A, without giving to, or taking from, another body B, any material +particles, causes B to decompose into other substances, C, D, E, the sum +of the weights of which is equal to the weight of B, which decomposes. +Thus, bitter almonds contain two substances, amygdalin and synaptase, +which can be extracted, in a separate state, from the bitter almonds. The +amygdalin thus obtained, if dissolved in water, undergoes no change; but +if a little synaptase be added to the solution, the amygdalin splits up +into bitter almond oil, prussic acid, and a kind of sugar. + +A short time after Cagniard de la Tour discovered the yeast plant, +Liebig, struck with the similarity between this and other such processes +and the fermentation of sugar, put forward the hypothesis that yeast +contains a substance which acts upon sugar, as synaptase acts upon +amygdalin. And as the synaptase is certainly neither organized nor alive, +but a mere chemical substance, Liebig treated Cagniard de la Tour's +discovery with no small contempt, and, from that time to the present, has +steadily repudiated the notion that the decomposition of the sugar is, in +any sense, the result of the vital activity of the _Torula_. But, though +the notion that the _Torula_ is a creature which eats sugar and excretes +carbonic acid and alcohol, which is not unjustly ridiculed in the most +surprising paper that ever made its appearance in a grave scientific +journal,[4] may be untenable, the fact that the _Toruloe_ are alive, and +that yeast does not excite fermentation unless it contains living +_Toruloe_, stands fast. Moreover, of late years, the essential +participation of living organisms in fermentation other than the +alcoholic, has been clearly made out by Pasteur and other chemists. + +[Footnote 4: "Das entraethselte Geheimniss der geistigen Gaehrung +(Vorlaenfige briefliche Mittheilung)" is the title of an anonymous +contribution to Woehler and Liebig's _Annalen der Pharmacie_ for 1839, in +which a somewhat Rabelaisian imaginary description of the organisation of +the "yeast animals" and of the manner in which their functions are +performed, is given with a circumstantiality worthy of the author of +_Gulliver's Travels_. As a specimen of the writer's humour, his account +of what happens when fermentation comes to an end may suffice. "Sobald +naemlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich +gegenseitig selbst auf, was durch eine eigene Manipulation geschieht; +alles wird verdant bis auf die Eier, welche unveraendert durch den +Darmkanal hineingehen; man hat zuletzt wieder gaehrungsfaehige Hefe, +naemlich den Saamen der Thiere, der uebrig bleibt."] However, it may be +asked, is there any necessary opposition between the so-called "vital" +and the strictly physico-chemical views of fermentation? It is quite +possible that the living _Torula_ may excite fermentation in sugar, +because it constantly produces, as an essential part of its vital +manifestations, some substance which acts upon the sugar, just as the +synaptase acts upon the amygdalin. Or it may be, that, without the +formation of any such special substance, the physical condition of the +living tissue of the yeast plant is sufficient to effect that small +disturbance of the equilibrium of the particles of the sugar, which +Lavoisier thought sufficient to effect its decomposition. + +Platinum in a very fine state of division--known as platinum black, or +_noir de platine_--has the very singular property of causing alcohol to +change into acetic acid with great rapidity. The vinegar plant, which is +closely allied to the yeast plant, has a similar effect upon dilute +alcohol, causing it to absorb the oxygen of the air, and become converted +into vinegar; and Liebig's eminent opponent, Pasteur, who has done so +much for the theory and the practice of vinegar-making, himself suggests +that in this case-- + +"La cause du phenomene physique qui accompagne la vie de la plante reside +dans un etat physique propre, analogue a celui du noir de platine. Mais +il est essentiel de remarquer que cet etat physique de la plante est +etroitement lie avec la vie de cette plante."[5] + +[Footnote 5: _Etudes sur les Mycodermes_, Comptes-Rendus, liv., 1862.] + +Now, if the vinegar plant gives rise to the oxidation of alcohol, on +account of its merely physical constitution, it is at any rate possible +that the physical constitution of the yeast plant may exert a decomposing +influence on sugar. + +But, without presuming to discuss a question which leads us into the very +arcana of chemistry, the present state of speculation upon the _modus +operandi_ of the yeast plant in producing fermentation is represented, on +the one hand, by the Stahlian doctrine, supported by Liebig, according to +which the atoms of the sugar are shaken into new combinations either +directly by the _Toruloe_, or indirectly, by some substance formed by +them; and, on the other hand, by the Thenardian doctrine, supported by +Pasteur, according to which the yeast plant assimilates part of the +sugar, and, in so doing, disturbs the rest, and determines its resolution +into the products of fermentation. Perhaps the two views are not so much +opposed as they seem at first sight to be. + +But the interest which attaches to the influence of the yeast plants upon +the medium in which they live and grow does not arise solely from its +bearing upon the theory of fermentation. So long ago as 1838, Turpin +compared the _Toruloe_ to the ultimate elements of the tissues of animals +and plants--"Les organes elementaires de leurs tissus, comparables aux +petits vegetaux des levures ordinaires, sont aussi les decompositeurs des +substances qui les environnent." + +Almost at the same time, and, probably, equally guided by his study of +yeast, Schwann was engaged in those remarkable investigations into the +form and development of the ultimate structural elements of the tissues +of animals, which led him to recognise their fundamental identity with +the ultimate structural elements of vegetable organisms. + +The yeast plant is a mere sac, or "cell," containing a semi-fluid matter, +and Schwann's microscopic analysis resolved all living organisms, in the +long run, into an aggregation of such sacs or cells, variously modified; +and tended to show, that all, whatever their ultimate complication, begin +their existence in the condition of such simple cells. + +In his famous "Mikroskopische Untersuchungen" Schwann speaks of _Torula_ +as a "cell"; and, in a remarkable note to the passage in which he refers +to the yeast plant, Schwann says:-- + +"I have been unable to avoid mentioning fermentation, because it is the +most fully and exactly known operation of cells, and represents, in the +simplest fashion, the process which is repeated by every cell of the +living body." + +In other words, Schwann conceives that every cell of the living body +exerts an influence on the matter which surrounds and permeates it, +analogous to that which a _Torula_ exerts on the saccharine solution by +which it is bathed. A wonderfully suggestive thought, opening up views of +the nature of the chemical processes of the living body, which have +hardly yet received all the development of which they are capable. + +Kant defined the special peculiarity of the living body to be that the +parts exist for the sake of the whole and the whole for the sake of the +parts. But when Turpin and Schwann resolved the living body into an +aggregation of quasi-independent cells, each, like a _Torula_, leading +its own life and having its own laws of growth and development, the +aggregation being dominated and kept working towards a definite end only +by a certain harmony among these units, or by the superaddition of a +controlling apparatus, such as a nervous system, this conception ceased +to be tenable. The cell lives for its own sake, as well as for the sake +of the whole organism; and the cells which float in the blood, live at +its expense, and profoundly modify it, are almost as much independent +organisms as the _Toruloe_ which float in beer-wort. + +Schwann burdened his enunciation of the "cell theory" with two false +suppositions; the one, that the structures he called "nucleus"[6] and +"cell-wall" are essential to a cell; the other, that cells are usually +formed independently of other cells; but, in 1839, it was a vast and +clear gain to arrive at the conception, that the vital functions of all +the higher animals and plants are the resultant of the forces inherent in +the innumerable minute cells of which they are composed, and that each of +them is, itself, an equivalent of one of the lowest and simplest of +independent living beings--the _Torula_. + +[Footnote 6: Later investigations have thrown an entirely new light upon +the structure and the functional importance of the nucleus; and have +proved that Schwann did not over-estimate its importance. 1894.] + +From purely morphological investigations, Turpin and Schwann, as we have +seen, arrived at the notion of the fundamental unity of structure of +living beings. And, before long, the researches of chemists gradually led +up to the conception of the fundamental unity of their composition. + +So far back as 1803, Thenard pointed out, in most distinct terms, the +important fact that yeast contains a nitrogenous "animal" substance; and +that such a substance is contained in all ferments. Before him, Fabroni +and Fourcroy speak of the "vegeto-animal" matter of yeast. In 1844 Mulder +endeavoured to demonstrate that a peculiar substance, which he called +"protein," was essentially characteristic of living matter. + +In 1846, Payen writes:-- + +"Enfin, une loi sans exception me semble apparaitre dans les faits +nombreux que j'ai observes et conduire a envisager sous un nouveau jour +la vie vegetale; si je ne m'abuse, tout ce que dans les tissus vegetaux +la vue directe ou amplifiee nous permet de discerner sous la forme de +cellules et de vaisseaux, ne represente autre chose que les enveloppes +protectrices, les reservoirs et les conduits, a l'aide desquels les corps +animes qui les secretent et les faconnent, se logent, puisent et +charrient leurs aliments, deposent et isolent les matieres excretees." + +And again:-- + +"Afin de completer aujourd'hui l'enonce du fait general, je rappellerai +que les corps, doue des fonctions accomplies dans les tissus des plantes, +sont formes des elements qui constituent, en proportion peu variable, les +organismes animaux; qu'ainsi l'on est conduit a reconnaitre une immense +unite de composition elementaire dans tous les corps vivants de la +nature."[7] + +[Footnote 7: Mem. sur les Developpements des Vegetaux, &c.--_Mem. +Presentees_. ix. 1846.] + +In the year (1846) in which these remarkable passages were published, the +eminent German botanist, Von Mohl invented the word "protoplasm," as a +name for one portion of those nitrogenous contents of the cells of living +plants, the close chemical resemblance of which to the essential +constituents of living animals is so strongly indicated by Payen. And +through the twenty-five years that have passed, since the matter of life +was first called protoplasm, a host of investigators, among whom Cohn, +Max Schulze, and Kuehne must be named as leaders, have accumulated +evidence, morphological, physiological, and chemical, in favour of that +"immense unite de composition elementaire dans tous les corps vivants de +la nature," into which Payen had, so early, a clear insight. + +As far back as 1850, Cohn wrote, apparently without any knowledge of what +Payen had said before him:-- + +"The protoplasm of the botanist, and the contractile substance and +sarcode of the zoologist, must be, if not identical, yet in a high degree +analogous substances. Hence, from this point of view, the difference +between animals and plants consists in this; that, in the latter, the +contractile substance, as a primordial utricle, is enclosed within an +inert cellulose membrane, which permits it only to exhibit an internal +motion, expressed by the phenomena of rotation and circulation, while, in +the former, it is not so enclosed. The protoplasm in the form of the +primordial utricle is, as it were, the animal element in the plant, but +which is imprisoned, and only becomes free in the animal; or, to strip +off the metaphor which obscures simple thought, the energy of organic +vitality which is manifested in movement is especially exhibited by a +nitrogenous contractile substance, which in plants is limited and +fettered by an inert membrane, in animals not so."[8] + +[Footnote 8: Cohn, "Ueber Protococcus pluvialis," in the _Nova Acta_ for +1850.] + +In 1868, thinking that an untechnical statement of the views current +among the leaders of biological science might be interesting to the +general public, I gave a lecture embodying them in Edinburgh. Those who +have not made the mistake of attempting to approach biology, either by +the high _a priori_ road of mere philosophical speculation, or by the +mere low _a posteriori_ lane offered by the tube of a microscope, but +have taken the trouble to become acquainted with well-ascertained facts +and with their history, will not need to be told that in what I had to +say "as regards protoplasm" in my lecture "On the Physical Basis of Life" +(Vol. I. of these Essays, p. 130), there was nothing new; and, as I hope, +nothing that the present state of knowledge does not justify us in +believing to be true. Under these circumstances, my surprise may be +imagined, when I found, that the mere statement of facts and of views, +long familiar to me as part of the common scientific property of +Continental workers, raised a sort of storm in this country, not only by +exciting the wrath of unscientific persons whose pet prejudices they +seemed to touch, but by giving rise to quite superfluous explosions on +the part of some who should have been better informed. + +Dr. Stirling, for example, made my essay the subject of a special +critical lecture,[9] which I have read with much interest, though, I +confess, the meaning of much of it remains as dark to me as does the +"Secret of Hegel" after Dr. Stirling's elaborate revelation of it. Dr. +Stirling's method of dealing with the subject is peculiar. "Protoplasm" +is a question of history, so far as it is a name; of fact, so far as it +is a thing. Dr. Stirling, has not taken the trouble to refer to the +original authorities for his history, which is consequently a travesty; +and still less has he concerned himself with looking at the facts, but +contents himself with taking them also at second-hand. A most amusing +example of this fashion of dealing with scientific statements is +furnished by Dr. Stirling's remarks upon my account of the protoplasm of +the nettle hair. That account was drawn up from careful and often- +repeated observation of the facts. Dr. Stirling thinks he is offering a +valid criticism, when he says that my valued friend Professor Stricker +gives a somewhat different statement about protoplasm. But why in the +world did not this distinguished Hegelian look at a nettle hair for +himself, before venturing to speak about the matter at all? Why trouble +himself about what either Stricker or I say, when any tyro can see the +facts for himself, if he is provided with those not rare articles, a +nettle and a microscope? But I suppose this would have been +"_Aufklaerung_"--a recurrence to the base common-sense philosophy of the +eighteenth century, which liked to see before it believed, and to +understand before it criticised Dr. Stirling winds up his paper with the +following paragraph:-- + +[Footnote 9: Subsequently published under the title of "As regards +Protoplasm."] + +"In short, the whole position of Mr. Huxley, (1) that all organisms +consist alike of the same life-matter, (2) which life-matter is, for its +part, due only to chemistry, must be pronounced untenable--nor less +untenable (3) the materialism he would found on it." + +The paragraph contains three distinct assertions concerning my views, and +just the same number of utter misrepresentations of them. That which I +have numbered (1) turns on the ambiguity of the word "same," for a +discussion of which I would refer Dr. Stirling to a great hero of +"_Aufklaerung_" Archbishop Whately; statement number (2) is, in my +judgment, absurd, and certainly I have never said anything resembling it; +while, as to number (3), one great object of my essay was to show that +what is called "materialism" has no sound philosophical basis! + +As we have seen, the study of yeast has led investigators face to face +with problems of immense interest in pure chemistry, and in animal and +vegetable morphology. Its physiology is not less rich in subjects for +inquiry. Take, for example, the singular fact that yeast will increase +indefinitely when grown in the dark, in water containing only tartrate of +ammonia a small percentage of mineral salts and sugar. Out of these +materials the _Toruloe_ will manufacture nitrogenous protoplasm, +cellulose, and fatty matters, in any quantity, although they are wholly +deprived of those rays of the sun, the influence of which is essential to +the growth of ordinary plants. There has been a great deal of speculation +lately, as to how the living organisms buried beneath two or three +thousand fathoms of water, and therefore in all probability almost +deprived of light, live. If any of them possess the same powers as yeast +(and the same capacity for living without light is exhibited by some +other fungi) there would seem to be no difficulty about the matter. + +Of the pathological bearings of the study of yeast, and other such +organisms, I have spoken elsewhere. It is certain that, in some animals, +devastating epidemics are caused by fungi of low order--similar to those +of which _Torula_ is a sort of offshoot. It is certain that such diseases +are propagated by contagion and infection, in just the same way as +ordinary contagious and infectious diseases are propagated. Of course, it +does not follow from this, that all contagious and infectious diseases +are caused by organisms of as definite and independent a character as the +_Torula_; but, I think, it does follow that it is prudent and wise to +satisfy one's self in each particular case, that the "germ theory" cannot +and will not explain the facts, before having recourse to hypotheses +which have no equal support from analogy. + + + +V + + +ON THE FORMATION OF COAL + +[1870] + +The lumps of coal in a coal-scuttle very often have a roughly cubical +form. If one of them be picked out and examined with a little care, it +will be found that its six sides are not exactly alike. Two opposite +sides are comparatively smooth and shining, while the other four are much +rougher, and are marked by lines which run parallel with the smooth +sides. The coal readily splits along these lines, and the split surfaces +thus formed are parallel with the smooth faces. In other words, there is +a sort of rough and incomplete stratification in the lump of coal, as if +it were a book, the leaves of which had stuck together very closely. + +Sometimes the faces along which the coal splits are not smooth, but +exhibit a thin layer of dull, charred-looking substance, which is known +as "mineral charcoal." + +Occasionally one of the faces of a lump of coal will present impressions, +which are obviously those of the stem, or leaves, of a plant; but though +hard mineral masses of pyrites, and even fine mud, may occur here and +there, neither sand nor pebbles are met with. + +When the coal burns, the chief ultimate products of its combustion are +carbonic acid, water, and ammoniacal products, which escape up the +chimney; and a greater or less amount of residual earthy salts, which +take the form of ash. These products are, to a great extent, such as +would result from the burning of so much wood. + +These properties of coal may be made out without any very refined +appliances, but the microscope reveals something more. Black and opaque +as ordinary coal is, slices of it become transparent if they are cemented +in Canada balsam, and rubbed down very thin, in the ordinary way of +making thin sections of non-transparent bodies. But as the thin slices, +made in this way, are very apt to crack and break into fragments, it is +better to employ marine glue as the cementing material. By the use of +this substance, slices of considerable size and of extreme thinness and +transparency may be obtained.[1] + +[Footnote 1: My assistant in the Museum of Practical Geology, Mr. Newton, +invented this excellent method of obtaining thin slices of coal.] + +Now let us suppose two such slices to be prepared from our lump of coal-- +one parallel with the bedding, the other perpendicular to it; and let us +call the one the horizontal, and the other the vertical, section. The +horizontal section will present more or less rounded yellow patches and +streaks, scattered irregularly through the dark brown, or blackish, +ground substance; while the vertical section will exhibit mere elongated +bars and granules of the same yellow materials, disposed in lines which +correspond, roughly, with the general direction of the bedding of the +coal. + +This is the microscopic structure of an ordinary piece of coal. But if a +great series of coals, from different localities and seams, or even from +different parts of the same seam, be examined, this structure will be +found to vary in two directions. In the anthracitic, or stone-coals, +which burn like coke, the yellow matter diminishes, and the ground +substance becomes more predominant, blacker, and more opaque, until it +becomes impossible to grind a section thin enough to be translucent; +while, on the other hand, in such as the "Better-Bed" coal of the +neighbourhood of Bradford, which burns with much flame, the coal is of a +far lighter, colour and transparent sections are very easily obtained. In +the browner parts of this coal, sharp eyes will readily detect multitudes +of curious little coin-shaped bodies, of a yellowish brown colour, +embedded in the dark brown ground substance. On the average, these little +brown bodies may have a diameter of about one-twentieth of an inch. They +lie with their flat surfaces nearly parallel with the two smooth faces of +the block in which they are contained; and, on one side of each, there +may be discerned a figure, consisting of three straight linear marks, +which radiate from the centre of the disk, but do not quite reach its +circumference. In the horizontal section these disks are often converted +into more or less complete rings; while in the vertical sections they +appear like thick hoops, the sides of which have been pressed together. +The disks are, therefore, flattened bags; and favourable sections show +that the three-rayed marking is the expression of three clefts, which +penetrate one wall of the bag. + +The sides of the bags are sometimes closely approximated; but, when the +bags are less flattened, their cavities are, usually, filled with +numerous, irregularly rounded, hollow bodies, having the same kind of +wall as the large ones, but not more than one seven-hundredth of an inch +in diameter. + +In favourable specimens, again, almost the whole ground substance appears +to be made up of similar bodies--more or less carbonized or blackened-- +and, in these, there can be no doubt that, with the exception of patches +of mineral charcoal, here and there, the whole mass of the coal is made +up of an accumulation of the larger and of the smaller sacs. + +But, in one and the same slice, every transition can be observed from +this structure to that which has been described as characteristic of +ordinary coal. The latter appears to rise out of the former, by the +breaking-up and increasing carbonization of the larger and the smaller +sacs. And, in the anthracitic coals, this process appears to have gone to +such a length, as to destroy the original structure altogether, and to +replace it by a completely carbonized substance. + +Thus coal may be said, speaking broadly, to be composed of two +constituents: firstly, mineral charcoal; and, secondly, coal proper. The +nature of the mineral charcoal has long since been determined. Its +structure shows it to consist of the remains of the stems and leaves of +plants, reduced a little more than their carbon. Again, some of the coal +is made up of the crushed and flattened bark, or outer coat, of the stems +of plants, the inner wood of which has completely decayed away. But what +I may term the "saccular matter" of the coal, which, either in its +primary or in its degraded form constitutes by far the greater part of +all the bituminous coals I have examined, is certainly not mineral +charcoal; nor is its structure that of any stem or leaf. Hence its real +nature is at first by no means apparent, and has been the subject of much +discussion. + +The first person who threw any light upon the problem, as far as I have +been able to discover, was the well-known geologist, Professor Morris. It +is now thirty-four years since he carefully described and figured the +coin-shaped bodies, or larger sacs, as I have called them, in a note +appended to the famous paper "On the Coalbrookdale Coal-Field," published +at that time, by the present President of the Geological Society, Mr. +Prestwich. With much sagacity, Professor Morris divined the real nature +of these bodies, and boldly affirmed them to be the spore-cases of a +plant allied to the living club-mosses. + +But discovery sometimes makes a long halt; and it is only a few years +since Mr. Carruthers determined the plant (or rather one of the plants) +which produces these spore-cases, by finding the discoidal sacs still +adherent to the leaves of the fossilized cone which produced them. He +gave the name of _Flemingites gracilis_ to the plant of which the cones +form a part. The branches and stem of this plant are not yet certainly +known, but there is no sort of doubt that it was closely allied to the +_Lepidodendron_, the remains of which abound in the coal formation. The +_Lepidodendra_ were shrubs and trees which put one more in mind of an +_Araucaria_ than of any other familiar plant; and the ends of the +fruiting branches were terminated by cones, or catkins, somewhat like the +bodies so named in a fir, or a willow. These conical fruits, however, did +not produce seeds; but the leaves of which they were composed bore upon +their surfaces sacs full of spores or sporangia, such as those one sees +on the under surface of a bracken leaf. Now, it is these sporangia of the +Lepidodendroid plant _Flemingites_ which were identified by Mr. +Carruthers with the free sporangia described by Professor Morris, which +are the same as the large sacs of which I have spoken. And, more than +this, there is no doubt that the small sacs are the spores, which were +originally contained in the sporangia. + +The living club-mosses are, for the most part, insignificant and creeping +herbs, which, superficially, very closely resemble true mosses, and none +of them reach more than two or three feet in height. But, in their +essential structure, they very closely resemble the earliest +Lepidodendroid trees of the coal: their stems and leaves are similar; so +are their cones; and no less like are the sporangia and spores; while +even in their size, the spores of the _Lepidodendron_ and those of the +existing _Lycopodium_, or club-moss, very closely approach one another. + +Thus, the singular conclusion is forced upon us, that the greater and the +smaller sacs of the "Better-Bed" and other coals, in which the primitive +structure is well preserved, are simply the sporangia and spores of +certain plants, many of which were closely allied to the existing club- +mosses. And if, as I believe, it can be demonstrated that ordinary coal +is nothing but "saccular" coal which has undergone a certain amount of +that alteration which, if continued, would convert it into anthracite; +then, the conclusion is obvious, that the great mass of the coal we burn +is the result of the accumulation of the spores and spore-cases of +plants, other parts of which have furnished the carbonized stems and the +mineral charcoal, or have left their impressions on the surfaces of the +layer. + +Of the multitudinous speculations which, at various times, have been +entertained respecting the origin and mode of formation of coal, several +appear to be negatived, and put out of court, by the structural facts the +significance of which I have endeavoured to explain. These facts, for +example, do not permit us to suppose that coal is an accumulation of +peaty matter, as some have held. + +Again, the late Professor Quekett was one of the first observers who gave +a correct description of what I have termed the "saccular" structure of +coal; and, rightly perceiving that this structure was something quite +different from that of any known plant, he imagined that it proceeded +from some extinct vegetable organism which was peculiarly abundant +amongst the coal-forming plants. But this explanation is at once shown to +be untenable when the smaller and the larger sacs are proved to be spores +or sporangia. + +Some, once more, have imagined that coal was of submarine origin; and +though the notion is amply and easily refuted by other considerations, it +may be worth while to remark, that it is impossible to comprehend how a +mass of light and resinous spores should have reached the bottom of the +sea, or should have stopped in that position if they had got there. + +At the same time, it is proper to remark that I do not presume to suggest +that all coal must needs have the same structure; or that there may not +be coals in which the proportions of wood and spores, or spore-cases, are +very different from those which I have examined. All I repeat is, that +none of the coals which have come under my notice have enabled me to +observe such a difference. But, according to Principal Dawson, who has so +sedulously examined the fossil remains of plants in North America, it is +otherwise with the vast accumulations of coal in that country. + +"The true coal," says Dr. Dawson, "consists principally of the flattened +bark of Sigillarioid and other trees, intermixed with leaves of Ferns and +_Cordaites_, and other herbaceous _debris_, and with fragments of decayed +wood, constituting 'mineral charcoal,' all these materials having +manifestly alike grown and accumulated where we find them."[2] + +[Footnote 2: _Acadian Geology_, 2nd edition, p. 135.] + +When I had the pleasure of seeing Principal Dawson in London last summer, +I showed him my sections of coal, and begged him to re-examine some of +the American coals on his return to Canada, with an eye to the presence +of spores and sporangia, such as I was able to show him in our English +and Scotch coals. He has been good enough to do so; and in a letter dated +September 26th, 1870, he informs me that-- + +"Indications of spore-cases are rare, except in certain coarse shaly +coals and portions of coals, and in the roofs of the seams. The most +marked case I have yet met with is the shaly coal referred to as +containing _Sporangites_ in my paper on the conditions of accumulation of +coal ("Journal of the Geological Society," vol. xxii. pp. 115, 139, and +165). The purer coals certainly consist principally of cubical tissues +with some true woody matter, and the spore-cases, &c., are chiefly in the +coarse and shaly layers. This is my old doctrine in my two papers in the +"Journal of the Geological Society," and I see nothing to modify it. Your +observations, however, make it probable that the frequent _clear spots_ +in the cannels are spore-cases." + +Dr. Dawson's results are the more remarkable, as the numerous specimens +of British coal, from various localities, which I have examined, tell one +tale as to the predominance of the spore and sporangium element in their +composition; and as it is exactly in the finest and purest coals, such as +the "Better-Bed" coal of Lowmoor, that the spores and sporangia obviously +constitute almost the entire mass of the deposit. + +Coal, such as that which has been described, is always found in sheets, +or "seams," varying from a fraction of an inch to many feet in thickness, +enclosed in the substance of the earth at very various depths, between +beds of rock of different kinds. As a rule, every seam of coal rests upon +a thicker, or thinner, bed of clay, which is known as "under-clay." These +alternations of beds of coal, clay, and rock may be repeated many times, +and are known as the "coal-measures"; and in some regions, as in South +Wales and in Nova Scotia, the coal-measures attain a thickness of twelve +or fourteen thousand feet, and enclose eighty or a hundred seams of coal, +each with its under-clay, and separated from those above and below by +beds of sandstone and shale. + +The position of the beds which constitute the coal-measures is infinitely +diverse. Sometimes they are tilted up vertically, sometimes they are +horizontal, sometimes curved into great basins; sometimes they come to +the surface, sometimes they are covered up by thousands of feet of rock. +But, whatever their present position, there is abundant and conclusive +evidence that every under-clay was once a surface soil. Not only do +carbonized root-fibres frequently abound in these under-clays; but the +stools of trees, the trunks of which are broken off and confounded with +the bed of coal, have been repeatedly found passing into radiating roots, +still embedded in the under-clay. On many parts of the coast of England, +what are commonly known as "submarine forests" are to be seen at low +water. They consist, for the most part, of short stools of oak, beech, +and fir-trees, still fixed by their long roots in the bed of blue clay in +which they originally grew. If one of these submarine forest beds should +be gradually depressed and covered up by new deposits, it would present +just the same characters as an under-clay of the coal, if the +_Sigillaria_ and _Lepidodendron_ of the ancient world were substituted +for the oak, or the beech, of our own times. + +In a tropical forest, at the present day, the trunks of fallen trees, and +the stools of such trees as may have been broken by the violence of +storms, remain entire for but a short time. Contrary to what might be +expected, the dense wood of the tree decays, and suffers from the ravages +of insects, more swiftly than the bark. And the traveller, setting his +foot on a prostrate trunk, finds that it is a mere shell, which breaks +under his weight, and lands his foot amidst the insects, or the reptiles, +which have sought food or refuge within. + +The trees of the coal forests present parallel conditions. When the +fallen trunks which have entered into the composition of the bed of coal +are identifiable, they are mere double shells of bark, flattened together +in consequence of the destruction of the woody core; and Sir Charles +Lyell and Principal Dawson discovered, in the hollow stools of coal trees +of Nova Scotia, the remains of snails, millipedes, and salamander-like +creatures, embedded in a deposit of a different character from that which +surrounded the exterior of the trees. Thus, in endeavouring to comprehend +the formation of a seam of coal, we must try to picture to ourselves a +thick forest, formed for the most part of trees like gigantic club- +mosses, mares'-tails, and tree-ferns, with here and there some that had +more resemblance to our existing yews and fir-trees. We must suppose +that, as the seasons rolled by, the plants grew and developed their +spores and seeds; that they shed these in enormous quantities, which +accumulated on the ground beneath; and that, every now and then, they +added a dead frond or leaf; or, at longer intervals, a rotten branch, or +a dead trunk, to the mass. + +A certain proportion of the spores and seeds no doubt fulfilled their +obvious function, and, carried by the wind to unoccupied regions, +extended the limits of the forest; many might be washed away by rain into +streams, and be lost; but a large portion must have remained, to +accumulate like beech-mast, or acorns, beneath the trees of a modern +forest. + +But, in this case it may be asked, why does not our English coal consist +of stems and leaves to a much greater extent than it does? What is the +reason of the predominance of the spores and spore-cases in it? + +A ready answer to this question is afforded by the study of a living +full-grown club-moss. Shake it upon a piece of paper, and it emits a +cloud of fine dust, which falls over the paper, and is the well-known +Lycopodium powder. Now this powder used to be, and I believe still is, +employed for two objects which seem, at first sight, to have no +particular connection with one another. It is, or was, employed in making +lightning, and in making pills. The coats of the spores contain so much +resinous matter, that a pinch of Lycopodium powder, thrown through the +flame of a candle, burns with an instantaneous flash, which has long done +duty for lightning on the stage. And the same character makes it a +capital coating for pills; for the resinous powder prevents the drug from +being wetted by the saliva, and thus bars the nauseous flavour from the +sensitive papilla; of the tongue. + +But this resinous matter, which lies in the walls of the spores and +sporangia, is a substance not easily altered by air and water, and hence +tends to preserve these bodies, just as the bituminized cerecloth +preserves an Egyptian mummy; while, on the other hand, the merely woody +stem and leaves tend to rot, as fast as the wood of the mummy's coffin +has rotted. Thus the mixed heap of spores, leaves, and stems in the coal- +forest would be persistently searched by the long-continued action of air +and rain; the leaves and stems would gradually be reduced to little but +their carbon, or, in other words, to the condition of mineral charcoal in +which we find them; while the spores and sporangia remained as a +comparatively unaltered and compact residuum. + +There is, indeed, tolerably clear evidence that the coal must, under some +circumstances, have been converted into a substance hard enough to be +rolled into pebbles, while it yet lay at the surface of the earth; for in +some seams of coal, the courses of rivulets, which must have been living +water, while the stratum in which their remains are found was still at +the surface, have been observed to contain rolled pebbles of the very +coal through which the stream has cut its way. + +The structural facts are such as to leave no alternative but to adopt the +view of the origin of such coal as I have described, which has just been +stated; but, happily, the process is not without analogy at the present +day. I possess a specimen of what is called "white coal" from Australia. +It is an inflammable material, burning with a bright flame and having +much the consistence and appearance of oat-cake, which, I am informed +covers a considerable area. It consists, almost entirely, of a compacted +mass of spores and spore-cases. But the fine particles of blown sand +which are scattered through it, show that it must have accumulated, +subaerially, upon the surface of a soil covered by a forest of +cryptogamous plants, probably tree-ferns. + +As regards this important point of the subaerial region of coal, I am +glad to find myself in entire accordance with Principal Dawson, who bases +his conclusions upon other, but no less forcible, considerations. In a +passage, which is the continuation of that already cited, he writes:-- + +"(3) The microscopical structure and chemical composition of the beds of +cannel coal and earthy bitumen, and of the more highly bituminous and +carbonaceous shale, show them to have been of the nature of the fine +vegetable mud which accumulates in the ponds and shallow lakes of modern +swamps. When such tine vegetable sediment is mixed, as is often the case, +with clay, it becomes similar to the bituminous limestone and calcareo- +bituminous shales of the coal-measures. (4) A few of the under-clays, +which support beds of coal, are of the nature of the vegetable mud above +referred to; but the greater part are argillo-arenaceous in composition, +with little vegetable matter, and bleached by the drainage from them of +water containing the products of vegetable decay. They are, in short, +loamy or clay soils, and must have been sufficiently above water to admit +of drainage. The absence of sulphurets, and the occurrence of carbonate +of iron in connection with them, prove that, when they existed as soils, +rain-water, and not sea-water, percolated them. (5) The coal and the +fossil forests present many evidences of subaerial conditions. Most of +the erect and prostrate trees had become hollow shells of bark before +they were finally embedded, and their wood had broken into cubical pieces +of mineral charcoal. Land-snails and galley-worms (_Xylobius_) crept into +them, and they became dens, or traps, for reptiles. Large quantities of +mineral charcoal occur on the surface of all the large beds of coal. None +of these appearances could have been produced by subaqueous action. (6) +Though the roots of the _Sigillaria_ bear more resemblance to the +rhizomes of certain aquatic plants; yet, structurally, they are +absolutely identical with the roots of Cycads, which the stems also +resemble. Further, the _Sigillarioe_ grew on the same soils which +supported Conifers, _Lepidodendra_, _Cordaites_, and Ferns-plants which +could not have grown in water. Again, with the exception perhaps of some +_Pinnularioe_, and _Asterophyllites_, there is a remarkable absence from +the coal measures of any form of properly aquatic vegetation. (7) The +occurrence of marine, or brackish-water animals, in the roofs of coal- +beds, or even in the coal itself, affords no evidence of subaqueous +accumulation, since the same thing occurs in the case of modern submarine +forests. For these and other reasons, some of which are more fully stated +in the papers already referred to, while I admit that the areas of coal +accumulation were frequently submerged, I must maintain that the true +coal is a subaerial accumulation by vegetable growth on soils, wet and +swampy it is true, but not submerged." + +I am almost disposed to doubt whether it is necessary to make the +concession of "wet and swampy"; otherwise, there is nothing that I know +of to be said against this excellent conspectus of the reasons for +believing in the subaerial origin of coal. + +But the coal accumulated upon the area covered by one of the great +forests of the carboniferous epoch would in course of time, have been +wasted away by the small, but constant, wear and tear of rain and streams +had the land which supported it remained at the same level, or been +gradually raised to a greater elevation. And, no doubt, as much coal as +now exists has been destroyed, after its formation, in this way. What are +now known as coal districts owe their importance to the fact that they +were areas of slow depression, during a greater or less portion of the +carboniferous epoch; and that, in virtue of this circumstance, Mother +Earth was enabled to cover up her vegetable treasures, and preserve them +from destruction. + +Wherever a coal-field now exists, there must formerly have been free +access for a great river, or for a shallow sea, bearing sediment in the +shape of sand and mud. When the coal-forest area became slowly depressed, +the waters must have spread over it, and have deposited their burden upon +the surface of the bed of coal, in the form of layers, which are now +converted into shale, or sandstone. Then followed a period of rest, in +which the superincumbent shallow waters became completely filled up, and +finally replaced, by fine mud, which settled down into a new under-clay, +and furnished the soil for a fresh forest growth. This flourished, and +heaped up its spores and wood into coal, until the stage of slow +depression recommenced. And, in some localities, as I have mentioned, the +process was repeated until the first of the alternating beds had sunk to +near three miles below its original level at the surface of the earth. + +In reflecting on the statement, thus briefly made, of the main facts +connected with the origin of the coal formed during the carboniferous +epoch, two or three considerations suggest themselves. + +In the first place, the great phantom of geological time rises before the +student of this, as of all other, fragments of the history of our earth-- +springing irrepressibly out of the facts, like the Djin from the jar +which the fishermen so incautiously opened; and like the Djin again, +being vaporous, shifting, and indefinable, but unmistakably gigantic. +However modest the bases of one's calculation may be, the minimum of time +assignable to the coal period remains something stupendous. + +Principal Dawson is the last person likely to be guilty of exaggeration +in this matter, and it will be well to consider what he has to say about +it:-- + +"The rate of accumulation of coal was very slow. The climate of the +period, in the northern temperate zone, was of such a character that the +true conifers show rings of growth, not larger, nor much less distinct, +than those of many of their modern congeners. The _Sigillarioe_ and +_Calamites_ were not, as often supposed, composed wholly, or even +principally, of lax and soft tissues, or necessarily short-lived. The +former had, it is true, a very thick inner bark; but their dense woody +axis, their thick and nearly imperishable outer bark, and their scanty +and rigid foliage, would indicate no very rapid growth or decay. In the +case of the _Sigillarioe_, the variations in the leaf-scars in different +parts of the trunk, the intercalation of new ridges at the surface +representing that of new woody wedges in the axis, the transverse marks +left by the stages of upward growth, all indicate that several years must +have been required for the growth of stems of moderate size. The enormous +roots of these trees, and the condition of the coal-swamps, must have +exempted them from the danger of being overthrown by violence. They +probably fell in successive generations from natural decay; and making +every allowance for other materials, we may safely assert that every foot +of thickness of pure bituminous coal implies the quiet growth and fall of +at least fifty generations of _Sigillarioe_, and therefore an undisturbed +condition of forest growth enduring through many centuries. Further, +there is evidence that an immense amount of loose parenchymatous tissue, +and even of wood, perished by decay, and we do not know to what extent +even the most durable tissues may have disappeared in this way; so that, +in many coal-seams, we may have only a very small part of the vegetable +matter produced." + +Undoubtedly the force of these reflections is not diminished when the +bituminous coal, as in Britain, consists of accumulated spores and spore- +cases, rather than of stems. But, suppose we adopt Principal Dawson's +assumption, that one foot of coal represents fifty generations of coal +plants; and, further, make the moderate supposition that each generation +of coal plants took ten years to come to maturity--then, each foot- +thickness of coal represents five hundred years. The superimposed beds of +coal in one coal-field may amount to a thickness of fifty or sixty feet, +and therefore the coal alone, in that field, represents 500 x 50 = 25,000 +years. But the actual coal is but an insignificant portion of the total +deposit, which, as has been seen, may amount to between two and three +miles of vertical thickness. Suppose it be 12,000 feet--which is 240 +times the thickness of the actual coal--is there any reason why we should +believe it may not have taken 240 times as long to form? I know of none. +But, in this case, the time which the coal-field represents would be +25,000 x 240 = 6,000,000 years. As affording a definite chronology, of +course such calculations as these are of no value; but they have much use +in fixing one's attention upon a possible minimum. A man may be puzzled +if he is asked how long Rome took a-building; but he is proverbially safe +if he affirms it not to have been built in a day; and our geological +calculations are all, at present, pretty much on that footing. + +A second consideration which the study of the coal brings prominently +before the mind of any one who is familiar with palaeontology is, that the +coal Flora, viewed in relation to the enormous period of time which it +lasted, and to the still vaster period which has elapsed since it +flourished, underwent little change while it endured, and in its peculiar +characters, differs strangely little from that which at present exist. + +The same species of plants are to be met with throughout the whole +thickness of a coal-field, and the youngest are not sensibly different +from the oldest. But more than this. Notwithstanding that the +carboniferous period is separated from us by more than the whole time +represented by the secondary and tertiary formations, the great types of +vegetation were as distinct then as now. The structure of the modern +club-moss furnishes a complete explanation of the fossil remains of the +_Lepidodendra_, and the fronds of some of the ancient ferns are hard to +distinguish from existing ones. At the same time, it must be remembered, +that there is nowhere in the world, at present, any _forest_ which bears +more than a rough analogy with a coal-forest. The types may remain, but +the details of their form, their relative proportions, their associates, +are all altered. And the tree-fern forest of Tasmania, or New Zealand, +gives one only a faint and remote image of the vegetation of the ancient +world. + +Once more, an invariably-recurring lesson of geological history, at +whatever point its study is taken up: the lesson of the almost infinite +slowness of the modification of living forms. The lines of the pedigrees +of living things break off almost before they begin to converge. + +Finally, yet another curious consideration. Let us suppose that one of +the stupid, salamander-like Labyrinthodonts, which pottered, with much +belly and little leg, like Falstaff in his old age, among the coal- +forests, could have had thinking power enough in his small brain to +reflect upon the showers of spores which kept on falling through years +and centuries, while perhaps not one in ten million fulfilled its +apparent purpose, and reproduced the organism which gave it birth: surely +he might have been excused for moralizing upon the thoughtless and wanton +extravagance which Nature displayed in her operations. + +But we have the advantage over our shovel-headed predecessor--or possibly +ancestor--and can perceive that a certain vein of thrift runs through +this apparent prodigality. Nature is never in a hurry, and seems to have +had always before her eyes the adage, "Keep a thing long enough, and you +will find a use for it." She has kept her beds of coal many millions of +years without being able to find much use for them; she has sent them +down beneath the sea, and the sea-beasts could make nothing of them; she +has raised them up into dry land, and laid the black veins bare, and +still, for ages and ages, there was no living thing on the face of the +earth that could see any sort of value in them; and it was only the other +day, so to speak, that she turned a new creature out of her workshop, who +by degrees acquired sufficient wits to make a fire, and then to discover +that the black rock would burn. + +I suppose that nineteen hundred years ago, when Julius Caesar was good +enough to deal with Britain as we have dealt with New Zealand, the +primaeval Briton, blue with cold and woad, may have known that the strange +black stone, of which he found lumps here and there in his wanderings, +would burn, and so help to warm his body and cook his food. Saxon, Dane, +and Norman swarmed into the land. The English people grew into a powerful +nation, and Nature still waited for a full return of the capital she had +invested in the ancient club-mosses. The eighteenth century arrived, and +with it James Watt. The brain of that man was the spore out of which was +developed the modern steam-engine, and all the prodigious trees and +branches of modern industry which have grown out of this. But coal is as +much an essential condition of this growth and development as carbonic +acid is for that of a club-moss. Wanting coal, we could not have smelted +the iron needed to make our engines, nor have worked our engines when we +had got them. But take away the engines, and the great towns of Yorkshire +and Lancashire vanish like a dream. Manufactures give place to +agriculture and pasture, and not ten men can live where now ten thousand +are amply supported. + +Thus, all this abundant wealth of money and of vivid life is Nature's +interest upon her investment in club-mosses, and the like, so long ago. +But what becomes of the coal which is burnt in yielding this interest? +Heat comes out of it, light comes out of it; and if we could gather +together all that goes up the chimney, and all that remains in the grate +of a thoroughly-burnt coal-fire, we should find ourselves in possession +of a quantity of carbonic acid, water, ammonia, and mineral matters, +exactly equal in weight to the coal. But these are the very matters with +which Nature supplied the club-mosses which made the coal She is paid +back principal and interest at the same time; and she straightway invests +the carbonic acid, the water, and the ammonia in new forms of life, +feeding with them the plants that now live. Thrifty Nature! Surely no +prodigal, but most notable of housekeepers! + + + +VI + + +ON THE BORDER TERRITORY BETWEEN THE ANIMAL AND THE VEGETABLE KINGDOMS + +[1876] + +In the whole history of science there is nothing more remarkable than the +rapidity of the growth of biological knowledge within the last half- +century, and the extent of the modification which has thereby been +effected in some of the fundamental conceptions of the naturalist. + +In the second edition of the "Regne Animal," published in 1828, Cuvier +devotes a special section to the "Division of Organised Beings into +Animals and Vegetables," in which the question is treated with that +comprehensiveness of knowledge and clear critical judgment which +characterise his writings, and justify us in regarding them as +representative expressions of the most extensive, if not the profoundest, +knowledge of his time. He tells us that living beings have been +subdivided from the earliest times into _animated beings_, which possess +sense and motion, and _inanimated beings_, which are devoid of these +functions and simply vegetate. + +Although the roots of plants direct themselves towards moisture, and +their leaves towards air and light,--although the parts of some plants +exhibit oscillating movements without any perceptible cause, and the +leaves of others retract when touched,--yet none of these movements +justify the ascription to plants of perception or of will. From the +mobility of animals, Cuvier, with his characteristic partiality for +teleological reasoning, deduces the necessity of the existence in them of +an alimentary cavity, or reservoir of food, whence their nutrition may be +drawn by the vessels, which are a sort of internal roots; and, in the +presence of this alimentary cavity, he naturally sees the primary and the +most important distinction between animals and plants. + +Following out his teleological argument, Cuvier remarks that the +organisation of this cavity and its appurtenances must needs vary +according to the nature of the aliment, and the operations which it has +to undergo, before it can be converted into substances fitted for +absorption; while the atmosphere and the earth supply plants with juices +ready prepared, and which can be absorbed immediately. As the animal body +required to be independent of heat and of the atmosphere, there were no +means by which the motion of its fluids could be produced by internal +causes. Hence arose the second great distinctive character of animals, or +the circulatory system, which is less important than the digestive, since +it was unnecessary, and therefore is absent, in the more simple animals. + +Animals further needed muscles for locomotion and nerves for sensibility. +Hence, says Cuvier, it was necessary that the chemical composition of the +animal body should be more complicated than that of the plant; and it is +so, inasmuch as an additional substance, nitrogen, enters into it as an +essential element; while, in plants, nitrogen is only accidentally joined +with he three other fundamental constituents of organic beings--carbon, +hydrogen, and oxygen. Indeed, he afterwards affirms that nitrogen is +peculiar to animals; and herein he places the third distinction between +the animal and the plant. The soil and the atmosphere supply plants with +water, composed of hydrogen and oxygen; air, consisting of nitrogen and +oxygen; and carbonic acid, containing carbon and oxygen. They retain the +hydrogen and the carbon, exhale the superfluous oxygen, and absorb little +or no nitrogen. The essential character of vegetable life is the +exhalation of oxygen, which is effected through the agency of light. +Animals, on the contrary, derive their nourishment either directly or +indirectly from plants. They get rid of the superfluous hydrogen and +carbon, and accumulate nitrogen. The relations of plants and animals to +the atmosphere are therefore inverse. The plant withdraws water and +carbonic acid from the atmosphere, the animal contributes both to it. +Respiration--that is, the absorption of oxygen and the exhalation of +carbonic acid--is the specially animal function of animals, and +constitutes their fourth distinctive character. + +Thus wrote Cuvier in 1828. But, in the fourth and fifth decades of this +century, the greatest and most rapid revolution which biological science +has ever undergone was effected by the application of the modern +microscope to the investigation of organic structure; by the introduction +of exact and easily manageable methods of conducting the chemical +analysis of organic compounds; and finally, by the employment of +instruments of precision for the measurement of the physical forces which +are at work in the living economy. + +That the semi-fluid contents (which we now term protoplasm) of the cells +of certain plants, such as the _Charoe_ are in constant and regular +motion, was made out by Bonaventura Corti a century ago; but the fact, +important as it was, fell into oblivion, and had to be rediscovered by +Treviranus in 1807. Robert Brown noted the more complex motions of the +protoplasm in the cells of _Tradescantia_ in 1831; and now such movements +of the living substance of plants are well known to be some of the most +widely-prevalent phenomena of vegetable life. + +Agardh, and other of the botanists of Cuvier's generation, who occupied +themselves with the lower plants, had observed that, under particular +circumstances, the contents of the cells of certain water-weeds were set +free, and moved about with considerable velocity, and with all the +appearances of spontaneity, as locomotive bodies, which, from their +similarity to animals of simple organisation, were called "zoospores." +Even as late as 1845, however, a botanist of Schleiden's eminence dealt +very sceptically with these statements; and his scepticism was the more +justified, since Ehrenberg, in his elaborate and comprehensive work on +the _Infusoria_, had declared the greater number of what are now +recognised as locomotive plants to be animals. + +At the present day, innumerable plants and free plant cells are known to +pass the whole or part of their lives in an actively locomotive +condition, in no wise distinguishable from that of one of the simpler +animals; and, while in this condition, their movements are, to all +appearance, as spontaneous--as much the product of volition--as those of +such animals. + +Hence the teleological argument for Cuvier's first diagnostic character-- +the presence in animals of an alimentary cavity, or internal pocket, in +which they can carry about their nutriment--has broken down, so far, at +least, as his mode of stating it goes. And, with the advance of +microscopic anatomy, the universality of the fact itself among animals +has ceased to be predicable. Many animals of even complex structure, +which live parasitically within others, are wholly devoid of an +alimentary cavity. Their food is provided for them, not only ready +cooked, but ready digested, and the alimentary canal, become superfluous, +has disappeared. Again, the males of most Rotifers have no digestive +apparatus; as a German naturalist has remarked, they devote themselves +entirely to the "Minnedienst," and are to be reckoned among the few +realisations of the Byronic ideal of a lover. Finally, amidst the lowest +forms of animal life, the speck of gelatinous protoplasm, which +constitutes the whole body, has no permanent digestive cavity or mouth, +but takes in its food anywhere; and digests, so to speak, all over its +body. But although Cuvier's leading diagnosis of the animal from the +plant will not stand a strict test, it remains one of the most constant +of the distinctive characters of animals. And, if we substitute for the +possession of an alimentary cavity, the power of taking solid nutriment +into the body and there digesting it, the definition so changed will +cover all animals except certain parasites, and the few and exceptional +cases of non-parasitic animals which do not feed at all. On the other +hand, the definition thus amended will exclude all ordinary vegetable +organisms. + +Cuvier himself practically gives up his second distinctive mark when he +admits that it is wanting in the simpler animals. + +The third distinction is based on a completely erroneous conception of +the chemical differences and resemblances between the constituents of +animal and vegetable organisms, for which Cuvier is not responsible, as +it was current among contemporary chemists. It is now established that +nitrogen is as essential a constituent of vegetable as of animal living +matter; and that the latter is, chemically speaking, just as complicated +as the former. Starchy substances, cellulose and sugar, once supposed to +be exclusively confined to plants, are now known to be regular and normal +products of animals. Amylaceous and saccharine substances are largely +manufactured, even by the highest animals; cellulose is widespread as a +constituent of the skeletons of the lower animals; and it is probable +that amyloid substances are universally present in the animal organism, +though not in the precise form of starch. + +Moreover, although it remains true that there is an inverse relation +between the green plant in sunshine and the animal, in so far as, under +these circumstances, the green plant decomposes carbonic acid and exhales +oxygen, while the animal absorbs oxygen and exhales carbonic acid; yet, +the exact researches of the modern chemical investigators of the +physiological processes of plants have clearly demonstrated the fallacy +of attempting to draw any general distinction between animals and +vegetables on this ground. In fact, the difference vanishes with the +sunshine, even in the case of the green plant; which, in the dark, +absorbs oxygen and gives out carbonic acid like any animal.[1] On the +other hand, those plants, such as the fungi, which contain no chlorophyll +and are not green, are always, so far as respiration is concerned, in the +exact position of animals. They absorb oxygen and give out carbonic acid. + +[Footnote 1: There is every reason to believe that living plants, like +living animals, always respire, and, in respiring, absorb oxygen and give +off carbonic acid; but, that in green plants exposed to daylight or to +the electric light, the quantity of oxygen evolved in consequence of the +decomposition of carbonic acid by a special apparatus which green plants +possess exceeds that absorbed in the concurrent respiratory process.] + +Thus, by the progress of knowledge, Cuvier's fourth distinction between +the animal and the plant has been as completely invalidated as the third +and second; and even the first can be retained only in a modified form +and subject to exceptions. + +But has the advance of biology simply tended to break down old +distinctions, without establishing new ones? + +With a qualification, to be considered presently, the answer to this +question is undoubtedly in the affirmative. The famous researches of +Schwann and Schleiden in 1837 and the following years, founded the modern +science of histology, or that branch of anatomy which deals with the +ultimate visible structure of organisms, as revealed by the microscope; +and, from that day to this, the rapid improvement of methods of +investigation, and the energy of a host of accurate observers, have given +greater and greater breadth and firmness to Schwann's great +generalisation, that a fundamental unity of structure obtains in animals +and plants; and that, however diverse may be the fabrics, or _tissues_, +of which their bodies are composed, all these varied structures result +from the metamorphosis of morphological units (termed _cells_, in a more +general sense than that in which the word "cells" was at first employed), +which are not only similar in animals and in plants respectively, but +present a close resemblance, when those of animals and those of plants +are compared together. + +The contractility which is the fundamental condition of locomotion, has +not only been discovered to exist far more widely among plants than was +formerly imagined; but, in plants, the act of contraction has been found +to be accompanied, as Dr. Burdon Sanderson's interesting investigations +have shown, by a disturbance of the electrical state of the contractile +substance, comparable to that which was found by Du Bois Reymond to be a +concomitant of the activity of ordinary muscle in animals. + +Again, I know of no test by which the reaction of the leaves of the +Sundew and of other plants to stimuli, so fully and carefully studied by +Mr. Darwin, can be distinguished from those acts of contraction following +upon stimuli, which are called "reflex" in animals. + +On each lobe of the bilobed leaf of Venus's fly-trap (_Dionoea +muscipula_) are three delicate filaments which stand out at right angle +from the surface of the leaf. Touch one of them with the end of a fine +human hair and the lobes of the leaf instantly close together[2] in +virtue of an act of contraction of part of their substance, just as the +body of a snail contracts into its shell when one of its "horns" is +irritated. + +[Footnote 2: Darwin, _Insectivorous Plants_, p. 289.] + +The reflex action of the snail is the result of the presence of a nervous +system in the animal. A molecular change takes place in the nerve of the +tentacle, is propagated to the muscles by which the body is retracted, +and causing them to contract, the act of retraction is brought about. Of +course the similarity of the acts does not necessarily involve the +conclusion that the mechanism by which they are effected is the same; but +it suggests a suspicion of their identity which needs careful testing. + +The results of recent inquiries into the structure of the nervous system +of animals converge towards the conclusion that the nerve fibres, which +we have hitherto regarded as ultimate elements of nervous tissue, are not +such, but are simply the visible aggregations of vastly more attenuated +filaments, the diameter of which dwindles down to the limits of our +present microscopic vision, greatly as these have been extended by modern +improvements of the microscope; and that a nerve is, in its essence, +nothing but a linear tract of specially modified protoplasm between two +points of an organism--one of which is able to affect the other by means +of the communication so established. Hence, it is conceivable that even +the simplest living being may possess a nervous system. And the question +whether plants are provided with a nervous system or not, thus acquires a +new aspect, and presents the histologist and physiologist with a problem +of extreme difficulty, which must be attacked from a new point of view +and by the aid of methods which have yet to be invented. + +Thus it must be admitted that plants may be contractile and locomotive; +that, while locomotive, their movements may have as much appearance of +spontaneity as those of the lowest animals; and that many exhibit +actions, comparable to those which are brought about by the agency of a +nervous system in animals. And it must be allowed to be possible that +further research may reveal the existence of something comparable to a +nervous system in plants. So that I know not where we can hope to find +any absolute distinction between animals and plants, unless we return to +their mode of nutrition, and inquire whether certain differences of a +more occult character than those imagined to exist by Cuvier, and which +certainly hold good for the vast majority of animals and plants, are of +universal application. + +A bean may be supplied with water in which salts of ammonia and certain +other mineral salts are dissolved in due proportion; with atmospheric air +containing its ordinary minute dose of carbonic acid; and with nothing +else but sunlight and heat. Under these circumstances, unnatural as they +are, with proper management, the bean will thrust forth its radicle and +its plumule; the former will grow down into roots, the latter grow up +into the stem and leaves of a vigorous bean-plant; and this plant will, +in due time, flower and produce its crop of beans, just as if it were +grown in the garden or in the field. + +The weight of the nitrogenous protein compounds, of the oily, starchy, +saccharine and woody substances contained in the full-grown plant and its +seeds, will be vastly greater than the weight of the same substances +contained in the bean from which it sprang. But nothing has been supplied +to the bean save water, carbonic acid, ammonia, potash, lime, iron, and +the like, in combination with phosphoric, sulphuric, and other acids. +Neither protein, nor fat, nor starch, nor sugar, nor any substance in the +slightest degree resembling them, has formed part of the food of the +bean. But the weights of the carbon, hydrogen, oxygen, nitrogen, +phosphorus, sulphur, and other elementary bodies contained in the bean- +plant, and in the seeds which it produces, are exactly equivalent to the +weights of the same elements which have disappeared from the materials +supplied to the bean during its growth. Whence it follows that the bean +has taken in only the raw materials of its fabric, and has manufactured +them into bean-stuffs. + +The bean has been able to perform this great chemical feat by the help of +its green colouring matter, or chlorophyll; for it is only the green +parts of the plant which, under the influence of sunlight, have the +marvellous power of decomposing carbonic acid, setting free the oxygen +and laying hold of the carbon which it contains. In fact, the bean +obtains two of the absolutely indispensable elements of its substance +from two distinct sources; the watery solution, in which its roots are +plunged, contains nitrogen but no carbon; the air, to which the leaves +are exposed, contains carbon, but its nitrogen is in the state of a free +gas, in which condition the bean can make no use of it;[3] and the +chlorophyll[4] is the apparatus by which the carbon is extracted from the +atmospheric carbonic acid--the leaves being the chief laboratories in +which this operation is effected. + +[Footnote 3: I purposely assume that the air with which the bean is +supplied in the case stated contains no ammoniacal salts.] + +[Footnote 4: The recent researches of Pringsheim have raised a host of +questions as to the exact share taken by chlorophyll in the chemical +operations which are effected by the green parts of plants. It may be +that the chlorophyll is only a constant concomitant of the actual +deoxidising apparatus.] + +The great majority of conspicuous plants are, as everybody knows, green; +and this arises from the abundance of their chlorophyll. The few which +contain no chlorophyll and are colourless, are unable to extract the +carbon which they require from atmospheric carbonic acid, and lead a +parasitic existence upon other plants; but it by no means follows, often +as the statement has been repeated, that the manufacturing power of +plants depends on their chlorophyll, and its interaction with the rays of +the sun. On the contrary, it is easily demonstrated, as Pasteur first +proved, that the lowest fungi, devoid of chlorophyll, or of any +substitute for it, as they are, nevertheless possess the characteristic +manufacturing powers of plants in a very high degree. Only it is +necessary that they should be supplied with a different kind of raw +material; as they cannot extract carbon from carbonic acid, they must be +furnished with something else that contains carbon. Tartaric acid is such +a substance; and if a single spore of the commonest and most troublesome +of moulds--_Penicillium_--be sown in a saucerful of water, in which +tartrate of ammonia, with a small percentage of phosphates and sulphates +is contained, and kept warm, whether in the dark or exposed to light, it +will, in a short time, give rise to a thick crust of mould, which +contains many million times the weight of the original spore, in protein +compounds and cellulose. Thus we have a very wide basis of fact for the +generalisation that plants are essentially characterised by their +manufacturing capacity--by their power of working up mere mineral matters +into complex organic compounds. + +Contrariwise, there is a no less wide foundation for the generalisation +that animals, as Cuvier puts it, depend directly or indirectly upon +plants for the materials of their bodies; that is, either they are +herbivorous, or they eat other animals which are herbivorous. + +But for what constituents of their bodies are animals thus dependent upon +plants? Certainly not for their horny matter; nor for chondrin, the +proximate chemical element of cartilage; nor for gelatine; nor for +syntonin, the constituent of muscle; nor for their nervous or biliary +substances; nor for their amyloid matters; nor, necessarily, for their +fats. + +It can be experimentally demonstrated that animals can make these for +themselves. But that which they cannot make, but must, in all known +cases, obtain directly or indirectly from plants, is the peculiar +nitrogenous matter, protein. Thus the plant is the ideal _proletaire_ of +the living world, the worker who produces; the animal, the ideal +aristocrat, who mostly occupies himself in consuming, after the manner of +that noble representative of the line of Zaehdarm, whose epitaph is +written in "Sartor Resartus." + +Here is our last hope of finding a sharp line of demarcation between +plants and animals; for, as I have already hinted, there is a border +territory between the two kingdoms, a sort of no-man's-land, the +inhabitants of which certainly cannot be discriminated and brought to +their proper allegiance in any other way. + +Some months ago, Professor Tyndall asked me to examine a drop of infusion +of hay, placed under an excellent and powerful microscope, and to tell +him what I thought some organisms visible in it were. I looked and +observed, in the first place, multitudes of _Bacteria_ moving about with +their ordinary intermittent spasmodic wriggles. As to the vegetable +nature of these there is now no doubt. Not only does the close +resemblance of the _Bacteria_ to unquestionable plants, such as the +_Oscillatorioe_ and the lower forms of _Fungi_, justify this conclusion, +but the manufacturing test settles the question at once. It is only +needful to add a minute drop of fluid containing _Bacteria_, to water in +which tartrate, phosphate, and sulphate of ammonia are dissolved; and, in +a very short space of time, the clear fluid becomes milky by reason of +their prodigious multiplication, which, of course, implies the +manufacture of living Bacterium-stuff out of these merely saline matters. + +But other active organisms, very much larger than the _Bacteria_, +attaining in fact the comparatively gigantic dimensions of 1/3000 of an +inch or more, incessantly crossed the field of view. Each of these had a +body shaped like a pear, the small end being slightly incurved and +produced into a long curved filament, or _cilium_, of extreme tenuity. +Behind this, from the concave side of the incurvation, proceeded another +long cilium, so delicate as to be discernible only by the use of the +highest powers and careful management of the light. In the centre of the +pear-shaped body a clear round space could occasionally be discerned, but +not always; and careful watching showed that this clear vacuity appeared +gradually, and then shut up and disappeared suddenly, at regular +intervals. Such a structure is of common occurrence among the lowest +plants and animals, and is known as a _contractile vacuole_. + +The little creature thus described sometimes propelled itself with great +activity, with a curious rolling motion, by the lashing of the front +cilium, while the second cilium trailed behind; sometimes it anchored +itself by the hinder cilium and was spun round by the working of the +other, its motions resembling those of an anchor buoy in a heavy sea. +Sometimes, when two were in full career towards one another, each would +appear dexterously to get out of the other's way; sometimes a crowd would +assemble and jostle one another, with as much semblance of individual +effort as a spectator on the Grands Mulets might observe with a telescope +among the specks representing men in the valley of Chamounix. + +The spectacle, though always surprising, was not new to me. So my reply +to the question put to me was, that these organisms were what biologists +call _Monads_, and though they might be animals, it was also possible +that they might, like the _Bacteria_, be plants. My friend received my +verdict with an expression which showed a sad want of respect for +authority. He would as soon believe that a sheep was a plant. Naturally +piqued by this want of faith, I have thought a good deal over the matter; +and, as I still rest in the lame conclusion I originally expressed, and +must even now confess that I cannot certainly say whether this creature +is an animal or a plant, I think it may be well to state the grounds of +my hesitation at length. But, in the first place, in order that I may +conveniently distinguish this "Monad" from the multitude of other things +which go by the same designation, I must give it a name of its own. I +think (though, for reasons which need not be stated at present, I am not +quite sure) that it is identical with the species _Monas lens_ as defined +by the eminent French microscopist Dujardin, though his magnifying power +was probably insufficient to enable him to see that it is curiously like +a much larger form of monad which he has named _Heteromita_. I shall, +therefore, call it not _Monas_, but _Heteromita lens_. + +I have been unable to devote to my _Heteromita_ the prolonged study +needful to work out its whole history, which would involve weeks, or it +may be months, of unremitting attention. But I the less regret this +circumstance, as some remarkable observations recently published by +Messrs. Dallinger and Drysdale[5] on certain Monads, relate, in part, to +a form so similar to my _Heteromita lens_, that the history of the one +may be used to illustrate that of the other. These most patient and +painstaking observers, who employed the highest attainable powers of the +microscope and, relieving one another, kept watch day and night over the +same individual monads, have been enabled to trace out the whole history +of their _Heteromita_; which they found in infusions of the heads of +fishes of the Cod tribe. + +[Footnote 5: "Researches in the Life-history of a Cercomonad: a Lesson in +Biogenesis"; and "Further Researches in the Life-history of the Monads," +--_Monthly Microscopical Journal_, 1873.] + +Of the four monads described and figured by these investigators, one, as +I have said, very closely resembles _Heteromita lens_ in every +particular, except that it has a separately distinguishable central +particle or "nucleus," which is not certainly to be made out in +_Heteromita lens_; and that nothing is said by Messrs. Dallinger and +Drysdale of the existence of a contractile vacuole in this monad, though +they describe it in another. + +Their _Heteromita_, however, multiplied rapidly by fission. Sometimes a +transverse constriction appeared; the hinder half developed a new cilium, +and the hinder cilium gradually split from its base to its free end, +until it was divided into two; a process which, considering the fact that +this fine filament cannot be much more than 1/100000 of an inch in +diameter, is wonderful enough. The constriction of the body extended +inwards until the two portions were united by a narrow isthmus; finally, +they separated and each swam away by itself, a complete _Heteromita_, +provided with its two cilia. Sometimes the constriction took a +longitudinal direction, with the same ultimate result. In each case the +process occupied not more than six or seven minutes. At this rate, a +single _Heteromita_ would give rise to a thousand like itself in the +course of an hour, to about a million in two hours, and to a number +greater than the generally assumed number of human beings now living in +the world in three hours; or, if we give each _Heteromita_ an hour's +enjoyment of individual existence, the same result will be obtained in +about a day. The apparent suddenness of the appearance of multitudes of +such organisms as these in any nutritive fluid to which one obtains +access is thus easily explained. + +During these processes of multiplication by fission, the _Heteromita_ +remains active; but sometimes another mode of fission occurs. The body +becomes rounded and quiescent, or nearly so; and, while in this resting +state, divides into two portions, each of which is rapidly converted into +an active _Heteromita_. + +A still more remarkable phenomenon is that kind of multiplication which +is preceded by the union of two monads, by a process which is termed +_conjugation_. Two active _Heteromitoe_ become applied to one another, +and then slowly and gradually coalesce into one body. The two nuclei run +into one; and the mass resulting from the conjugation of the two +_Heteromitoe_, thus fused together, has a triangular form. The two pairs +of cilia are to be seen, for some time, at two of the angles, which +answer to the small ends of the conjoined monads; but they ultimately +vanish, and the twin organism, in which all visible traces of +organisation have disappeared, falls into a state of rest. Sudden wave- +like movements of its substance next occur; and, in a short time, the +apices of the triangular mass burst, and give exit to a dense yellowish, +glairy fluid, filled with minute granules. This process, which, it will +be observed, involves the actual confluence and mixture of the substance +of two distinct organisms, is effected in the space of about two hours. + +The authors whom I quote say that they "cannot express" the excessive +minuteness of the granules in question, and they estimate their diameter +at less than 1/200000 of an inch. Under the highest powers of the +microscope, at present applicable, such specks are hardly discernible. +Nevertheless, particles of this size are massive when compared to +physical molecules; whence there is no reason to doubt that each, small +as it is, may have a molecular structure sufficiently complex to give +rise to the phenomena of life. And, as a matter of fact, by patient +watching of the place at which these infinitesimal living particles were +discharged, our observers assured themselves of their growth and +development into new monads. In about four hours from their being set +free, they had attained a sixth of the length of the parent, with the +characteristic cilia, though at first they were quite motionless; and, in +four hours more, they had attained the dimensions and exhibited all the +activity of the adult. These inconceivably minute particles are therefore +the germs of the _Heteromita_; and from the dimensions of these germs it +is easily shown that the body formed by conjugation may, at a low +estimate, have given exit to thirty thousand of them; a result of a +matrimonial process whereby the contracting parties, without a metaphor, +"become one flesh," enough to make a Malthusian despair of the future of +the Universe. + +I am not aware that the investigators from whom I have borrowed this +history have endeavoured to ascertain whether their monads take solid +nutriment or not; so that though they help us very much to fill up the +blanks in the history of my _Heteromita_, their observations throw no +light on the problem we are trying to solve--Is it an animal or is it a +plant? + +Undoubtedly it is possible to bring forward very strong arguments in +favour of regarding _Heteromita_ as a plant. + +For example, there is a Fungus, an obscure and almost microscopic mould, +termed _Peronospora infestans_. Like many other Fungi, the _Peronosporoe_ +are parasitic upon other plants; and this particular _Peronospora_ +happens to have attained much notoriety and political importance, in a +way not without a parallel in the career of notorious politicians, +namely, by reason of the frightful mischief it has done to mankind. For +it is this _Fungus_ which is the cause of the potato disease; and, +therefore, _Peronospora infestans_ (doubtless of exclusively Saxon +origin, though not accurately known to be so) brought about the Irish +famine. The plants afflicted with the malady are found to be infested by +a mould, consisting of fine tubular filaments, termed _hyphoe_, which +burrow through the substance of the potato plant, and appropriate to +themselves the substance of their host; while, at the same time, directly +or indirectly, they set up chemical changes by which even its woody +framework becomes blackened, sodden, and withered. + +In structure, however, the _Peronospora_ is as much a mould as the common +_Penicillium_; and just as the _Penicillium_ multiplies by the breaking +up of its hyphoe into separate rounded bodies, the spores; so, in the +_Peronospora_, certain of the hyphoe grow out into the air through the +interstices of the superficial cells of the potato plant, and develop +spores. Each of these hyphoe usually gives off several branches. The ends +of the branches dilate and become closed sacs, which eventually drop off +as spores. The spores falling on some part of the same potato plant, or +carried by the wind to another, may at once germinate, throwing out +tubular prolongations which become hyphoe, and burrow into the substance +of the plant attacked. But, more commonly, the contents of the spore +divide into six or eight separate portions. The coat of the spore gives +way, and each portion then emerges as an independent organism, which has +the shape of a bean, rather narrower at one end than the other, convex on +one side, and depressed or concave on the opposite. From the depression, +two long and delicate cilia proceed, one shorter than the other, and +directed forwards. Close to the origin of these cilia, in the substance +of the body, is a regularly pulsating, contractile vacuole. The shorter +cilium vibrates actively, and effects the locomotion of the organism, +while the other trails behind; the whole body rolling on its axis with +its pointed end forwards. + +The eminent botanist, De Bary, who was not thinking of our problem, tells +us, in describing the movements of these "Zoospores," that, as they swim +about, "Foreign bodies are carefully avoided, and the whole movement has +a deceptive likeness to the voluntary changes of place which are observed +in microscopic animals." + +After swarming about in this way in the moisture on the surface of a leaf +or stem (which, film though it may be, is an ocean to such a fish) for +half an hour, more or less, the movement of the zoospore becomes slower, +and is limited to a slow turning upon its axis, without change of place. +It then becomes quite quiet, the cilia disappear, it assumes a spherical +form, and surrounds itself with a distinct, though delicate, membranous +coat. A protuberance then grows out from one side of the sphere, and +rapidly increasing in length, assumes the character of a hypha. The +latter penetrates into the substance of the potato plant, either by +entering a stomate, or by boring through the wall of an epidermic cell, +and ramifies, as a mycelium, in the substance of the plant, destroying +the tissues with which it comes in contact. As these processes of +multiplication take place very rapidly, millions of spores are soon set +free from a single infested plant; and, from their minuteness, they are +readily transported by the gentlest breeze. Since, again, the zoospores +set free from each spore, in virtue of their powers of locomotion, +swiftly disperse themselves over the surface, it is no wonder that the +infection, once started, soon spreads from field to field, and extends +its ravages over a whole country. + +However, it does not enter into my present plan to treat of the potato +disease, instructively as its history bears upon that of other epidemics; +and I have selected the case of the _Peroganspora_ simply because it +affords an example of an organism, which, in one stage of its existence, +is truly a "Monad," indistinguishable by any important character from our +_Heteromita_, and extraordinarily like it in some respects. And yet this +"Monad" can be traced, step by step, through the series of metamorphoses +which I have described, until it assumes the features of an organism, +which is as much a plant as is an oak or an elm. + +Moreover, it would be possible to pursue the analogy farther. Under +certain circumstances, a process of conjugation takes place in the +_Peronospora_. Two separate portions of its protoplasm become fused +together, surround themselves with a thick coat and give rise to a sort +of vegetable egg called an _oospore_. After a period of rest, the +contents of the oospore break up into a number of zoospores like those +already described, each of which, after a period of activity, germinates +in the ordinary way. This process obviously corresponds with the +conjugation and subsequent setting free of germs in the _Heteromita_. + +But it may be said that the _Peronospora_ is, after all, a questionable +sort of plant; that it seems to be wanting in the manufacturing power, +selected as the main distinctive character of vegetable life; or, at any +rate, that there is no proof that it does not get its protein matter +ready made from the potato plant. + +Let us, therefore, take a case which is not open to these objections. + +There are some small plants known to botanists as members of the genus +_Colcochaete_, which, without being truly parasitic, grow upon certain +water-weeds, as lichens grow upon trees. The little plant has the form of +an elegant green star, the branching arms of which are divided into +cells. Its greenness is due to its chlorophyll, and it undoubtedly has +the manufacturing power in full degree, decomposing carbonic acid and +setting oxygen free, under the influence of sunlight. But the +protoplasmic contents of some of the cells of which the plant is made up +occasionally divide, by a method similar to that which effects the +division of the contents of the _Peronospora_ spore; and the severed +portions are then set free as active monad-like zoospores. Each is oval +and is provided at one extremity with two long active cilia. Propelled by +these, it swims about for a longer or shorter time, but at length comes +to a state of rest and gradually grows into a _Coleochaete_. Moreover, as +in the _Peronospora_, conjugation may take place and result in an +oospore; the contents of which divide and are set free as monadiform +germs. + +If the whole history of the zoospores of _Peronospora_ and of +_Coleochaete_ were unknown, they would undoubtedly be classed among +"Monads" with the same right as _Heteromita_; why then may not +_Heteromita_ be a plant, even though the cycle of forms through which it +passes shows no terms quite so complex as those which occur in +_Peronospora_ and _Coleochaete_? And, in fact, there are some green +organisms, in every respect characteristically plants, such as +_Chlamydomonas_, and the common _Volvox_, or so-called "Globe +animalcule," which run through a cycle of forms of just the same simple +character as those of _Heteromita_. + +The name of _Chlamydomonas_ is applied to certain microscopic green +bodies, each of which consists of a protoplasmic central substance +invested by a structureless sac. The latter contains cellulose, as in +ordinary plants; and the chlorophyll which gives the green colour enables +the _Chlamydomonas_ to decompose carbonic acid and fix carbon as they do. +Two long cilia protrude through the cell-wall, and effect the rapid +locomotion of this "monad," which, in all respects except its mobility, +is characteristically a plant. Under ordinary circumstances, the +_Chlamydomonas_ multiplies by simple fission, each splitting into two or +into four parts, which separate and become independent organisms. +Sometimes, however, the _Chlamydomonas_ divides into eight parts, each of +which is provided with four instead of two cilia. These "zoospores" +conjugate in pairs, and give rise to quiescent bodies, which multiply by +division, find eventually pass into the active state. + +Thus, so far as outward form and the general character of the cycle of +modifications, through which the organism passes in the course of its +life, are concerned, the resemblance between _Chlamydomonas_ and +_Heteromita_ is of the closest description. And on the face of the matter +there is no ground for refusing to admit that _Heteromita_ may be related +to _Chlamydomonas_, as the colourless fungus is to the green alga. +_Volvox_ may be compared to a hollow sphere, the wall of which is made up +of coherent Chlamydomonads; and which progresses with a rotating motion +effected by the paddling of the multitudinous pairs of cilia which +project from its surface. Each _Volvox_-monad, moreover, possesses a red +pigment spot, like the simplest form of eye known among animals. The +methods of fissive multiplication and of conjugation observed in the +monads of this locomotive globe are essentially similar to those observed +in _Chlamydomonas_; and, though a hard battle has been fought over it, +_Volvox_ is now finally surrendered to the Botanists. + +Thus there is really no reason why _Heteromita_ may not be a plant; and +this conclusion would be very satisfactory, if it were not equally easy +to show that there is really no reason why it should not be an animal. +For there are numerous organisms presenting the closest resemblance to +_Heteromita_, and, like it, grouped under the general name of "Monads," +which, nevertheless, can be observed to take in solid nutriment, and +which, therefore, have a virtual, if not an actual, mouth and digestive +cavity, and thus come under Cuvier's definition of an animal. Numerous +forms of such animals have been described by Ehrenberg, Dujardin, H. +James Clark, and other writers on the _Infusoria_. Indeed, in another +infusion of hay in which my _Heteromita lens_ occurred, there were +innumerable such infusorial animalcules belonging to the well-known +species _Colpoda cucullus_.[6] + +[Footnote 6: Excellently described by Stein, almost all of whose +statements I have verified.] + +Full-sized specimens of this animalcule attain a length of between 1/300 +or 1/400 of an inch, so that it may have ten times the length and a +thousand times the mass of a _Heteromita_. In shape, it is not altogether +unlike _Heteromita_. The small end, however, is not produced into one +long cilium, but the general surface of the body is covered with small +actively vibrating ciliary organs, which are only longest at the small +end. At the point which answers to that from which the two cilia arise in +_Heteromita_, there is a conical depression, the mouth; and, in young +specimens, a tapering filament, which reminds one of the posterior cilium +of _Heteromita_, projects from this region. + +The body consists of a soft granular protoplasmic substance, the middle +of which is occupied by a large oval mass called the "nucleus"; while, at +its hinder end, is a "contractile vacuole," conspicuous by its regular +rhythmic appearances and disappearances. Obviously, although the +_Colpoda_ is not a monad, it differs from one only in subordinate +details. Moreover, under certain conditions, it becomes quiescent, +incloses itself in a delicate case or _cyst_, and then divides into two, +four, or more portions, which are eventually set free and swim about as +active _Colpodoe_. + +But this creature is an unmistakable animal, and full-sized _Colpodoe_ +may be fed as easily as one feeds chickens. It is only needful to diffuse +very finely ground carmine through the water in which they live, and, in +a very short time, the bodies of the _Colpodoe_ are stuffed with the +deeply-coloured granules of the pigment. + +And if this were not sufficient evidence of the animality of _Colpoda_, +there comes the fact that it is even more similar to another well-known +animalcule, _Paramoecium_, than it is to a monad. But _Paramoecium_ is so +huge a creature compared with those hitherto discussed--it reaches 1/120 +of an inch or more in length--that there is no difficulty in making out +its organisation in detail; and in proving that it is not only an animal, +but that it is an animal which possesses a somewhat complicated +organisation. For example, the surface layer of its body is different in +structure from the deeper parts. There are two contractile vacuoles, from +each of which radiates a system of vessel-like canals; and not only is +there a conical depression continuous with a tube, which serve as mouth +and gullet, but the food ingested takes a definite course, and refuse is +rejected from a definite region. Nothing is easier than to feed these +animals, and to watch the particles of indigo or carmine accumulate at +the lower end of the gullet. From this they gradually project, surrounded +by a ball of water, which at length passes with a jerk, oddly simulating +a gulp, into the pulpy central substance of the body, there to circulate +up one side and down the other, until its contents are digested and +assimilated. Nevertheless, this complex animal multiplies by division, as +the monad does, and, like the monad, undergoes conjugation. It stands in +the same relation to _Heteromita_ on the animal side, as _Coleochaete_ +does on the plant side. Start from either, and such an insensible series +of gradations leads to the monad that it is impossible to say at any +stage of the progress where the line between the animal and the plant +must be drawn. + +There is reason to think that certain organisms which pass through a +monad stage of existence, such as the _Myxomycetes_, are, at one time of +their lives, dependent upon external sources for their protein matter, or +are animals; and, at another period, manufacture it, or are plants. And +seeing that the whole progress of modern investigation is in favour of +the doctrine of continuity, it is a fair and probable speculation--though +only a speculation--that, as there are some plants which can manufacture +protein out of such apparently intractable mineral matters as carbonic +acid, water, nitrate of ammonia, metallic and earthy salts; while others +need to be supplied with their carbon and nitrogen in the somewhat less +raw form of tartrate of ammonia and allied compounds; so there may be yet +others, as is possibly the case with the true parasitic plants, which can +only manage to put together materials still better prepared--still more +nearly approximated to protein--until we arrive at such organisms as the +_Psorospermioe_ and the _Panhistophyton_, which are as much animal as +vegetable in structure, but are animal in their dependence on other +organisms for their food. + +The singular circumstance observed by Meyer, that the _Torula_ of yeast, +though an indubitable plant, still flourishes most vigorously when +supplied with the complex nitrogenous substance, pepsin; the probability +that the _Peronospora_ is nourished directly by the protoplasm of the +potato-plant; and the wonderful facts which have recently been brought to +light respecting insectivorous plants, all favour this view; and tend to +the conclusion that the difference between animal and plant is one of +degree rather than of kind, and that the problem whether, in a given +case, an organism is an animal or a plant, may be essentially insoluble. + + + +VII + + +A LOBSTER; OR, THE STUDY OF ZOOLOGY + +[1861] + +Natural history is the name familiarly applied to the study of the +properties of such natural bodies as minerals, plants, and animals; the +sciences which embody the knowledge man has acquired upon these subjects +are commonly termed Natural Sciences, in contradistinction to other so- +called "physical" sciences; and those who devote themselves especially to +the pursuit of such sciences have been and are commonly termed +"Naturalists." + +Linnaeus was a naturalist in this wide sense, and his "Systema Naturae" was +a work upon natural history, in the broadest acceptation of the term; in +it, that great methodising spirit embodied all that was known in his time +of the distinctive characters of minerals, animals, and plants. But the +enormous stimulus which Linnaeus gave to the investigation of nature soon +rendered it impossible that any one man should write another "Systema +Naturae," and extremely difficult for any one to become even a naturalist +such as Linnaeus was. + +Great as have been the advances made by all the three branches of +science, of old included under the title of natural history, there can be +no doubt that zoology and botany have grown in an enormously greater +ratio than mineralogy; and hence, as I suppose, the name of "natural +history" has gradually become more and more definitely attached to these +prominent divisions of the subject, and by "naturalist" people have meant +more and more distinctly to imply a student of the structure and function +of living beings. + +However this may be, it is certain that the advance of knowledge has +gradually widened the distance between mineralogy and its old associates, +while it has drawn zoology and botany closer together; so that of late +years it has been found convenient (and indeed necessary) to associate +the sciences which deal with vitality and all its phenomena under the +common head of "biology"; and the biologists have come to repudiate any +blood-relationship with their foster-brothers, the mineralogists. + +Certain broad laws have a general application throughout both the animal +and the vegetable worlds, but the ground common to these kingdoms of +nature is not of very wide extent, and the multiplicity of details is so +great, that the student of living beings finds himself obliged to devote +his attention exclusively either to the one or the other. If he elects to +study plants, under any aspect, we know at once what to call him. He is a +botanist, and his science is botany. But if the investigation of animal +life be his choice, the name generally applied to him will vary according +to the kind of animals he studies, or the particular phenomena of animal +life to which he confines his attention. If the study of man is his +object, he is called an anatomist, or a physiologist, or an ethnologist; +but if he dissects animals, or examines into the mode in which their +functions are performed, he is a comparative anatomist or comparative +physiologist. If he turns his attention to fossil animals, he is a +palaeontologist. If his mind is more particularly directed to the specific +description, discrimination, classification, and distribution of animals, +he is termed a zoologist. + +For the purpose of the present discourse, however, I shall recognise none +of these titles save the last, which I shall employ as the equivalent of +botanist, and I shall use the term zoology is denoting the whole doctrine +of animal life, in contradistinction to botany, which signifies the whole +doctrine of vegetable life. + +Employed in this sense, zoology, like botany, is divisible into three +great but subordinate sciences, morphology, physiology, and distribution, +each of which may, to a very great extent, be studied independently of +the other. + +Zoological morphology is the doctrine of animal form or structure. +Anatomy is one of its branches; development is another; while +classification is the expression of the relations which different animals +bear to one another, in respect of their anatomy and their development. + +Zoological distribution is the study of animals in relation to the +terrestrial conditions which obtain now, or have obtained at any previous +epoch of the earth's history. + +Zoological physiology, lastly, is the doctrine of the functions or +actions of animals. It regards animal bodies as machines impelled by +certain forces, and performing an amount of work which can be expressed +in terms of the ordinary forces of nature. The final object of physiology +is to deduce the facts of morphology, on the one hand, and those of +distribution on the other, from the laws of the molecular forces of +matter. + +Such is the scope of zoology. But if I were to content myself with the +enunciation of these dry definitions, I should ill exemplify that method +of teaching this branch of physical science, which it is my chief +business to-night to recommend. Let us turn away then from abstract +definitions. Let us take some concrete living thing, some animal, the +commoner the better, and let us see how the application of common sense +and common logic to the obvious facts it presents, inevitably leads us +into all these branches of zoological science. + +I have before me a lobster. When I examine it, what appears to be the +most striking character it presents? Why, I observe that this part which +we call the tail of the lobster, is made up of six distinct hard rings +and a seventh terminal piece. If I separate one of the middle rings, say +the third, I find it carries upon its under surface a pair of limbs or +appendages, each of which consists of a stalk and two terminal pieces. So +that I can represent a transverse section of the ring and its appendages +upon the diagram board in this way. + +If I now take the fourth ring, I find it has the same structure, and so +have the fifth and the second; so that, in each of these divisions of the +tail, I find parts which correspond with one another, a ring and two +appendages; and in each appendage a stalk and two end pieces. These +corresponding parts are called, in the technical language of anatomy, +"homologous parts." The ring of the third division is the "homologue" of +the ring of the fifth, the appendage of the former is the homologue of +the appendage of the latter. And, as each division exhibits corresponding +parts in corresponding places, we say that all the divisions are +constructed upon the same plan. But now let us consider the sixth +division. It is similar to, and yet different from, the others. The ring +is essentially the same as in the other divisions; but the appendages +look at first as if they were very different; and yet when we regard them +closely, what do we find? A stalk and two terminal divisions, exactly as +in the others, but the stalk is very short and very thick, the terminal +divisions are very broad and flat, and one of them is divided into two +pieces. + +I may say, therefore, that the sixth segment is like the others in plan, +but that it is modified in its details. + +The first segment is like the others, so far as its ring is concerned, +and though its appendages differ from any of those yet examined in the +simplicity of their structure, parts corresponding with the stem and one +of the divisions of the appendages of the other segments can be readily +discerned in them. + +Thus it appears that the lobster's tail is composed of a series of +segments which are fundamentally similar, though each presents peculiar +modifications of the plan common to all. But when I turn to the forepart +of the body I see, at first, nothing but a great shield-like shell, +called technically the "carapace," ending in front in a sharp spine, on +either side of which are the curious compound eyes, set upon the ends of +stout movable stalks. Behind these, on the under side of the body, are +two pairs of long feelers, or antennae, followed by six pairs of jaws +folded against one another over the mouth, and five pairs of legs, the +foremost of these being the great pinchers, or claws, of the lobster. + +It looks, at first, a little hopeless to attempt to find in this complex +mass a series of rings, each with its pair of appendages, such as I have +shown you in the abdomen, and yet it is not difficult to demonstrate +their existence. Strip off the legs, and you will find that each pair is +attached to a very definite segment of the under wall of the body; but +these segments, instead of being the lower parts of free rings, as in the +tail, are such parts of rings which are all solidly united and bound +together; and the like is true of the jaws, the feelers, and the eye- +stalks, every pair of which is borne upon its own special segment. Thus +the conclusion is gradually forced upon us, that the body of the lobster +is composed of as many rings as there are pairs of appendages, namely, +twenty in all, but that the six hindmost rings remain free and movable, +while the fourteen front rings become firmly soldered together, their +backs forming one continuous shield--the carapace. + +Unity of plan, diversity in execution, is the lesson taught by the study +of the rings of the body, and the same instruction is given still more +emphatically by the appendages. If I examine the outermost jaw I find it +consists of three distinct portions, an inner, a middle, and an outer, +mounted upon a common stem; and if I compare this jaw with the legs +behind it, or the jaws in front of it, I find it quite easy to see, that, +in the legs, it is the part of the appendage which corresponds with the +inner division, which becomes modified into what we know familiarly as +the "leg," while the middle division disappears, and the outer division +is hidden under the carapace. Nor is it more difficult to discern that, +in the appendages of the tail, the middle division appears again and the +outer vanishes; while, on the other hand, in the foremost jaw, the so- +called mandible, the inner division only is left; and, in the same way, +the parts of the feelers and of the eye-stalks can be identified with +those of the legs and jaws. + +But whither does all this tend? To the very remarkable conclusion that a +unity of plan, of the same kind as that discoverable in the tail or +abdomen of the lobster, pervades the whole organisation of its skeleton, +so that I can return to the diagram representing any one of the rings of +the tail, which I drew upon the board, and by adding a third division to +each appendage, I can use it as a sort of scheme or plan of any ring of +the body. I can give names to all the parts of that figure, and then if I +take any segment of the body of the lobster, I can point out to you +exactly, what modification the general plan has undergone in that +particular segment; what part has remained movable, and what has become +fixed to another; what has been excessively developed and metamorphosed +and what has been suppressed. + +But I imagine I hear the question, How is all this to be tested? No doubt +it is a pretty and ingenious way of looking at the structure of any +animal; but is it anything more? Does Nature acknowledge, in any deeper +way, this unity of plan we seem to trace? + +The objection suggested by these questions is a very valid and important +one, and morphology was in an unsound state so long as it rested upon the +mere perception of the analogies which obtain between fully formed parts. +The unchecked ingenuity of speculative anatomists proved itself fully +competent to spin any number of contradictory hypotheses out of the same +facts, and endless morphological dreams threatened to supplant scientific +theory. + +Happily, however, there is a criterion of morphological truth, and a sure +test of all homologies. Our lobster has not always been what we see it; +it was once an egg, a semifluid mass of yolk, not so big as a pin's head, +contained in a transparent membrane, and exhibiting not the least trace +of any one of those organs, the multiplicity and complexity of which, in +the adult, are so surprising. After a time, a delicate patch of cellular +membrane appeared upon one face of this yolk, and that patch was the +foundation of the whole creature, the clay out of which it would be +moulded. Gradually investing the yolk, it became subdivided by transverse +constrictions into segments, the forerunners of the rings of the body. +Upon the ventral surface of each of the rings thus sketched out, a pair +of bud-like prominences made their appearance--the rudiments of the +appendages of the ring. At first, all the appendages were alike, but, as +they grew, most of them became distinguished into a stem and two terminal +divisions, to which, in the middle part of the body, was added a third +outer division; and it was only at a later period, that by the +modification, or absorption, of certain of these primitive constituents, +the limbs acquired their perfect form. + +Thus the study of development proves that the doctrine of unity of plan +is not merely a fancy, that it is not merely one way of looking at the +matter, but that it is the expression of deep-seated natural facts. The +legs and jaws of the lobster may not merely be regarded as modifications +of a common type,--in fact and in nature they are so,--the leg and the +jaw of the young animal being, at first, indistinguishable. + +These are wonderful truths, the more so because the zoologist finds them +to be of universal application. The investigation of a polype, of a +snail, of a fish, of a horse, or of a man, would have led us, though by a +less easy path, perhaps, to exactly the same point. Unity of plan +everywhere lies hidden under the mask of diversity of structure--the +complex is everywhere evolved out of the simple. Every animal has at +first the form of an egg, and every animal and every organic part, in +reaching its adult state, passes through conditions common to other +animals and other adult parts; and this leads me to another point. I have +hitherto spoken as if the lobster were alone in the world, but, as I need +hardly remind you, there are myriads of other animal organisms. Of these, +some, such as men, horses, birds, fishes, snails, slugs, oysters, corals, +and sponges, are not in the least like the lobster. But other animals, +though they may differ a good deal from the lobster, are yet either very +like it, or are like something that is like it. The cray fish, the rock +lobster, and the prawn, and the shrimp, for example, however different, +are yet so like lobsters, that a child would group them as of the lobster +kind, in contradistinction to snails and slugs; and these last again +would form a kind by themselves, in contradistinction to cows, horses, +and sheep, the cattle kind. + +But this spontaneous grouping into "kinds" is the first essay of the +human mind at classification, or the calling by a common name of those +things that are alike, and the arranging them in such a manner as best to +suggest the sum of their likenesses and unlikenesses to other things. + +Those kinds which include no other subdivisions than the sexes, or +various breeds, are called, in technical language, species. The English +lobster is a species, our cray fish is another, our prawn is another. In +other countries, however, there are lobsters, cray fish, and prawns, very +like ours, and yet presenting sufficient differences to deserve +distinction. Naturalists, therefore, express this resemblance and this +diversity by grouping them as distinct species of the same "genus." But +the lobster and the cray fish, though belonging to distinct genera, have +many features in common, and hence are grouped together in an assemblage +which is called a family. More distant resemblances connect the lobster +with the prawn and the crab, which are expressed by putting all these +into the same order. Again, more remote, but still very definite, +resemblances unite the lobster with the woodlouse, the king crab, the +water flea, and the barnacle, and separate them from all other animals; +whence they collectively constitute the larger group, or class, +_Crustacea_. But the _Crustacea_ exhibit many peculiar features in common +with insects, spiders, and centipedes, so that these are grouped into the +still larger assemblage or "province" _Articulata_; and, finally, the +relations which these have to worms and other lower animals, are +expressed by combining the whole vast aggregate into the sub-kingdom of +_Annulosa_. + +If I had worked my way from a sponge instead of a lobster, I should have +found it associated, by like ties, with a great number of other animals +into the sub-kingdom _Protozoa_; if I had selected a fresh-water polype +or a coral, the members of what naturalists term the sub-kingdom +_Coelenterata_, would have grouped themselves around my type; had a snail +been chosen, the inhabitants of all univalve and bivalve, land and water, +shells, the lamp shells, the squids, and the sea-mat would have gradually +linked themselves on to it as members of the same sub-kingdom of +_Mollusca_; and finally, starting from man, I should have been compelled +to admit first, the ape, the rat, the horse, the dog, into the same +class; and then the bird, the crocodile, the turtle, the frog, and the +fish, into the same sub-kingdom of _Vertebrata_. + +And if I had followed out all these various lines of classification +fully, I should discover in the end that there was no animal, either +recent or fossil, which did not at once fall into one or other of these +sub-kingdoms. In other words, every animal is organised upon one or other +of the five, or more, plans, the existence of which renders our +classification possible. And so definitely and precisely marked is the +structure of each animal, that, in the present state of our knowledge, +there is not the least evidence to prove that a form, in the slightest +degree transitional between any of the two groups _Vertebrata, Annulosa, +Mollusca_, and _Coelenterata_, either exists, or has existed, during that +period of the earth's history which is recorded by the geologist.[1] +Nevertheless, you must not for a moment suppose, because no such +transitional forms are known, that the members of the sub-kingdoms are +disconnected from, or independent of, one another. On the contrary, in +their earliest condition they are all similar, and the primordial germs +of a man, a dog, a bird, a fish, a beetle, a snail, and a polype are, in +no essential structural respects, distinguishable. + +[Footnote 1: The different grouping necessitated by later knowledge does +not affect the principle of the argument.--1894.] + +In this broad sense, it may with truth be said, that all living animals, +and all those dead faunae which geology reveals, are bound together by an +all-pervading unity of organisation, of the same character, though not +equal in degree, to that which enables us to discern one and the same +plan amidst the twenty different segments of a lobster's body. Truly it +has been said, that to a clear eye the smallest fact is a window through +which the Infinite may be seen. + +Turning from these purely morphological considerations, let us now +examine into the manner in which the attentive study of the lobster +impels us into other lines of research. + +Lobsters are found in all the European seas; but on the opposite shores +of the Atlantic and in the seas of the southern hemisphere they do not +exist. They are, however, represented in these regions by very closely +allied, but distinct forms--the _Homarus Americanus_ and the _Homarus +Capensis:_ so that we may say that the European has one species of +_Homuarus_; the American, another; the African, another; and thus the +remarkable facts of geographical distribution begin to dawn upon us. + +Again, if we examine the contents of the earth's crust, we shall find in +the latter of those deposits, which have served as the great burying +grounds of past ages, numberless lobster-like animals, but none so +similar to our living lobster as to make zoologists sure that they +belonged even to the same genus. If we go still further back in time, we +discover, in the oldest rocks of all, the remains of animals, constructed +on the same general plan as the lobster, and belonging to the same great +group of _Crustacea_; but for the most part totally different from the +lobster, and indeed from any other living form of crustacean; and thus we +gain a notion of that successive change of the animal population of the +globe, in past ages, which is the most striking fact revealed by geology. + +Consider, now, where our inquiries have led us. We studied our type +morphologically, when we determined its anatomy and its development, and +when comparing it, in these respects, with other animals, we made out its +place in a system of classification. If we were to examine every animal +in a similar manner, we should establish a complete body of zoological +morphology. + +Again, we investigated the distribution of our type in space and in time, +and, if the like had been done with every animal, the sciences of +geographical and geological distribution would have attained their limit. + +But you will observe one remarkable circumstance, that, up to this point, +the question of the life of these organisms has not come under +consideration. Morphology and distribution might be studied almost as +well, if animals and plants were a peculiar kind of crystals, and +possessed none of those functions which distinguish living beings so +remarkably. But the facts of morphology and distribution have to be +accounted for, and the science, the aim of which it is to account for +them, is Physiology. + +Let us return to our lobster once more. If we watched the creature in its +native element, we should see it climbing actively the submerged rocks, +among which it delights to live, by means of its strong legs; or swimming +by powerful strokes of its great tail, the appendages of the sixth joint +of which are spread out into a broad fan-like Propeller: seize it, and it +will show you that its great claws are no mean weapons of offence; +suspend a piece of carrion among its haunts, and it will greedily devour +it, tearing and crushing the flesh by means of its multitudinous jaws. + +Suppose that we had known nothing of the lobster but as an inert mass, an +organic crystal, if I may use the phrase, and that we could suddenly see +it exerting all these powers, what wonderful new ideas and new questions +would arise in our minds! The great new question would be, "How does all +this take place?" the chief new idea would be, the idea of adaptation to +purpose,--the notion, that the constituents of animal bodies are not mere +unconnected parts, but organs working together to an end. Let us consider +the tail of the lobster again from this point of view. Morphology has +taught us that it is a series of segments composed of homologous parts, +which undergo various modifications--beneath and through which a common +plan of formation is discernible. But if I look at the same part +physiologically, I see that it is a most beautifully constructed organ of +locomotion, by means of which the animal can swiftly propel itself either +backwards or forwards. + +But how is this remarkable propulsive machine made to perform its +functions? If I were suddenly to kill one of these animals and to take +out all the soft parts, I should find the shell to be perfectly inert, to +have no more power of moving itself than is possessed by the machinery of +a mill when disconnected from its steam-engine or water-wheel. But if I +were to open it, and take out the viscera only, leaving the white flesh, +I should perceive that the lobster could bend and extend its tail as well +as before. If I were to cut off the tail, I should cease to find any +spontaneous motion in it; but on pinching any portion of the flesh, I +should observe that it underwent a very curious change--each fibre +becoming shorter and thicker. By this act of contraction, as it is +termed, the parts to which the ends of the fibre are attached are, of +course, approximated; and according to the relations of their points of +attachment to the centres of motions of the different rings, the bending +or the extension of the tail results. Close observation of the newly- +opened lobster would soon show that all its movements are due to the same +cause--the shortening and thickening of these fleshy fibres, which are +technically called muscles. + +Here, then, is a capital fact. The movements of the lobster are due to +muscular contractility. But why does a muscle contract at one time and +not at another? Why does one whole group of muscles contract when the +lobster wishes to extend his tail, and another group when he desires to +bend it? What is it originates, directs, and controls the motive power? + +Experiment, the great instrument for the ascertainment of truth in +physical science, answers this question for us. In the head of the +lobster there lies a small mass of that peculiar tissue which is known as +nervous substance. Cords of similar matter connect his brain of the +lobster, directly or indirectly, with the muscles. Now, if these +communicating cords are cut, the brain remaining entire, the power of +exerting what we call voluntary motion in the parts below the section is +destroyed; and, on the other hand, if, the cords remaining entire, the +brain mass be destroyed, the same voluntary mobility is equally lost. +Whence the inevitable conclusion is, that the power of originating these +motions resides in the brain and is propagated along the nervous cords. + +In the higher animals the phenomena which attend this transmission have +been investigated, and the exertion of the peculiar energy which resides +in the nerves has been found to be accompanied by a disturbance of the +electrical state of their molecules. + +If we could exactly estimate the signification of this disturbance; if we +could obtain the value of a given exertion of nerve force by determining +the quantity of electricity, or of heat, of which it is the equivalent; +if we could ascertain upon what arrangement, or other condition of the +molecules of matter, the manifestation of the nervous and muscular +energies depends (and doubtless science will some day or other ascertain +these points), physiologists would have attained their ultimate goal in +this direction; they would have determined the relation of the motive +force of animals to the other forms of force found in nature; and if the +same process had been successfully performed for all the operations which +are carried on in, and by, the animal frame, physiology would be perfect, +and the facts of morphology and distribution would be deducible from the +laws which physiologists had established, combined with those determining +the condition of the surrounding universe. + +There is not a fragment of the organism of this humble animal whose study +would not lead us into regions of thought as large as those which I have +briefly opened up to you; but what I have been saying, I trust, has not +only enabled you to form a conception of the scope and purport of +zoology, but has given you an imperfect example of the manner in which, +in my opinion, that science, or indeed any physical science, may be best +taught. The great matter is, to make teaching real and practical, by +fixing the attention of the student on particular facts; but at the same +time it should be rendered broad and comprehensive, by constant reference +to the generalisations of which all particular facts are illustrations. +The lobster has served as a type of the whole animal kingdom, and its +anatomy and physiology have illustrated for us some of the greatest +truths of biology. The student who has once seen for himself the facts +which I have described, has had their relations explained to him, and has +clearly comprehended them, has, so far, a knowledge of zoology, which is +real and genuine, however limited it may be, and which is worth more than +all the mere reading knowledge of the science he could ever acquire. His +zoological information is, so far, knowledge and not mere hearsay. + +And if it were nay business to fit you for the certificate in zoological +science granted by this department, I should pursue a course precisely +similar in principle to that which I have taken to-night. I should select +a fresh-water sponge, a fresh-water polype or a _Cyanoea_, a fresh-water +mussel, a lobster, a fowl, as types of the five primary divisions of the +animal kingdom. I should explain their structure very fully, and show how +each illustrated the great principles of zoology. Having gone very +carefully and fully over this ground, I should feel that you had a safe +foundation, and I should then take you in the same way, but less +minutely, over similarly selected illustrative types of the classes; and +then I should direct your attention to the special forms enumerated under +the head of types, in this syllabus, and to the other facts there +mentioned. + +That would, speaking generally, be my plan. But I have undertaken to +explain to you the best mode of acquiring and communicating a knowledge +of zoology, and you may therefore fairly ask me for a more detailed and +precise account of the manner in which I should propose to furnish you +with the information I refer to. + +My own impression is, that the best model for all kinds of training in +physical science is that afforded by the method of teaching anatomy, in +use in the medical schools. This method consists of three elements-- +lectures, demonstrations, and examinations. + +The object of lectures is, in the first place, to awaken the attention +and excite the enthusiasm of the student; and this, I am sure, may be +effected to a far greater extent by the oral discourse and by the +personal influence of a respected teacher than in any other way. +Secondly, lectures have the double use of guiding the student to the +salient points of a subject, and at the same time forcing him to attend +to the whole of it, and not merely to that part which takes his fancy. +And lastly, lectures afford the student the opportunity of seeking +explanations of those difficulties which will, and indeed ought to, arise +in the course of his studies. + +What books shall I read? is a question constantly put by the student to +the teacher. My reply usually is, "None: write your notes out carefully +and fully; strive to understand them thoroughly; come to me for the +explanation of anything you cannot understand; and I would rather you did +not distract your mind by reading." A properly composed course of +lectures ought to contain fully as much matter as a student can +assimilate in the time occupied by its delivery; and the teacher should +always recollect that his business is to feed, and not to cram the +intellect. Indeed, I believe that a student who gains from a course of +lectures the simple habit of concentrating his attention upon a +definitely limited series of facts, until they are thoroughly mastered, +has made a step of immeasurable importance. + +But, however good lectures may be, and however extensive the course of +reading by which they are followed up, they are but accessories to the +great instrument of scientific teaching--demonstration. If I insist +unweariedly, nay fanatically, upon the importance of physical science as +an educational agent, it is because the study of any branch of science, +if properly conducted, appears to me to fill up a void left by all other +means of education. I have the greatest respect and love for literature; +nothing would grieve me more than to see literary training other than a +very prominent branch of education: indeed, I wish that real literary +discipline were far more attended to than it is; but I cannot shut my +eyes to the fact, that there is a vast difference between men who have +had a purely literary, and those who have had a sound scientific, +training. + +Seeking for the cause of this difference, I imagine I can find it in the +fact that, in the world of letters, learning and knowledge are one, and +books are the source of both; whereas in science, as in life, learning +and knowledge are distinct, and the study of things, and not of books, is +the source of the latter. + +All that literature has to bestow may be obtained by reading and by +practical exercise in writing and in speaking; but I do not exaggerate +when I say, that none of the best gifts of science are to be won by these +means. On the contrary, the great benefit which a scientific education +bestows, whether is training or as knowledge, is dependent upon the +extent to which the mind of the student is brought into immediate contact +with facts--upon the degree to which he learns the habit of appealing +directly to Nature, and of acquiring through his senses concrete images +of those properties of things, which are, and always will be, but +approximatively expressed in human language. Our way of looking at +Nature, and of speaking about her, varies from year to year; but a fact +once seen, a relation of cause and effect, once demonstratively +apprehended, are possessions which neither change nor pass away, but, on +the contrary, form fixed centres, about which other truths aggregate by +natural affinity. + +Therefore, the great business of the scientific teacher is, to imprint +the fundamental, irrefragable facts of his science, not only by words +upon the mind, but by sensible impressions upon the eye, and ear, and +touch of the student, in so complete a manner, that every term used, or +law enunciated, should afterwards call up vivid images of the particular +structural, or other, facts which furnished the demonstration of the law, +or the illustration of the term. + +Now this important operation can only be achieved by constant +demonstration, which may take place to a certain imperfect extent during +a lecture, but which ought also to be carried on independently, and which +should be addressed to each individual student, the teacher endeavouring, +not so much to show a thing to the learner, as to make him see it for +himself. + +I am well aware that there are great practical difficulties in the way of +effectual zoological demonstrations. The dissection of animals is not +altogether pleasant, and requires much time; nor is it easy to secure an +adequate supply of the needful specimens. The botanist has here a great +advantage; his specimens are easily obtained, are clean and wholesome, +and can be dissected in a private house as well as anywhere else; and +hence, I believe, the fact, that botany is so much more readily and +better taught than its sister science. But, be it difficult or be it +easy, if zoological science is to be properly studied, demonstration, +and, consequently, dissection, must be had. Without it, no man can have a +really sound knowledge of animal organisation. + +A good deal may be done, however, without actual dissection on the +student's part, by demonstration upon specimens and preparations; and in +all probability it would not be very difficult, were the demand +sufficient, to organise collections of such objects, sufficient for all +the purposes of elementary teaching, at a comparatively cheap rate. Even +without these, much might be effected, if the zoological collections, +which are open to the public, were arranged according to what has been +termed the "typical principle"; that is to say, if the specimens exposed +to public view were so selected that the public could learn something +from them, instead of being, as at present, merely confused by their +multiplicity. For example, the grand ornithological gallery at the +British Museum contains between two and three thousand species of birds, +and sometimes five or six specimens of a species. They are very pretty to +look at, and some of the cases are, indeed, splendid; but I will +undertake to say, that no man but a professed ornithologist has ever +gathered much information from the collection. Certainly, no one of the +tens of thousands of the general public who have walked through that +gallery ever knew more about the essential peculiarities of birds when he +left the gallery than when he entered it. But if, somewhere in that vast +hall, there were a few preparations, exemplifying the leading structural +peculiarities and the mode of development of a common fowl; if the types +of the genera, the leading modifications in the skeleton, in the plumage +at various ages, in the mode of nidification, and the like, among birds, +were displayed; and if the other specimens were put away in a place where +the men of science, to whom they are alone useful, could have free access +to them, I can conceive that this collection might become a great +instrument of scientific education. + +The last implement of the teacher to which I have adverted is +examination--a means of education now so thoroughly understood that I +need hardly enlarge upon it. I hold that both written and oral +examinations are indispensable, and, by requiring the description of +specimens, they may be made to supplement demonstration. + +Such is the fullest reply the time at my disposal will allow me to give +to the question--how may a knowledge of zoology be best acquired and +communicated? + +But there is a previous question which may be moved, and which, in fact, +I know many are inclined to move. It is the question, why should teachers +be encouraged to acquire a knowledge of this, or any other branch of +physical science? What is the use, it is said, of attempting to make +physical science a branch of primary education? Is it not probable that +teachers, in pursuing such studies, will be led astray from the +acquirement of more important but less attractive knowledge? And, even if +they can learn something of science without prejudice to their +usefulness, what is the good of their attempting to instil that knowledge +into boys whose real business is the acquisition of reading, writing, and +arithmetic? + +These questions are, and will be, very commonly asked, for they arise +from that profound ignorance of the value and true position of physical +science, which infests the minds of the most highly educated and +intelligent classes of the community. But if I did not feel well assured +that they are capable of being easily and satisfactorily answered; that +they have been answered over and over again; and that the time will come +when men of liberal education will blush to raise such questions--I +should be ashamed of my position here to-night. Without doubt, it is your +great and very important function to carry out elementary education; +without question, anything that should interfere with the faithful +fulfilment of that duty on your part would be a great evil; and if I +thought that your acquirement of the elements of physical science, and +your communication of those elements to your pupils, involved any sort of +interference with your proper duties, I should be the first person to +protest against your being encouraged to do anything of the kind. + +But is it true that the acquisition of such a knowledge of science as is +proposed, and the communication of that knowledge, are calculated to +weaken your usefulness? Or may I not rather ask, is it possible for you +to discharge your functions properly without these aids? + +What is the purpose of primary intellectual education? I apprehend that +its first object is to train the young in the use of those tools +wherewith men extract knowledge from the ever-shifting succession of +phenomena which pass before their eyes; and that its second object is to +inform them of the fundamental laws which have been found by experience +to govern the course of things, so that they may not be turned out into +the world naked, defenceless, and a prey to the events they might +control. + +A boy is taught to read his own and other languages, in order that he may +have access to infinitely wider stores of knowledge than could ever be +opened to him by oral intercourse with his fellow men; he learns to +write, that his means of communication with the rest of mankind may be +indefinitely enlarged, and that he may record and store up the knowledge +he acquires. He is taught elementary mathematics, that he may understand +all those relations of number and form, upon which the transactions of +men, associated in complicated societies, are built, and that he may have +some practice in deductive reasoning. + +All these operations of reading, writing, and ciphering, are intellectual +tools, whose use should, before all things, be learned, and learned +thoroughly; so that the youth may be enabled to make his life that which +it ought to be, a continual progress in learning and in wisdom. + +But, in addition, primary education endeavours to fit a boy out with a +certain equipment of positive knowledge. He is taught the great laws of +morality; the religion of his sect; so much history and geography as will +tell him where the great countries of the world are, what they are, and +how they have become what they are. + +Without doubt all these are most fitting and excellent things to teach a +boy; I should be very sorry to omit any of them from any scheme of +primary intellectual education. The system is excellent, so far as it +goes. + +But if I regard it closely, a curious reflection arises. I suppose that, +fifteen hundred years ago, the child of any well-to-do Roman citizen was +taught just these same things; reading and writing in his own, and, +perhaps, the Greek tongue; the elements of mathematics; and the religion, +morality, history, and geography current in his time. Furthermore, I do +not think I err in affirming, that, if such a Christian Roman boy, who +had finished his education, could be transplanted into one of our public +schools, and pass through its course of instruction, he would not meet +with a single unfamiliar line of thought; amidst all the new facts he +would have to learn, not one would suggest a different mode of regarding +the universe from that current in his own time. + +And yet surely there is some great difference between the civilisation of +the fourth century and that of the nineteenth, and still more between the +intellectual habits and tone of thought of that day and this? + +And what has made this difference? I answer fearlessly--The prodigious +development of physical science within the last two centuries. + +Modern civilisation rests upon physical science; take away her gifts to +our own country, and our position among the leading nations of the world +is gone to-morrow; for it is physical science only that makes +intelligence and moral energy stronger than brute force. + +The whole of modern thought is steeped in science; it has made its way +into the works of our best poets, and even the mere man of letters, who +affects to ignore and despise science, is unconsciously impregnated with +her spirit, and indebted for his best products to her methods. I believe +that the greatest intellectual revolution mankind has yet seen is now +slowly taking place by her agency. She is teaching the world that the +ultimate court of appeal is observation and experiment, and not +authority; she is teaching it to estimate the value of evidence; she is +creating a firm and living faith in the existence of immutable moral and +physical laws, perfect obedience to which is the highest possible aim of +an intelligent being. + +But of all this your old stereotyped system of education takes no note. +Physical science, its methods, its problems, and its difficulties, will +meet the poorest boy at every turn, and yet we educate him in such a +manner that he shall enter the world as ignorant of the existence of the +methods and facts of science as the day he was born. The modern world is +full of artillery; and we turn out our children to do battle in it, +equipped with the shield and sword of an ancient gladiator. + +Posterity will cry shame on us if we do not remedy this deplorable state +of things. Nay, if we live twenty years longer, our own consciences will +cry shame on us. + +It is my firm conviction that the only way to remedy it is to make the +elements of physical science an integral part of primary education. I +have endeavoured to show you how that may be done for that branch of +science which it is my business to pursue; and I can but add, that I +should look upon the day when every schoolmaster throughout this land was +a centre of genuine, however rudimentary, scientific knowledge, as an +epoch in the history of the country. + +But let me entreat you to remember my last words. Addressing myself to +you, as teachers, I would say, mere book learning in physical science is +a sham and a delusion--what you teach, unless you wish to be impostors, +that you must first know; and real knowledge in science means personal +acquaintance with the facts, be they few or many.[2] + +[Footnote 2: It has been suggested to me that these words may be taken to +imply a discouragement on my part of any sort of scientific instruction +which does not give an acquaintance with the facts at first hand. But +this is not my meaning. The ideal of scientific teaching is, no doubt, a +system by which the scholar sees every fact for himself, and the teacher +supplies only the explanations. Circumstances, however, do not often +allow of the attainment of that ideal, and we must put up with the next +best system--one in which the scholar takes a good deal on trust from a +teacher, who, knowing the facts by his own knowledge, can describe them +with so much vividness as to enable his audience to form competent ideas +concerning them. The system which I repudiate is that which allows +teachers who have not come into direct contact with the leading facts of +a science to pass their second-hand information on. The scientific virus, +like vaccine lymph, if passed through too long a succession of organisms, +will lose all its effect in protecting the young against the intellectual +epidemics to which they are exposed. + +[The remarks on p. 222 applied to the Natural History Collection of the +British Museum in 1861. The visitor to the Natural History Museum in 1894 +need go no further than the Great Hall to see the realisation of my hopes +by the present Director.]] + + + +VIII + + +BIOGENESIS AND ABIOGENESIS + +(THE PRESIDENTIAL ADDRESS TO THE BRITISH ASSOCIATION FOR THE ADVANCEMENT +OF SCIENCE FOR 1870) + +It has long been the custom for the newly installed President of the +British Association for the Advancement of Science to take advantage of +the elevation of the position in which the suffrages of his colleagues +had, for the time, placed him, and, casting his eyes around the horizon +of the scientific world, to report to them what could be seen from his +watch-tower; in what directions the multitudinous divisions of the noble +army of the improvers of natural knowledge were marching; what important +strongholds of the great enemy of us all, ignorance, had been recently +captured; and, also, with due impartiality, to mark where the advanced +posts of science had been driven in, or a long-continued siege had made +no progress. + +I propose to endeavour to follow this ancient precedent, in a manner +suited to the limitations of my knowledge and of my capacity. I shall not +presume to attempt a panoramic survey of the world of science, nor even +to give a sketch of what is doing in the one great province of biology, +with some portions of which my ordinary occupations render me familiar. +But I shall endeavour to put before you the history of the rise and +progress of a single biological doctrine; and I shall try to give some +notion of the fruits, both intellectual and practical, which we owe, +directly or indirectly, to the working out, by seven generations of +patient and laborious investigators, of the thought which arose, more +than two centuries ago, in the mind of a sagacious and observant Italian +naturalist. + +It is a matter of everyday experience that it is difficult to prevent +many articles of food from becoming covered with mould; that fruit, sound +enough to all appearance, often contains grubs at the core; that meat, +left to itself in the air, is apt to putrefy and swarm with maggots. Even +ordinary water, if allowed to stand in an open vessel, sooner or later +becomes turbid and full of living matter. + +The philosophers of antiquity, interrogated as to the cause of these +phenomena, were provided with a ready and a plausible answer. It did not +enter their minds even to doubt that these low forms of life were +generated in the matters in which they made their appearance. Lucretius, +who had drunk deeper of the scientific spirit than any poet of ancient or +modern times except Goethe, intends to speak as a philosopher, rather +than as a poet, when he writes that "with good reason the earth has +gotten the name of mother, since all things are produced out of the +earth. And many living creatures, even now, spring out of the earth, +taking form by the rains and the heat of the sun."[1] The axiom of +ancient science, "that the corruption of one thing is the birth of +another," had its popular embodiment in the notion that a seed dies +before the young plant springs from it; a belief so widespread and so +fixed, that Saint Paul appeals to it in one of the most splendid +outbursts of his fervid eloquence:-- + +"Thou fool, that which thou sowest is not quickened, except it die."[2] + +[Footnote 1: It is thus that Mr. Munro renders + +"Linquitur, ut merito maternum nomen adepta +Terra sit, e terra quoniam sunt cuncta creata. +Multaque nunc etiam exsistant animalia terris +Imbribus et calido solis concreta vapore." + +_De Rerum Natura_, lib. v. 793-796. + +But would not the meaning of the last line be better rendered "Developed +in rain-water and in the warm vapours raised by the sun"?] + +[Footnote 2: 1 Corinthians xv. 36.] + +The proposition that life may, and does, proceed from that which has no +life, then, was held alike by the philosophers, the poets, and the +people, of the most enlightened nations, eighteen hundred years ago; and +it remained the accepted doctrine of learned and unlearned Europe, +through the Middle Ages, down even to the seventeenth century. + +It is commonly counted among the many merits of our great countryman, +Harvey, that he was the first to declare the opposition of fact to +venerable authority in this, as in other matters; but I can discover no +justification for this widespread notion. After careful search through +the "Exercitationes de Generatione," the most that appears clear to me +is, that Harvey believed all animals and plants to spring from what he +terms a "_primordium vegetale_," a phrase which may nowadays be rendered +"a vegetative germ"; and this, he says, is _"oviforme_," or "egg-like"; +not, he is careful to add, that it necessarily has the shape of an egg, +but because it has the constitution and nature of one. That this +"_primordium oviforme_" must needs, in all cases, proceed from a living +parent is nowhere expressly maintained by Harvey, though such an opinion +may be thought to be implied in one or two passages; while, on the other +hand, he does, more than once, use language which is consistent only with +a full belief in spontaneous or equivocal generation.[3] In fact, the +main concern of Harvey's wonderful little treatise is not with +generation, in the physiological sense, at all, but with development; and +his great object is the establishment of the doctrine of epigenesis. + +[Footnote 3: See the following passage in Exercitatio I.:--"Item _sponte +nascentia_ dicuntur; non quod ex _putredine_ oriunda sint, sed quod casu, +naturae sponte, et aequivoca (ut aiunt) generatione, a parentibus sui +dissimilibus proveniant." Again, in _De Uteri Membranis:_--"In cunctorum +viventium generatione (sicut diximus) hoc solenne est, ut ortum ducunt a +_primordio_ aliquo, quod tum materiam tum elficiendi potestatem in se +habet: sitque, adeo id, ex quo et a quo quicquid nascitur, ortum suum +ducat. Tale primordium in animalibus (_sive ab aliis generantibus +proveniant, sive sponte, aut ex putredine nascentur_) est humor in +tunica, aliquaaut putami ne conclusus." Compare also what Redi has to say +respecting Harvey's opinions, _Esperienze_, p. 11.] + +The first distinct enunciation of the hypothesis that all living matter +has sprung from pre-existing living matter, came from a contemporary, +though a junior, of Harvey, a native of that country, fertile in men +great in all departments of human activity, which was to intellectual +Europe, in the sixteenth and seventeenth centuries, what Germany is in +the nineteenth. It was in Italy, and from Italian teachers, that Harvey +received the most important part of his scientific education. And it was +a student trained in the same schools, Francesco Redi--a man of the +widest knowledge and most versatile abilities, distinguished alike as +scholar, poet, physician, and naturalist--who, just two hundred and two +years ago, published his "Esperienze intorno alla Generazione degl' +Insetti," and gave to the world the idea, the growth of which it is my +purpose to trace. Redi's book went through five editions in twenty years; +and the extreme simplicity of his experiments, and the clearness of his +arguments, gained for his views, and for their consequences, almost +universal acceptance. + +Redi did not trouble himself much with speculative considerations, but +attacked particular cases of what was supposed to be "spontaneous +generation" experimentally. Here are dead animals, or pieces of meat, +says he; I expose them to the air in hot weather, and in a few days they +swarm with maggots. You tell me that these are generated in the dead +flesh; but if I put similar bodies, while quite fresh, into a jar, and +tie some fine gauze over the top of the jar, not a maggot makes its +appearance, while the dead substances, nevertheless, putrefy just in the +same way as before. It is obvious, therefore, that the maggots are not +generated by the corruption of the meat; and that the cause of their +formation must be a something which is kept away by gauze. But gauze will +not keep away aeriform bodies, or fluids. This something must, therefore, +exist in the form of solid particles too big to get through the gauze. +Nor is one long left in doubt what these solid particles are; for the +blowflies, attracted by the odour of the meat, swarm round the vessel, +and, urged by a powerful but in this case misleading instinct, lay eggs +out of which maggots are immediately hatched, upon the gauze. The +conclusion, therefore, is unavoidable; the maggots are not generated by +the meat, but the eggs which give rise to them are brought through the +air by the flies. + +These experiments seem almost childishly simple, and one wonders how it +was that no one ever thought of them before. Simple as they are, however, +they are worthy of the most careful study, for every piece of +experimental work since done, in regard to this subject, has been shaped +upon the model furnished by the Italian philosopher. As the results of +his experiments were the same, however varied the nature of the materials +he used, it is not wonderful that there arose in Redi's mind a +presumption, that, in all such cases of the seeming production of life +from dead matter, the real explanation was the introduction of living +germs from without into that dead matter.[4] And thus the hypothesis that +living matter always arises by the agency of pre-existing living matter, +took definite shape; and had, henceforward, a right to be considered and +a claim to be refuted, in each particular case, before the production of +living matter in any other way could be admitted by careful reasoners. It +will be necessary for me to refer to this hypothesis so frequently, that, +to save circumlocution, I shall call it the hypothesis of _Biogenesis_; +and I shall term the contrary doctrine--that living matter may be +produced by not living matter--the hypothesis of _Abiogenesis_. + +[Footnote 4: "Pure contentandomi sempre in questa ed in ciascuna altro +cosa, da ciascuno piu savio, la dove io difettuosamente parlassi, esser +corretto; non tacero, che per molte osservazioni molti volti da me fatte, +mi sento inclinato a credere che la terra, da quelle prime piante, e da +quei primi animali in poi, che ella nei primi giorni del mondo produsse +per comandemento del sovrano ed omnipotente Fattore, non abbia mai piu +prodotto da se medesima ne erba ne albero, ne animale alcuno perfetto o +imperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassati +e nato e che ora nascere in lei, o da lei veggiamo, venga tutto dalla +semenza reale e vera delle piante, e degli animali stessi, i quali col +mezzo del proprio seme la loro spezie conservano. E se bene tutto giorno +scorghiamo da' cadaveri degli animali, e da tutte quante le maniere dell' +erbe, e de' fiori, e dei frutti imputriditi, e corrotti nascere vermi +infiniti-- + +'Nonne vides quaecunque mora, fluidoque calore +Corpora tabescunt in parva animalia verti'-- + +Io mi sento, dico, inclinato, a credere che tutti quei vermi si generino +dal seme paterno; e che le carni, e l' erbe, e l' altre cose tutte +putrefatte, o putrefattibili non facciano altra parte, ne abbiano altro +ufizio nella generazione degl' insetti, se non d'apprestare un luogo o un +nido proporzionato, in cui dagli animali nel tempo della figliatura sieno +portati, e partoriti i vermi, o l' uova o l' altre semenze dei vermi, i +quali tosto che nati sono, trovano in esso nido un sufficiente alimento +abilissimo per nutricarsi: e se in quello non son portate dalle madri +queste suddette semenze, niente mai, e replicatamente niente, vi s' +ingegneri e nasca."--REDI, _Esperienze_, pp. 14-16.] + +In the seventeenth century, as I have said, the latter was the dominant +view, sanctioned alike by antiquity and by authority; and it is +interesting to observe that Redi did not escape the customary tax upon a +discoverer of having to defend himself against the charge of impugning +the authority of the Scriptures;[5] for his adversaries declared that the +generation of bees from the carcase of a dead lion is affirmed, in the +Book of Judges, to have been the origin of the famous riddle with which +Samson perplexed the Philistines:-- + +Out of the eater came forth meat, +And out of the strong came forth sweetness. + +[Footnote 5: "Molti, e molti altri ancora vi potrei annoverare, se non +fossi chiamato a rispondere alle rampogne di alcuni, che bruscamente mi +rammentano cio, che si legge nel capitolo quattordicesimo del sacrosanto +Libro de' giudici ... "--REDI, _loc. cit._ p. 45.] + +Against all odds, however, Redi, strong with the strength of demonstrable +fact, did splendid battle for Biogenesis; but it is remarkable that he +held the doctrine in a sense which, if he lead lived in these times, +would have infallibly caused him to be classed among the defenders of +"spontaneous generation." "Omne vivum ex vivo," "no life without +antecedent life," aphoristically sums up Redi's doctrine; but he went no +further. It is most remarkable evidence of the philosophic caution and +impartiality of his mind, that although he had speculatively anticipated +the manner in which grubs really are deposited in fruits and in the galls +of plants, he deliberately admits that the evidence is insufficient to +bear him out; and he therefore prefers the supposition that they are +generated by a modification of the living substance of the plants +themselves. Indeed, he regards these vegetable growths as organs, by +means of which the plant gives rise to an animal, and looks upon this +production of specific animals as the final cause of the galls and of, at +any rate, some fruits. And he proposes to explain the occurrence of +parasites within the animal body in the same way.[6] + +[Footnote 6: The passage (_Esperienze_, p. 129) is worth quoting in +full:-- + +"Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi, +gli alberi e le foglie, in due maniere inverminassero. Una, perche +venendo i bachi per di fuora, e cercando l' alimento, col rodere ci +aprono la strada, ed arrivano alla piu interna midolla de' frutti e de' +legni. L'altra maniera si e, che io per me stimerei, che non fosse gran +fatto disdicevole il credere, che quell' anima o quella virtu, la quale +genera i fiori ed i frutti nelle piante viventi, sia quella stessa che +generi ancora i bachi di esse piante. E chi sa, forse, che molti frutti +degli alberi non sieno prodotti, non per un fine primario e principale, +ma bensi per un uffizio secondario e servile, destinato alla generazione +di que' vermi, servendo a loro in vece di matrice, in cui dimorino un +prefisso e determinato tempo; il quale arrivato escan fuora a godere il +sole. + +"Io m' immagino, che questo mio pensiero non vi parra totalmento un +paradosso; mentro farete riflessione a quelle tanto sorte di galle, di +gallozzole, di coccole, di ricci, di calici, di cornetti ed i lappole, +che son produtte dalle quercel, dalle farnie, da' cerri, da' sugheri, da' +leeci e da altri simili alberi de ghianda; imperciocche in quello +gallozzole, e particolarmente nelle piu grosse, che si chiamano coronati, +ne' ricci capelluti, che ciuffoli da' nostri contadini son detti; nei +ricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzze +della foglia del leccio si vede evidentissimamente, che la prima e +principale intenzione della natura e formare dentro di quelle un animale +volante; vedendosi nel centro della gallozzola un uovo, che col crescere +e col maturarsi di essa gallozzola va crescendo e maturando anch' egli, e +cresce altresi a suo tempo quel verme, che nell' uovo si racchiude; il +qual verme, quando la gallozzola e finita di maturare e che e venuto il +termine destinato al suo nascimento, diventa, di verme che era, una +mosca.... Io vi confesso ingenuamente, che prima d'aver fatte queste mie +esperienze intorno alla generazione degl' insetti mi dava a credere, o +per dir meglio sospettava, che forse la gallozzola nascesse, perche +arrivando la mosca nel tempo della primavera, e facendo una piccolissima +fessura ne' rami piu teneri della quercia, in quella fessura nascondesse +uno de suoi semi, il quale fosse cagione che sbocciasse fuora la +gallozzola; e che mai non si vedessero galle o gallozzole o ricci o +cornetti o calici o coccole, se non in que' rami, ne' quali le mosche +avessero depositate le loro semenze; e mi dava ad intendere, che le +gallozzole fossero una malattia cagionata nelle querce dalle punture +delle mosche, in quella giusa stessa che dalle punture d'altri animaletti +simiglievoli veggiamo crescere de' tumori ne' corpi degli animali."] + +It is of great importance to apprehend Redi's position rightly; for the +lines of thought he laid down for us are those upon which naturalists +have been working ever since. Clearly, he held _Biogenesis_ as against +_Abiogenesis;_ and I shall immediately proceed, in the first place, to +inquire how far subsequent investigation has borne him out in so doing. + +But Redi also thought that there were two modes of Biogenesis. By the one +method, which is that of common and ordinary occurrence, the living +parent gives rise to offspring which passes through the same cycle of +changes as itself--like gives rise to like; and this has been termed +_Homogenesis_. By the other mode, the living parent was supposed to give +rise to offspring which passed through a totally different series of +states from those exhibited by the parent, and did not return into the +cycle of the parent; this is what ought to be called _Heterogenesis_, the +offspring being altogether, and permanently, unlike the parent. The term +Heterogenesis, however, has unfortunately been used in a different sense, +and M. Milne-Edwards has therefore substituted for it _Xenogenesis_, +which means the generation of something foreign. After discussing Redi's +hypothesis of universal Biogenesis, then, I shall go on to ask how far +the growth of science justifies his other hypothesis of Xenogenesis. + +The progress of the hypothesis of Biogenesis was triumphant and unchecked +for nearly a century. The application of the microscope to anatomy in the +hands of Grew, Leeuwenhoek, Swammerdam, Lyonnet, Vallisnieri, Reaurnur, +and other illustrious investigators of nature of that day, displayed such +a complexity of organisation in the lowest and minutest forms, and +everywhere revealed such a prodigality of provision for their +multiplication by germs of one sort or another, that the hypothesis of +Abiogenesis began to appear not only untrue, but absurd; and, in the +middle of the eighteenth century, when Needham and Buffon took up the +question, it was almost universally discredited.[7] + +[Footnote 7: Needham, writing in 1750, says:-- + +"Les naturalistes modernes s'accordent unaninement a etablir, comme une +verite certaine, que toute plante vient do sa semence specifique, tout +animal d'un oeuf ou de quelque chose d'analogue preexistant dans la +plante, ou dans l'animal de meme espece qui l'a produit."--_Nouvelles +Observations_, p. 169. + +"Les naturalistes out generalemente cru que les animaux microscopiques +etaient engendres par des oeufs transportes dans l'air, ou deposes dans +des eaux dormantes par des insectes volans."--_Ibid._ p. 176.] + +But the skill of the microscope makers of the eighteenth century soon +reached its limit. A microscope magnifying 400 diameters was a _chef +d'oeuvre_ of the opticians of that day; and, at the same time, by no +means trustworthy. But a magnifying power of 400 diameters, even when +definition reaches the exquisite perfection of our modern achromatic +lenses, hardly suffices for the mere discernment of the smallest forms of +life. A speck, only 1/25th of an inch in diameter, has, at ten inches +from the eye, the same apparent size as an object 1/10000th of an inch in +diameter, when magnified 400 times; but forms of living matter abound, +the diameter of which is not more than 1/40000th of an inch. A filtered +infusion of hay, allowed to stand for two days, will swarm with living +things among which, any which reaches the diameter of a human red blood- +corpuscle, or about 1/3200th of an inch, is a giant. It is only by +bearing these facts in mind, that we can deal fairly with the remarkable +statements and speculations put forward by Buffon and Needham in the +middle of the eighteenth century. + +When a portion of any animal or vegetable body is infused in water, it +gradually softens and disintegrates; and, as it does so, the water is +found to swarm with minute active creatures, the so-called Infusorial +Animalcules, none of which can be seen, except by the aid of the +microscope; while a large proportion belong to the category of smallest +things of which I have spoken, and which must have looked like mere dots +and lines under the ordinary microscopes of the eighteenth century. + +Led by various theoretical considerations which I cannot now discuss, but +which looked promising enough in the lights of their time, Buffon and +Needham doubted the applicability of Redi's hypothesis to the infusorial +animalcules, and Needham very properly endeavoured to put the question to +an experimental test. He said to himself, If these infusorial animalcules +come from germs, their germs must exist either in the substance infused, +or in the water with which the infusion is made, or in the superjacent +air. Now the vitality of all germs is destroyed by heat. Therefore, if I +boil the infusion, cork it up carefully, cementing the cork over with +mastic, and then heat the whole vessel by heaping hot ashes over it, I +must needs kill whatever germs are present. Consequently, if Redi's +hypothesis hold good, when the infusion is taken away and allowed to +cool, no animalcules ought to be developed in it; whereas, if the +animalcules are not dependent on pre-existing germs, but are generated +from the infused substance, they ought, by and by, to make their +appearance. Needham found that, under the circumstances in which he made +his experiments, animalcules always did arise in the infusions, when a +sufficient time had elapsed to allow for their development. + +In much of his work Needham was associated with Buffon, and the results +of their experiments fitted in admirably with the great French +naturalist's hypothesis of "organic molecules," according to which, life +is the indefeasible property of certain indestructible molecules of +matter, which exist in all living things, and have inherent activities by +which they are distinguished from not living matter. Each individual +living organism is formed by their temporary combination. They stand to +it in the relation of the particles of water to a cascade, or a +whirlpool; or to a mould, into which the water is poured. The form of the +organism is thus determined by the reaction between external conditions +and the inherent activities of the organic molecules of which it is +composed; and, as the stoppage of a whirlpool destroys nothing but a +form, and leaves the molecules of the water, with all their inherent +activities intact, so what we call the death and putrefaction of an +animal, or of a plant, is merely the breaking up of the form, or manner +of association, of its constituent organic molecules, which are then set +free as infusorial animalcules. + +It will be perceived that this doctrine is by no means identical with +_Abiogenesis_, with which it is often confounded. On this hypothesis, a +piece of beef, or a handful of hay, is dead only in a limited sense. The +beef is dead ox, and the hay is dead grass; but the "organic molecules" +of the beef or the hay are not dead, but are ready to manifest their +vitality as soon as the bovine or herbaceous shrouds in which they are +imprisoned are rent by the macerating action of water. The hypothesis +therefore must be classified under Xenogenesis, rather than under +Abiogenesis. Such as it was, I think it will appear, to those who will be +just enough to remember that it was propounded before the birth of modern +chemistry, and of the modern optical arts, to be a most ingenious and +suggestive speculation. + +But the great tragedy of Science--the slaying of a beautiful hypothesis +by an ugly fact--which is so constantly being enacted under the eyes of +philosophers, was played, almost immediately, for the benefit of Buffon +and Needham. + +Once more, an Italian, the Abbe Spallanzani, a worthy successor and +representative of Redi in his acuteness, his ingenuity, and his learning, +subjected the experiments and the conclusions of Needham to a searching +criticism. It might be true that Needham's experiments yielded results +such as he had described, but did they bear out his arguments? Was it not +possible, in the first place, he had not completely excluded the air by +his corks and mastic? And was it not possible, in the second place, that +he had not sufficiently heated his infusions and the superjacent air? +Spallanzani joined issue with the English naturalist on both these pleas, +and he showed that if, in the first place, the glass vessels in which the +infusions were contained were hermetically sealed by fusing their necks, +and if, in the second place, they were exposed to the temperature of +boiling water for three-quarters of an hour,[8] no animalcules ever made +their appearance within them. It must be admitted that the experiments +and arguments of Spallanzani furnish a complete and a crushing reply to +those of Needham. But we all too often forget that it is one thing to +refute a proposition, and another to prove the truth of a doctrine which, +implicitly or explicitly, contradicts that proposition; and the advance +of science soon showed that though Needham might be quite wrong, it did +not follow that Spallanzani was quite right. + +[Footnote 8: See Spallanzani, _Opere_, vi. pp. 42 and 51.] + +Modern Chemistry, the birth of the latter half of the eighteenth century, +grew apace, and soon found herself face to face with the great problems +which biology had vainly tried to attack without her help. The discovery +of oxygen led to the laying of the foundations of a scientific theory of +respiration, and to an examination of the marvellous interactions of +organic substances with oxygen. The presence of free oxygen appeared to +be one of the conditions of the existence of life, and of those singular +changes in organic matters which are known as fermentation and +putrefaction. The question of the generation of the infusory animalcules +thus passed into a new phase. For what might not have happened to the +organic matter of the infusions, or to the oxygen of the air, in +Spallanzani's experiments? What security was there that the development +of life which ought to have taken place had not been checked or prevented +by these changes? + +The battle had to be fought again. It was needful to repeat the +experiments under conditions which would make sure that neither the +oxygen of the air, nor the composition of the organic matter, was altered +in such a manner as to interfere with the existence of life. + +Schulze and Schwann took up the question from this point of view in 1836 +and 1837. The passage of air through red-hot glass tubes, or through +strong sulphuric acid, does not alter the proportion of its oxygen, while +it must needs arrest, or destroy, any organic matter which may be +contained in the air. These experimenters, therefore, contrived +arrangements by which the only air which should come into contact with a +boiled infusion should be such as had either passed through red-hot tubes +or through strong sulphuric acid. The result which they obtained was that +an infusion so treated developed no living things, while, if the same +infusion was afterwards exposed to the air, such things appeared rapidly +and abundantly. The accuracy of these experiments has been alternately +denied and affirmed. Supposing then, to be accepted, however, all that +they really proved was that the treatment to which the air was subjected +destroyed _something_ that was essential to the development of life in +the infusion. This "something" might be gaseous, fluid, or solid; that it +consisted of germs remained only an hypothesis of greater or less +probability. + +Contemporaneously with these investigations a remarkable discovery was +made by Cagniard de la Tour. He found that common yeast is composed of a +vast accumulation of minute plants. The fermentation of must, or of wort, +in the fabrication of wine and of beer, is always accompanied by the +rapid growth and multiplication of these _Toruloe_. Thus, fermentation, +in so far as it was accompanied by the development of microscopical +organisms in enormous numbers, became assimilated to the decomposition of +an infusion of ordinary animal or vegetable matter; and it was an obvious +suggestion that the organisms were, in some way or other, the causes both +of fermentation and of putrefaction. The chemists, with Berzelius and +Liebig at their head, at first laughed this idea to scorn; but in 1843, a +man then very young, who has since performed the unexampled feat of +attaining to high eminence alike in Mathematics, Physics, and Physiology-- +I speak of the illustrious Helmholtz--reduced the matter to the test of +experiment by a method alike elegant and conclusive. Helmholtz separated +a putrefying or a fermenting liquid from one which was simply putrescible +or fermentable by a membrane which allowed the fluids to pass through and +become intermixed, but stopped the passage of solids. The result was, +that while the putrescible or the fermentable liquids became impregnated +with the results of the putrescence or fermentation which was going on on +the other side of the membrane, they neither putrefied (in the ordinary +way) nor fermented; nor were any of the organisms which abounded in the +fermenting or putrefying liquid generated in them. Therefore the cause of +the development of these organisms must lie in something which cannot +pass through membranes; and as Helmholtz's investigations were long +antecedent to Graham's researches upon colloids, his natural conclusion +was that the agent thus intercepted must be a solid material. In point of +fact, Helmholtz's experiments narrowed the issue to this: that which +excites fermentation and putrefaction, and at the same time gives rise to +living forms in a fermentable or putrescible fluid, is not a gas and is +not a diffusible fluid; therefore it is either a colloid, or it is matter +divided into very minute solid particles. + +The researches of Schroeder and Dusch in 1854, and of Schroeder alone, in +1859, cleared up this point by experiments which are simply refinements +upon those of Redi. A lump of cotton-wool is, physically speaking, a pile +of many thicknesses of a very fine gauze, the fineness of the meshes of +which depends upon the closeness of the compression of the wool. Now, +Schroeder and Dusch found, that, in the case of all the putrefiable +materials which they used (except milk and yolk of egg), an infusion +boiled, and then allowed to come into contact with no air but such as had +been filtered through cotton-wool, neither putrefied, nor fermented, nor +developed living forms. It is hard to imagine what the fine sieve formed +by the cotton-wool could have stopped except minute solid particles. +Still the evidence was incomplete until it had been positively shown, +first, that ordinary air does contain such particles; and, secondly, that +filtration through cotton-wool arrests these particles and allows only +physically pure air to pass. This demonstration has been furnished within +the last year by the remarkable experiments of Professor Tyndall. It has +been a common objection of Abiogenists that, if the doctrine of Biogeny +is true, the air must be thick with germs; and they regard this as the +height of absurdity. But nature occasionally is exceedingly unreasonable, +and Professor Tyndall has proved that this particular absurdity may +nevertheless be a reality. He has demonstrated that ordinary air is no +better than a sort of stirabout of excessively minute solid particles; +that these particles are almost wholly destructible by heat; and that +they are strained off, and the air rendered optically pure, by its being +passed through cotton-wool. + +It remains yet in the order of logic, though not of history, to show that +among these solid destructible particles, there really do exist germs +capable of giving rise to the development of living forms in suitable +menstrua. This piece of work was done by M. Pasteur in those beautiful +researches which will ever render his name famous; and which, in spite of +all attacks upon them, appear to me now, as they did seven years ago,[9] +to be models of accurate experimentation and logical reasoning. He +strained air through cotton-wool, and found, as Schroeder and Dusch had +done, that it contained nothing competent to give rise to the development +of life in fluids highly fitted for that purpose. But the important +further links in the chain of evidence added by Pasteur are three. In the +first place he subjected to microscopic examination the cotton-wool which +had served as strainer, and found that sundry bodies clearly recognisable +as germs, were among the solid particles strained off. Secondly, he +proved that these germs were competent to give rise to living forms by +simply sowing them in a solution fitted for their development. And, +thirdly, he showed that the incapacity of air strained through cotton- +wool to give rise to life, was not due to any occult change effected in +the constituents of the air by the wool, by proving that the cotton-wool +might be dispensed with altogether, and perfectly free access left +between the exterior air and that in the experimental flask. If the neck +of the flask is drawn out into a tube and bent downwards; and if, after +the contained fluid has been carefully boiled, the tube is heated +sufficiently to destroy any germs which may be present in the air which +enters as the fluid cools, the apparatus may be left to itself for any +time and no life will appear in the fluid. The reason is plain. Although +there is free communication between the atmosphere laden with germs and +the germless air in the flask, contact between the two takes place only +in the tube; and as the germs cannot fall upwards, and there are no +currents, they never reach the interior of the flask. But if the tube be +broken short off where it proceeds from the flask, and free access be +thus given to germs falling vertically out of the air, the fluid, which +has remained clear and desert for months, becomes, in a few days, turbid +and full of life. + +[Footnote 9: _Lectures to Working Men on the Causes of the Phenomena of +Organic Nature_, 1863. (See Vol. II. of these Essays.)] + +These experiments have been repeated over and over again by independent +observers with entire success; and there is one very simple mode of +seeing the facts for one's self, which I may as well describe. + +Prepare a solution (much used by M. Pasteur, and often called "Pasteur's +solution") composed of water with tartrate of ammonia, sugar, and yeast- +ash dissolved therein.[10] Divide it into three portions in as many +flasks; boil all three for a quarter of an hour; and, while the steam is +passing out, stop the neck of one with a large plug of cotton-wool, so +that this also may be thoroughly steamed. Now set the flasks aside to +cool, and, when their contents are cold, add to one of the open ones a +drop of filtered infusion of hay which has stood for twenty-four hours, +and is consequently hill of the active and excessively minute organisms +known as _Bacteria_. In a couple of days of ordinary warm weather the +contents of this flask will be milky from the enormous multiplication of +_Bacteria_. The other flask, open and exposed to the air, will, sooner or +later, become milky with _Bacteria_, and patches of mould may appear in +it; while the liquid in the flask, the neck of which is plugged with +cotton-wool, will remain clear for an indefinite time. I have sought in +vain for any explanation of these facts, except the obvious one, that the +air contains germs competent to give rise to _Bacteria_, such as those +with which the first solution has been knowingly and purposely +inoculated, and to the mould-_Fungi_. And I have not yet been able to +meet with any advocate of Abiogenesis who seriously maintains that the +atoms of sugar, tartrate of ammonia, yeast-ash, and water, under no +influence but that of free access of air and the ordinary temperature, +re-arrange themselves and give rise to the protoplasm of _Bacterium_. But +the alternative is to admit that these _Bacteria_ arise from germs in the +air; and if they are thus propagated, the burden of proof that other like +forms are generated in a different manner, must rest with the assertor of +that proposition. + +[Footnote 10: Infusion of hay treated in the same way yields similar +results; but as it contains organic matter, the argument which follows +cannot be based upon it.] + +To sum up the effect of this long chain of evidence:-- + +It is demonstrable that a fluid eminently fit for the development of the +lowest forms of life, but which contains neither germs, nor any protein +compound, gives rise to living things in great abundance if it is exposed +to ordinary air; while no such development takes place, if the air with +which it is in contact is mechanically freed from the solid particles +which ordinarily float in it, and which may be made visible by +appropriate means. + +It is demonstrable that the great majority of these particles are +destructible by heat, and that some of them are germs, or living +particles, capable of giving rise to the same forms of life as those +which appear when the fluid is exposed to unpurified air. + +It is demonstrable that inoculation of the experimental fluid with a drop +of liquid known to contain living particles gives rise to the same +phenomena as exposure to unpurified air. + +And it is further certain that these living particles are so minute that +the assumption of their suspension in ordinary air presents not the +slightest difficulty. On the contrary, considering their lightness and +the wide diffusion of the organisms which produce them, it is impossible +to conceive that they should not be suspended in the atmosphere in +myriads. + +Thus the evidence, direct and indirect, in favour of _Biogenesis_ for all +known forms of life must, I think, be admitted to be of great weight. + +On the other side, the sole assertions worthy of attention are that +hermetically sealed fluids, which have been exposed to great and long- +continued heat, have sometimes exhibited living forms of low organisation +when they have been opened. + +The first reply that suggests itself is the probability that there must +be some error about these experiments, because they are performed on an +enormous scale every day with quite contrary results. Meat, fruits, +vegetables, the very materials of the most fermentable and putrescible +infusions, are preserved to the extent, I suppose I may say, of thousands +of tons every year, by a method which is a mere application of +Spallanzani's experiment. The matters to be preserved are well boiled in +a tin case provided with a small hole, and this hole is soldered up when +all the air in the case has been replaced by steam. By this method they +may be kept for years without putrefying, fermenting, or getting mouldy. +Now this is not because oxygen is excluded, inasmuch as it is now proved +that free oxygen is not necessary for either fermentation or +putrefaction. It is not because the tins are exhausted of air, for +_Vibriones_ and _Bacteria_ live, as Pasteur has shown, without air or +free oxygen. It is not because the boiled meats or vegetables are not +putrescible or fermentable, as those who have had the misfortune to be in +a ship supplied with unskilfully closed tins well know. What is it, +therefore, but the exclusion of germs? I think that Abiogenists are bound +to answer this question before they ask us to consider new experiments of +precisely the same order. + +And in the next place, if the results of the experiments I refer to are +really trustworthy, it by no means follows that Abiogenesis has taken +place. The resistance of living matter to heat is known to vary within +considerable limits, and to depend, to some extent, upon the chemical and +physical qualities of the surrounding medium. But if, in the present +state of science, the alternative is offered us,--either germs can stand +a greater heat than has been supposed, or the molecules of dead matter, +for no valid or intelligible reason that is assigned, are able to re- +arrange themselves into living bodies, exactly such as can be +demonstrated to be frequently produced in another way,--I cannot +understand how choice can be, even for a moment, doubtful. + +But though I cannot express this conviction of mine too strongly, I must +carefully guard myself against the supposition that I intend to suggest +that no such thing as Abiogenesis ever has taken place in the past, or +ever will take place in the future. With organic chemistry, molecular +physics, and physiology yet in their infancy, and every day making +prodigious strides, I think it would be the height of presumption for any +man to say that the conditions under which matter assumes the properties +we call "vital" may not, some day, be artificially brought together. All +I feel justified in affirming is, that I see no reason for believing that +the feat has been performed yet. + +And looking back through the prodigious vista of the past, I find no +record of the commencement of life, and therefore I am devoid of any +means of forming a definite conclusion as to the conditions of its +appearance. Belief, in the scientific sense of the word, is a serious +matter, and needs strong foundations. To say, therefore, in the admitted +absence of evidence, that I have any belief as to the mode in which the +existing forms of life have originated, would be using words in a wrong +sense. But expectation is permissible where belief is not; and if it were +given me to look beyond the abyss of geologically recorded time to the +still more remote period when the earth was passing through physical and +chemical conditions, which it can no more see again than a man can recall +his infancy, I should expect to be a witness of the evolution of living +protoplasm from not living matter. I should expect to see it appear under +forms of great simplicity, endowed, like existing fungi, with the power +of determining the formation of new protoplasm from such matters as +ammonium carbonates, oxalates and tartrates, alkaline and earthy +phosphates, and water, without the aid of light. That is the expectation +to which analogical reasoning leads me; but I beg you once more to +recollect that I have no right to call my opinion anything but an act of +philosophical faith. + +So much for the history of the progress of Redi's great doctrine of +Biogenesis, which appears to me, with the limitations I have expressed, +to be victorious along the whole line at the present day. + +As regards the second problem offered to us by Redi, whether Xenogenesis +obtains, side by side with Homogenesis,--whether, that is, there exist +not only the ordinary living things, giving rise to offspring which run +through the same cycle as themselves, but also others, producing +offspring which are of a totally different character from themselves,-- +the researches of two centuries have led to a different result. That the +grubs found in galls are no product of the plants on which the galls +grow, but are the result of the introduction of the eggs of insects into +the substance of these plants, was made out by Vallisnieri, Reaumur, and +others, before the end of the first half of the eighteenth century. The +tapeworms, bladderworms, and flukes continued to be a stronghold of the +advocates of Xenogenesis for a much longer period. Indeed, it is only +within the last thirty years that the splendid patience of Von Siebold, +Van Beneden, Leuckart, Kuechenmeister, and other helminthologists, has +succeeded in tracing every such parasite, often through the strangest +wanderings and metamorphoses, to an egg derived from a parent, actually +or potentially like itself; and the tendency of inquiries elsewhere has +all been in the same direction. A plant may throw off bulbs, but these, +sooner or later, give rise to seeds or spores, which develop into the +original form. A polype may give rise to Medusae, or a pluteus to an +Echinoderm, but the Medusa and the Echinoderm give rise to eggs which +produce polypes or glutei, and they are therefore only stages in the +cycle of life of the species. + +But if we turn to pathology, it offers us some remarkable approximations +to true Xenogenesis. + +As I have already mentioned, it has been known since the time of +Vallisnieri and of Reaumur, that galls in plants, and tumours in cattle, +are caused by insects, which lay their eggs in those parts of the animal +or vegetable frame of which these morbid structures are outgrowths. +Again, it is a matter of familiar experience to everybody that mere +pressure on the skin will give rise to a corn. Now the gall, the tumour, +and the corn are parts of the living body, which have become, to a +certain degree, independent and distinct organisms. Under the influence +of certain external conditions, elements of the body, which should have +developed in due subordination to its general plan, set up for themselves +and apply the nourishment which they receive to their own purposes. + +From such innocent productions as corns and warts, there are all +gradations to the serious tumours which, by their mere size and the +mechanical obstruction they cause, destroy the organism out of which they +are developed; while, finally, in those terrible structures known as +cancers, the abnormal growth has acquired powers of reproduction and +multiplication, and is only morphologically distinguishable from the +parasitic worm, the life of which is neither more nor less closely bound +up with that of the infested organism. + +If there were a kind of diseased structure, the histological elements of +which were capable of maintaining a separate and independent existence +out of the body, it seems to me that the shadowy boundary between morbid +growth and Xenogenesis would be effaced. And I am inclined to think that +the progress of discovery has almost brought us to this point already. I +have been favoured by Mr. Simon with an early copy of the last published +of the valuable "Reports on the Public Health," which, in his capacity of +their medical officer, he annually presents to the Lords of the Privy +Council. The appendix to this report contains an introductory essay "On +the Intimate Pathology of Contagion," by Dr. Burdon-Sanderson, which is +one of the clearest, most comprehensive, and well-reasoned discussions of +a great question which has come under my notice for a long time. I refer +you to it for details and for the authorities for the statements I am +about to make. + +You are familiar with what happens in vaccination. A minute cut is made +in the skin, and an infinitesimal quantity of vaccine matter is inserted +into the wound. Within a certain time a vesicle appears in the place of +the wound, and the fluid which distends this vesicle is vaccine matter, +in quantity a hundred or a thousandfold that which was originally +inserted. Now what has taken place in the course of this operation? Has +the vaccine matter, by its irritative property, produced a mere blister, +the fluid of which has the same irritative property? Or does the vaccine +matter contain living particles, which have grown and multiplied where +they have been planted? The observations of M. Chauveau, extended and +confirmed by Dr. Sanderson himself, appear to leave no doubt upon this +head. Experiments, similar in principle to those of Helmholtz on +fermentation and putrefaction, have proved that the active element in the +vaccine lymph is non-diffusible, and consists of minute particles not +exceeding 1/20000th of an inch in diameter, which are made visible in the +lymph by the microscope. Similar experiments have proved that two of the +most destructive of epizootic diseases, sheep-pox and glanders, are also +dependent for their existence and their propagation upon extremely small +living solid particles, to which the title of _microzymes_ is applied. An +animal suffering under either of these terrible diseases is a source of +infection and contagion to others, for precisely the same reason as a tub +of fermenting beer is capable of propagating its fermentation by +"infection," or "contagion," to fresh wort. In both cases it is the solid +living particles which are efficient; the liquid in which they float, and +at the expense of which they live, being altogether passive. + +Now arises the question, are these microzymes the results of +_Homogenesis_, or of _Xenogenesis?_ are they capable, like the +_Toruloe_ of yeast, of arising only by the development of pre-existing +germs? or may they be, like the constituents of a nut-gall, the results +of a modification and individualisation of the tissues of the body in +which they are found, resulting from the operation of certain conditions? +Are they parasites in the zoological sense, or are they merely what +Virchow has called "heterologous growths"? It is obvious that this +question has the most profound importance, whether we look at it from a +practical or from a theoretical point of view. A parasite may be stamped +out by destroying its germs, but a pathological product can only be +annihilated by removing the conditions which give rise to it. + +It appears to me that this great problem will have to be solved for each +zymotic disease separately, for analogy cuts two ways. I have dwelt upon +the analogy of pathological modification, which is in favour of the +xenogenetic origin of microzymes; but I must now speak of the equally +strong analogies in favour of the origin of such pestiferous particles by +the ordinary process of the generation of like from like. + +It is, at present, a well-established fact that certain diseases, both of +plants and of animals, which have all the characters of contagious and +infectious epidemics, are caused by minute organisms. The smut of wheat +is a well-known instance of such a disease, and it cannot be doubted that +the grape-disease and the potato-disease fall under the same category. +Among animals, insects are wonderfully liable to the ravages of +contagious and infectious diseases caused by microscopic _Fungi_. + +In autumn, it is not uncommon to see flies motionless upon a window-pane, +with a sort of magic circle, in white, drawn round them. On microscopic +examination, the magic circle is found to consist of innumerable spores, +which have been thrown off in all directions by a minute fungus called +_Empusa muscoe_, the spore-forming filaments of which stand out like a +pile of velvet from the body of the fly. These spore-forming filaments +are connected with others which fill the interior of the fly's body like +so much fine wool, having eaten away and destroyed the creature's +viscera. This is the full-grown condition of the _Empusa_. If traced back +to its earliest stages, in flies which are still active, and to all +appearance healthy, it is found to exist in the form of minute corpuscles +which float in the blood of the fly. These multiply and lengthen into +filaments, at the expense of the fly's substance; and when they have at +last killed the patient, they grow out of its body and give off spores. +Healthy flies shut up with diseased ones catch this mortal disease, and +perish like the others. A most competent observer, M. Cohn, who studied +the development of the _Empusa_ very carefully, was utterly unable to +discover in what manner the smallest germs of the _Empusa_ got into the +fly. The spores could not be made to give rise to such germs by +cultivation; nor were such germs discoverable in the air, or in the food +of the fly. It looked exceedingly like a case of Abiogenesis, or, at any +rate, of Xenogenesis; and it is only quite recently that the real course +of events has been made out. It has been ascertained, that when one of +the spores falls upon the body of a fly, it begins to germinate, and +sends out a process which bores its way through the fly's skin; this, +having reached the interior cavities of its body, gives off the minute +floating corpuscles which are the earliest stage of the _Empusa_. The +disease is "contagious," because a healthy fly coming in contact with a +diseased one, from which the spore-bearing filaments protrude, is pretty +sure to carry off a spore or two. It is "infectious" because the spores +become scattered about all sorts of matter in the neighbourhood of the +slain flies. + +The silkworm has long been known to be subject to a very fatal and +infectious disease called the _Muscardine_. Audouin transmitted it by +inoculation. This disease is entirely due to the development of a fungus, +_Botrytis Bassiana_, in the body of the caterpillar; and its +contagiousness and infectiousness are accounted for in the same way as +those of the fly-disease. But, of late years, a still more serious +epizootic has appeared among the silkworms; and I may mention a few facts +which will give you some conception of the gravity of the injury which it +has inflicted on France alone. + +The production of silk has been for centuries an important branch of +industry in Southern France, and in the year 1853 it had attained such a +magnitude that the annual produce of the French sericulture was estimated +to amount to a tenth of that of the whole world, and represented a money- +value of 117,000,000 francs, or nearly five millions sterling. What may +be the sum which would represent the money-value of all the industries +connected with the working up of the raw silk thus produced, is more than +I can pretend to estimate. Suffice it to say, that the city of Lyons is +built upon French silk as much as Manchester was upon American cotton +before the civil war. + +Silkworms are liable to many diseases; and, even before 1853, a peculiar +epizootic, frequently accompanied by the appearance of dark spots upon +the skin (whence the name of "Pebrine" which it has received), had been +noted for its mortality. But in the years following 1853 this malady +broke out with such extreme violence, that, in 1858, the silk-crop was +reduced to a third of the amount which it had reached in 1853; and, up +till within the last year or two, it has never attained half the yield of +1853. This means not only that the great number of people engaged in silk +growing are some thirty millions sterling poorer than they might have +been; it means not only that high prices have had to be paid for imported +silkworm eggs, and that, after investing his money in them, in paying for +mulberry-leaves and for attendance, the cultivator has constantly seen +his silkworms perish and himself plunged in ruin; but it means that the +looms of Lyons have lacked employment, and that, for years, enforced +idleness and misery have been the portion of a vast population which, in +former days, was industrious and well-to-do. + +In 1858 the gravity of the situation caused the French Academy of +Sciences to appoint Commissioners, of whom a distinguished naturalist, M. +de Quatrefages, was one, to inquire into the nature of this disease, and, +if possible, to devise some means of staying the plague. In reading the +Report[11] made by M. de Quatrefages in 1859, it is exceedingly +interesting to observe that his elaborate study of the Pebrine forced the +conviction upon his mind that, in its mode of occurrence and propagation, +the disease of the silkworm is, in every respect, comparable to the +cholera among mankind. But it differs from the cholera, and so far is a +more formidable malady, in being hereditary, and in being, under some +circumstances, contagious as well as infectious. + +[Footnote 11: _Etudes sur les Maladies actuelles des Vers a Soie_, p. +53.] + +The Italian naturalist, Filippi, discovered in the blood of the silkworms +affected by this strange disorder a multitude of cylindrical corpuscles, +each about 1/6000th of an inch long. These have been carefully studied by +Lebert, and named by him _Panhistophyton_; for the reason that in +subjects in which the disease is strongly developed, the corpuscles swarm +in every tissue and organ of the body, and even pass into the undeveloped +eggs of the female moth. But are these corpuscles causes, or mere +concomitants, of the disease? Some naturalists took one view and some +another; and it was not until the French Government, alarmed by the +continued ravages of the malady, and the inefficiency of the remedies +which had been suggested, despatched M. Pasteur to study it, that the +question received its final settlement; at a great sacrifice, not only of +the time and peace of mind of that eminent philosopher, but, I regret to +have to add, of his health. + +But the sacrifice has not been in vain. It is now certain that this +devastating, cholera-like, Pebrine, is the effect of the growth and +multiplication of the _Panhistophyton_ in the silkworm. It is contagious +and infectious, because the corpuscles of the _Panhistophyton_ pass away +from the bodies of the diseased caterpillars, directly or indirectly, to +the alimentary canal of healthy silkworms in their neighbourhood; it is +hereditary because the corpuscles enter into the eggs while they are +being formed, and consequently are carried within them when they are +laid; and for this reason, also, it presents the very singular +peculiarity of being inherited only on the mother's side. There is not a +single one of all the apparently capricious and unaccountable phenomena +presented by the Pebrine, but has received its explanation from the fact +that the disease is the result of the presence of the microscopic +organism, _Panhistophyton_. + +Such being the facts with respect to the Pebrine, what are the +indications as to the method of preventing it? It is obvious that this +depends upon the way in which the _Panhistophyton_ is generated. If it +may be generated by Abiogenesis, or by Xenogenesis, within the silkworm +or its moth, the extirpation of the disease must depend upon the +prevention of the occurrence of the conditions under which this +generation takes place. But if, on the other hand, the _Panhistophyton_ +is an independent organism, which is no more generated by the silkworm +than the mistletoe is generated by the apple-tree or the oak on which it +grows, though it may need the silkworm for its development in the same +way as the mistletoe needs the tree, then the indications are totally +different. The sole thing to be done is to get rid of and keep away the +germs of the _Panhistophyton_. As might be imagined, from the course of +his previous investigations, M. Pasteur was led to believe that the +latter was the right theory; and, guided by that theory, he has devised a +method of extirpating the disease, which has proved to be completely +successful wherever it has been properly carried out. + +There can be no reason, then, for doubting that, among insects, +contagious and infectious diseases, of great malignity, are caused by +minute organisms which are produced from pre-existing germs, or by +homogenesis; and there is no reason, that I know of, for believing that +what happens in insects may not take place in the highest animals. +Indeed, there is already strong evidence that some diseases of an +extremely malignant and fatal character to which man is subject, are as +much the work of minute organisms as is the Pebrine. I refer for this +evidence to the very striking facts adduced by Professor Lister in his +various well-known publications on the antiseptic method of treatment. It +appears to me impossible to rise from the perusal of those publications +without a strong conviction that the lamentable mortality which so +frequently dogs the footsteps of the most skilful operator, and those +deadly consequences of wounds and injuries which seem to haunt the very +walls of great hospitals, and are, even now, destroying more men than die +of bullet or bayonet, are due to the importation of minute organisms into +wounds, and their increase and multiplication; and that the surgeon who +saves most lives will be he who best works out the practical consequences +of the hypothesis of Redi. + +I commenced this Address by asking you to follow me in an attempt to +trace the path which has been followed by a scientific idea, in its long +and slow progress from the position of a probable hypothesis to that of +an established law of nature. Our survey has not taken us into very +attractive regions; it has lain, chiefly, in a land flowing with the +abominable, and peopled with mere grubs and mouldiness. And it may be +imagined with what smiles and shrugs, practical and serious +contemporaries of Redi and of Spallanzani may have commented on the waste +of their high abilities in toiling at the solution of problems which, +though curious enough in themselves, could be of no conceivable utility +to mankind. + +Nevertheless, you will have observed that before we had travelled very +far upon our road, there appeared, on the right hand and on the left, +fields laden with a harvest of golden grain, immediately convertible into +those things which the most solidly practical men will admit to have +value--viz., money and life. + +The direct loss to France caused by the Pebrine in seventeen years cannot +be estimated at less than fifty millions sterling; and if we add to this +what Redi's idea, in Pasteur's hands, has done for the wine-grower and +for the vinegar-maker, and try to capitalise its value, we shall find +that it will go a long way towards repairing the money losses caused by +the frightful and calamitous war of this autumn. And as to the equivalent +of Redi's thought in life, how can we over-estimate the value of that +knowledge of the nature of epidemic and epizootic diseases, and +consequently of the means of checking, or eradicating them, the dawn of +which has assuredly commenced? + +Looking back no further than ten years, it is possible to select three +(1863, 1864, and 1869) in which the total number of deaths from scarlet- +fever alone amounted to ninety thousand. That is the return of killed, +the maimed and disabled being left out of sight. Why, it is to be hoped +that the list of killed in the present bloodiest of all wars will not +amount to more than this! But the facts which I have placed before you +must leave the least sanguine without a doubt that the nature and the +causes of this scourge will, one day, be as well understood as those of +the Pebrine are now; and that the long-suffered massacre of our innocents +will come to an end. + +And thus mankind will have one more admonition that "the people perish +for lack of knowledge"; and that the alleviation of the miseries, and the +promotion of the welfare, of men must be sought, by those who will not +lose their pains, in that diligent, patient, loving study of all the +multitudinous aspects of Nature, the results of which constitute exact +knowledge, or Science. It is the justification and the glory of this +great meeting that it is gathered together for no other object than the +advancement of the moiety of science which deals with those phenomena of +nature which we call physical. May its endeavours be crowned with a full +measure of success! + + + +IX + + +GEOLOGICAL CONTEMPORANEITY AND PERSISTENT TYPES OF LIFE + +[1862] + +Merchants occasionally go through a wholesome, though troublesome and not +always satisfactory, process which they term "taking stock." After all +the excitement of speculation, the pleasure of gain, and the pain of +loss, the trader makes up his mind to face facts and to learn the exact +quantity and quality of his solid and reliable possessions. + +The man of science does well sometimes to imitate this procedure; and, +forgetting for the time the importance of his own small winnings, to re- +examine the common stock in trade, so that he may make sure how far the +stock of bullion in the cellar--on the faith of whose existence so much +paper has been circulating--is really the solid gold of truth. + +The Anniversary Meeting of the Geological Society seems to be an occasion +well suited for an undertaking of this kind--for an inquiry, in fact, +into the nature and value of the present results of palaeontological +investigation; and the more so, as all those who have paid close +attention to the late multitudinous discussions in which palaeontology is +implicated, must have felt the urgent necessity of some such scrutiny. + +First in order, as the most definite and unquestionable of all the +results of palaeontology, must be mentioned the immense extension and +impulse given to botany, zoology, and comparative anatomy, by the +investigation of fossil remains. Indeed, the mass of biological facts has +been so greatly increased, and the range of biological speculation has +been so vastly widened, by the researches of the geologist and +palaeontologist, that it is to be feared there are naturalists in +existence who look upon geology as Brindley regarded rivers. "Rivers," +said the great engineer, "were made to feed canals;" and geology, some +seem to think, was solely created to advance comparative anatomy. + +Were such a thought justifiable, it could hardly expect to be received +with favour by this assembly. But it is not justifiable. Your favourite +science has her own great aims independent of all others; and if, +notwithstanding her steady devotion to her own progress, she can scatter +such rich alms among her sisters, it should be remembered that her +charity is of the sort that does not impoverish, but "blesseth him that +gives and him that takes." + +Regard the matter as we will, however, the facts remain. Nearly 40,000 +species of animals and plants have been added to the Systema Naturae by +palaeontological research. This is a living population equivalent to that +of a new continent in mere number; equivalent to that of a new +hemisphere, if we take into account the small population of insects as +yet found fossil, and the large proportion and peculiar organisation of +many of the Vertebrata. + +But, beyond this, it is perhaps not too much to say that, except for the +necessity of interpreting palaeontological facts, the laws of distribution +would have received less careful study; while few comparative anatomists +(and those not of the first order) would have been induced by mere love +of detail, as such, to study the minutiae of osteology, were it not that +in such minutiae lie the only keys to the most interesting riddles offered +by the extinct animal world. + +These assuredly are great and solid gains. Surely it is matter for no +small congratulation that in half a century (for palaeontology, though it +dawned earlier, came into full day only with Cuvier) a subordinate branch +of biology should have doubled the value and the interest of the whole +group of sciences to which it belongs. + +But this is not all. Allied with geology, palaeontology has established +two laws of inestimable importance: the first, that one and the same area +of the earth's surface has been successively occupied by very different +kinds of living beings; the second, that the order of succession +established in one locality holds good, approximately, in all. + +The first of these laws is universal and irreversible; the second is an +induction from a vast number of observations, though it may possibly, and +even probably, have to admit of exceptions. As a consequence of the +second law, it follows that a peculiar relation frequently subsists +between series of strata containing organic remains, in different +localities. The series resemble one another not only in virtue of a +general resemblance of the organic remains in the two, but also in virtue +of a resemblance in the order and character of the serial succession in +each. There is a resemblance of arrangement; so that the separate terms +of each series, as well as the whole series, exhibit a correspondence. + +Succession implies time; the lower members of an undisturbed series of +sedimentary rocks are certainly older than the upper; and when the notion +of age was once introduced as the equivalent of succession, it was no +wonder that correspondence in succession came to be looked upon as a +correspondence in age, or "contemporaneity." And, indeed, so long as +relative age only is spoken of, correspondence in succession _is_ +correspondence in age; it is _relative_ contemporaneity. + +But it would have been very much better for geology if so loose and +ambiguous a word as "contemporaneous" had been excluded from her +terminology, and if, in its stead, some term expressing similarity of +serial relation, and excluding the notion of time altogether, had been +employed to denote correspondence in position in two or more series of +strata. + +In anatomy, where such correspondence of position has constantly to be +spoken of, it is denoted by the word "homology" and its derivatives; and +for Geology (which after all is only the anatomy and physiology of the +earth) it might be well to invent some single word, such as "homotaxis" +(similarity of order), in order to express an essentially similar idea. +This, however, has not been done, and most probably the inquiry will at +once be made--To what end burden science with a new and strange term in +place of one old, familiar, and part of our common language? + +The reply to this question will become obvious as the inquiry into the +results of palaeontology is pushed further. + +Those whose business it is to acquaint themselves specially with the +works of palaeontologists, in fact, will be fully aware that very few, if +any, would rest satisfied with such a statement of the conclusions of +their branch of biology as that which has just been given. + +Our standard repertories of palaeontology profess to teach us far higher +things--to disclose the entire succession of living forms upon the +surface of the globe; to tell us of a wholly different distribution of +climatic conditions in ancient times; to reveal the character of the +first of all living existences; and to trace out the law of progress from +them to us. + +It may not be unprofitable to bestow on these professions a somewhat more +critical examination than they have hitherto received, in order to +ascertain how far they rest on an irrefragable basis; or whether, after +all, it might not be well for palaeontologists to learn a little more +carefully that scientific "ars artium," the art of saying "I don't know." +And to this end let us define somewhat more exactly the extent of these +pretensions of palaeontology. + +Every one is aware that Professor Bronn's "Untersuchungen" and Professor +Pictet's "Traite de Paleontologie" are works of standard authority, +familiarly consulted by every working palaeontologist. It is desirable to +speak of these excellent books, and of their distinguished authors, with +the utmost respect, and in a tone as far as possible removed from carping +criticism; indeed, if they are specially cited in this place, it is +merely in justification of the assertion that the following propositions, +which may be found implicitly, or explicitly, in the works in question, +are regarded by the mass of palaeontologists and geologists, not only on +the Continent but in this country, as expressing some of the best- +established results of palaeontology. Thus:-- + +Animals and plants began their existence together, not long after the +commencement of the deposition of the sedimentary rocks; and then +succeeded one another, in such a manner, that totally distinct faunae and +florae occupied the whole surface of the earth, one after the other, and +during distinct epochs of time. + +A geological formation is the sum of all the strata deposited over the +whole surface of the earth during one of these epochs: a geological fauna +or flora is the sum of all the species of animals or plants which +occupied the whole surface of the globe, during one of these epochs. + +The population of the earth's surface was at first very similar in all +parts, and only from the middle of the Tertiary epoch onwards, began to +show a distinct distribution in zones. + +The constitution of the original population, as well as the numerical +proportions of its members, indicates a warmer and, on the whole, +somewhat tropical climate, which remained tolerably equable throughout +the year. The subsequent distribution of living beings in zones is the +result of a gradual lowering of the general temperature, which first +began to be felt at the poles. + +It is not now proposed to inquire whether these doctrines are true or +false; but to direct your attention to a much simpler though very +essential preliminary question--What is their logical basis? what are the +fundamental assumptions upon which they all logically depend? and what is +the evidence on which those fundamental propositions demand our assent? + +These assumptions are two: the first, that the commencement of the +geological record is coeval with the commencement of life on the globe; +the second, that geological contemporaneity is the same thing as +chronological synchrony. Without the first of these assumptions there +would of course be no ground for any statement respecting the +commencement of life; without the second, all the other statements cited, +every one of which implies a knowledge of the state of different parts of +the earth at one and the same time, will be no less devoid of +demonstration. + +The first assumption obviously rests entirely on negative evidence. This +is, of course, the only evidence that ever can be available to prove the +commencement of any series of phenomena; but, at the same time, it must +be recollected that the value of negative evidence depends entirely on +the amount of positive corroboration it receives. If A.B. wishes to prove +an _alibi_, it is of no use for him to get a thousand witnesses simply to +swear that they did not see him in such and such a place, unless the +witnesses are prepared to prove that they must have seen him had he been +there. But the evidence that animal life commenced with the Lingula- +flags, _e.g._, would seem to be exactly of this unsatisfactory +uncorroborated sort. The Cambrian witnesses simply swear they "haven't +seen anybody their way"; upon which the counsel for the other side +immediately puts in ten or twelve thousand feet of Devonian sandstones to +make oath they never saw a fish or a mollusk, though all the world knows +there were plenty in their time. + +But then it is urged that, though the Devonian rocks in one part of the +world exhibit no fossils, in another they do, while the lower Cambrian +rocks nowhere exhibit fossils, and hence no living being could have +existed in their epoch. + +To this there are two replies: the first that the observational basis of +the assertion that the lowest rocks are nowhere fossiliferous is an +amazingly small one, seeing how very small an area, in comparison to that +of the whole world, has yet been fully searched; the second, that the +argument is good for nothing unless the unfossiliferous rocks in question +were not only _contemporaneous_ in the geological sense, but +_synchronous_ in the chronological sense. To use the _alibi_ illustration +again. If a man wishes to prove he was in neither of two places, A and B, +on a given day, his witnesses for each place must be prepared to answer +for the whole day. If they can only prove that he was not at A in the +morning, and not at B in the afternoon, the evidence of his absence from +both is nil, because he might have been at B in the morning and at A in +the afternoon. + +Thus everything depends upon the validity of the second assumption. And +we must proceed to inquire what is the real meaning of the word +"contemporaneous" as employed by geologists. To this end a concrete +example may be taken. + +The Lias of England and the Lias of Germany, the Cretaceous rocks of +Britain and the Cretaceous rocks of Southern India, are termed by +geologists "contemporaneous" formations; but whenever any thoughtful +geologist is asked whether he means to say that they were deposited +synchronously, he says, "No,--only within the same great epoch." And if, +in pursuing the inquiry, he is asked what may be the approximate value in +time of a "great epoch"--whether it means a hundred years, or a thousand, +or a million, or ten million years--his reply is, "I cannot tell." + +If the further question be put, whether physical geology is in possession +of any method by which the actual synchrony (or the reverse) of any two +distant deposits can be ascertained, no such method can be heard of; it +being admitted by all the best authorities that neither similarity of +mineral composition, nor of physical character, nor even direct +continuity of stratum, are _absolute_ proofs of the synchronism of even +approximated sedimentary strata: while, for distant deposits, there seems +to be no kind of physical evidence attainable of a nature competent to +decide whether such deposits were formed simultaneously, or whether they +possess any given difference of antiquity. To return to an example +already given: All competent authorities will probably assent to the +proposition that physical geology does not enable us in any way to reply +to this question--Were the British Cretaceous rocks deposited at the same +time as those of India, or are they a million of years younger or a +million of years older? + +Is palaeontology able to succeed where physical geology fails? Standard +writers on palaeontology, as has been seen, assume that she can. They take +it for granted, that deposits containing similar organic remains are +synchronous--at any rate in a broad sense; and yet, those who will study +the eleventh and twelfth chapters of Sir Henry De La Beche's remarkable +"Researches in Theoretical Geology," published now nearly thirty years +ago, and will carry out the arguments there most luminously stated, to +their logical consequences, may very easily convince themselves that even +absolute identity of organic contents is no proof of the synchrony of +deposits, while absolute diversity is no proof of difference of date. Sir +Henry De La Beche goes even further, and adduces conclusive evidence to +show that the different parts of one and the same stratum, having a +similar composition throughout, containing the same organic remains, and +having similar beds above and below it, may yet differ to any conceivable +extent in age. + +Edward Forbes was in the habit of asserting that the similarity of the +organic contents of distant formations was _prima facie_ evidence, not of +their similarity, but of their difference of age; and holding as he did +the doctrine of single specific centres, the conclusion was as legitimate +as any other; for the two districts must have been occupied by migration +from one of the two, or from an intermediate spot, and the chances +against exact coincidence of migration and of imbedding are infinite. + +In point of fact, however, whether the hypothesis of single or of +multiple specific centres be adopted, similarity of organic contents +cannot possibly afford any proof of the synchrony of the deposits which +contain them; on the contrary, it is demonstrably compatible with the +lapse of the most prodigious intervals of time, and with the +interposition of vast changes in the organic and inorganic worlds, +between the epochs in which such deposits were formed. + +On what amount of similarity of their faunae is the doctrine of the +contemporaneity of the European and of the North American Silurians +based? In the last edition of Sir Charles Lyell's "Elementary Geology" it +is stated, on the authority of a former President of this Society, the +late Daniel Sharpe, that between 30 and 40 per cent. of the species of +Silurian Mollusca are common to both sides of the Atlantic. By way of due +allowance for further discovery, let us double the lesser number and +suppose that 60 per cent. of the species are common to the North American +and the British Silurians. Sixty per cent. of species in common is, then, +proof of contemporaneity. + +Now suppose that, a million or two of years hence, when Britain has made +another dip beneath the sea and has come up again, some geologist applies +this doctrine, in comparing the strata laid bare by the upheaval of the +bottom, say, of St. George's Channel with what may then remain of the +Suffolk Crag. Reasoning in the same way, he will at once decide the +Suffolk Crag and the St. George's Channel beds to be contemporaneous; +although we happen to know that a vast period (even in the geological +sense) of time, and physical changes of almost unprecedented extent, +separate the two. But if it be a demonstrable fact that strata +containing more than 60 or 70 per cent. of species of Mollusca in common, +and comparatively close together, may yet be separated by an amount of +geological time sufficient to allow of some of the greatest physical +changes the world has seen, what becomes of that sort of contemporaneity +the sole evidence of which is a similarity of facies, or the identity of +half a dozen species, or of a good many genera? + +And yet there is no better evidence for the contemporaneity assumed by +all who adopt the hypothesis of universal faunae and florae, of a +universally uniform climate, and of a sensible cooling of the globe +during geological time. + +There seems, then, no escape from the admission that neither physical +geology, nor palaeontology, possesses any method by which the absolute +synchronism of two strata can be demonstrated. All that geology can prove +is local order of succession. It is mathematically certain that, in any +given vertical linear section of an undisturbed series of sedimentary +deposits, the bed which lies lowest is the oldest. In many other vertical +linear sections of the same series, of course, corresponding beds will +occur in a similar order; but, however great may be the probability, no +man can say with absolute certainty that the beds in the two sections +were synchronously deposited. For areas of moderate extent, it is +doubtless true that no practical evil is likely to result from assuming +the corresponding beds to be synchronous or strictly contemporaneous; and +there are multitudes of accessory circumstances which may fully justify +the assumption of such synchrony. But the moment the geologist has to +deal with large areas, or with completely separated deposits, the +mischief of confounding that "homotaxis" or "similarity of arrangement," +which _can_ be demonstrated, with "synchrony" or "identity of date," for +which there is not a shadow of proof, under the one common term of +"contemporaneity" becomes incalculable, and proves the constant source of +gratuitous speculations. + +For anything that geology or palaeontology are able to show to the +contrary, a Devonian fauna and flora in the British Islands may have been +contemporaneous with Silurian life in North America, and with a +Carboniferous fauna and flora in Africa. Geographical provinces and zones +may have been as distinctly marked in the Palaeozoic epoch as at present, +and those seemingly sudden appearances of new genera and species, which +we ascribe to new creation, may be simple results of migration. + +It may be so; it may be otherwise. In the present condition of our +knowledge and of our methods, one verdict--"not proven, and not +provable"--must be recorded against all the grand hypotheses of the +palaeontologist respecting the general succession of life on the globe. +The order and nature of terrestrial life, as a whole, are open questions. +Geology at present provides us with most valuable topographical records, +but she has not the means of working them into a universal history. Is +such a universal history, then, to be regarded as unattainable? Are all +the grandest and most interesting problems which offer themselves to the +geological student, essentially insoluble? Is he in the position of a +scientific Tantalus--doomed always to thirst for a knowledge which he +cannot obtain? The reverse is to be hoped; nay, it may not be impossible +to indicate the source whence help will come. + +In commencing these remarks, mention was made of the great obligations +under which the naturalist lies to the geologist and palaeontologist. +Assuredly the time will come when these obligations will be repaid +tenfold, and when the maze of the world's past history, through which the +pure geologist and the pure palaeontologist find no guidance, will be +securely threaded by the clue furnished by the naturalist. + +All who are competent to express an opinion on the subject are, at +present, agreed that the manifold varieties of animal and vegetable form +have not either come into existence by chance, nor result from capricious +exertions of creative power; but that they have taken place in a definite +order, the statement of which order is what men of science term a natural +law. Whether such a law is to be regarded as an expression of the mode of +operation of natural forces, or whether it is simply a statement of the +manner in which a supernatural power has thought fit to act, is a +secondary question, so long as the existence of the law and the +possibility of its discovery by the human intellect are granted. But he +must be a half-hearted philosopher who, believing in that possibility, +and having watched the gigantic strides of the biological sciences during +the last twenty years, doubts that science will sooner or later make this +further step, so as to become possessed of the law of evolution of +organic forms--of the unvarying order of that great chain of causes and +effects of which all organic forms, ancient and modern, are the links. +And then, if ever, we shall be able to begin to discuss, with profit, the +questions respecting the commencement of life, and the nature of the +successive populations of the globe, which so many seem to think are +already answered. + +The preceding arguments make no particular claim to novelty; indeed they +have been floating more or less distinctly before the minds of geologists +for the last thirty years; and if, at the present time, it has seemed +desirable to give them more definite and systematic expression, it is +because palaeontology is every day assuming a greater importance, and now +requires to rest on a basis the firmness of which is thoroughly well +assured. Among its fundamental conceptions, there must be no confusion +between what is certain and what is more or less probable.[1] But, +pending the construction of a surer foundation than palaeontology now +possesses, it may be instructive, assuming for the nonce the general +correctness of the ordinary hypothesis of geological contemporaneity, to +consider whether the deductions which are ordinarily drawn from the whole +body of palaeontological facts are justifiable. + +[Footnote 1: "Le plus grand service qu'on puisse rendre a la science est +d'y faire place nette avant d'y rien construire."--CUVIER.] + +The evidence on which such conclusions are based is of two kinds, +negative and positive. The value of negative evidence, in connection with +this inquiry, has been so fully and clearly discussed in an address from +the chair of this Society,[2] which none of us have forgotten, that +nothing need at present be said about it; the more, as the considerations +which have been laid before you have certainly not tended to increase +your estimation of such evidence. It will be preferable to turn to the +positive facts of palaeontology, and to inquire what they tell us. + +[Footnote 2: Anniversary Address for 1851, _Quart. Journ. Geol. Soc._ +vol. vii.] + +We are all accustomed to speak of the number and the extent of the +changes in the living population of the globe during geological time as +something enormous: and indeed they are so, if we regard only the +negative differences which separate the older rocks from the more modern, +and if we look upon specific and generic changes as great changes, which +from one point of view, they truly are. But leaving the negative +differences out of consideration, and looking only at the positive data +furnished by the fossil world from a broader point of view--from that of +the comparative anatomist who has made the study of the greater +modifications of animal form his chief business--a surprise of another +kind dawns upon the mind; and under _this_ aspect the smallness of the +total change becomes as astonishing as was its greatness under the other. + +There are two hundred known orders of plants; of these not one is +certainly known to exist exclusively in the fossil state. The whole lapse +of geological time has as yet yielded not a single new ordinal type of +vegetable structure.[3] + +[Footnote 3: See Hooker's _Introductory Essay to the Flora of Tasmania_, +p. xxiii.] + +The positive change in passing from the recent to the ancient animal +world is greater, but still singularly small. No fossil animal is so +distinct from those now living as to require to be arranged even in a +separate class from those which contain existing forms. It is only when +we come to the orders, which may be roughly estimated at about a hundred +and thirty, that we meet with fossil animals so distinct from those now +living as to require orders for themselves; and these do not amount, on +the most liberal estimate, to more than about 10 per cent. of the whole. + +There is no certainly known extinct order of Protozoa; there is but one +among the Coelenterata--that of the rugose corals; there is none among +the Mollusca; there are three, the Cystidea, Blastoidea, and +Edrioasterida, among the Echinoderms; and two, the Trilobita and +Eurypterida, among the Crustacea; making altogether five for the great +sub-kingdom of Annulosa. Among Vertebrates there is no ordinally distinct +fossil fish: there is only one extinct order of Amphibia--the +Labyrinthodonts; but there are at least four distinct orders of Reptilia, +viz. the Ichthyosauria, Plesiosauria, Pterosauria, Dinosauria, and +perhaps another or two. There is no known extinct order of Birds, and no +certainly known extinct order of Mammals, the ordinal distinctness of the +"Toxodontia" being doubtful. + +The objection that broad statements of this kind, after all, rest largely +on negative evidence is obvious, but it has less force than may at first +be supposed; for, as might be expected from the circumstances of the +case, we possess more abundant positive evidence regarding Fishes and +marine Mollusks than respecting any other forms of animal life; and yet +these offer us, through the whole range of geological time, no species +ordinally distinct from those now living; while the far less numerous +class of Echinoderms presents three, and the Crustacea two, such orders, +though none of these come down later than the Palaeozoic age. Lastly, the +Reptilia present the extraordinary and exceptional phenomenon of as many +extinct as existing orders, if not more; the four mentioned maintaining +their existence from the Lias to the Chalk inclusive. + +Some years ago one of your Secretaries pointed out another kind of +positive palaeontological evidence tending towards the same conclusion-- +afforded by the existence of what he termed "persistent types" of +vegetable and of animal life.[4] He stated, on the authority of Dr. +Hooker, that there are Carboniferous plants which appear to be +generically identical with some now living; that the cone of the Oolitic +_Araucaria_ is hardly distinguishable from that of an existing species; +that a true _Pinus_ appears in the Purbecks and a _Juglans_ in the Chalk; +while, from the Bagshot Sands, a _Banksia_, the wood of which is not +distinguishable from that of species now living in Australia, had been +obtained. + +[Footnote 4: See the abstract of a Lecture "On the Persistent Types of +Animal Life," in the _Notices of the Meetings of the Royal Institution of +Great Britain_.--June 3, 1859, vol. iii. p. 151.] + +Turning to the animal kingdom, he affirmed the tabulate corals of the +Silurian rocks to be wonderfully like those which now exist; while even +the families of the Aporosa were all represented in the older Mesozoic +rocks. + +Among the Mollusca similar facts were adduced. Let it be borne in mind +that _Avicula, Mytilus, Chiton, Natica, Patella, Trochus, Discina, +Orbicula, Lingula, Rhynchonclla_, and _Nautilus_, all of which are +existing _genera_, are given without a doubt as Silurian in the last +edition of "Siluria"; while the highest forms of the highest Cephalopods +are represented in the Lias by a genus _Belemnoteuthis_, which presents +the closest relation to the existing _Loligo_. + +The two highest groups of the Annulosa, the Insecta and the Arachnida, +are represented in the Coal, either by existing genera, or by forms +differing from existing genera in quite minor peculiarities. + +Turning to the Vertebrata, the only palaeozoic Elasmobranch Fish of which +we have any complete knowledge is the Devonian and Carboniferous +_Pleuracanthus_, which differs no more from existing Sharks than these do +from one another. + +Again, vast as is the number of undoubtedly Ganoid fossil Fishes, and +great as is their range in time, a large mass of evidence has recently +been adduced to show that almost all those respecting which we possess +sufficient information, are referable to the same sub-ordinal groups as +the existing _Lepidosteus, Polypterus_, and Sturgeon; and that a singular +relation obtains between the older and the younger Fishes; the former, +the Devonian Ganoids, being almost all members of the same sub-order as +_Polypterus_, while the Mesozoic Ganoids are almost all similarly allied +to _Lepidosteus_.[5] + +[Footnote 5: "Memoirs of the Geological Survey of the United Kingdom.-- +Decade x. Preliminary Essay upon the Systematic Arrangement of the Fishes +of the Devonian Epoch."] + +Again, what can be more remarkable than the singular constancy of +structure preserved throughout a vast period of time by the family of the +Pycnodonts and by that of the true Coelacanths; the former persisting, +with but insignificant modifications, from the Carboniferous to the +Tertiary rocks, inclusive; the latter existing, with still less change, +from the Carboniferous rocks to the Chalk, inclusive? + +Among Reptiles, the highest living group, that of the Crocodilia, is +represented, at the early part of the Mesozoic epoch, by species +identical in the essential characters of their organisation with those +now living, and differing from the latter only in such matters as the +form of the articular facets of the vertebral centra, in the extent to +which the nasal passages are separated from the cavity of the mouth by +bone, and in the proportions of the limbs. + +And even as regards the Mammalia, the scanty remains of Triassic and +Oolitic species afford no foundation for the supposition that the +organisation of the oldest forms differed nearly so much from some of +those which now live as these differ from one another. + +It is needless to multiply these instances; enough has been said to +justify the statement that, in view of the immense diversity of known +animal and vegetable forms, and the enormous lapse of time indicated by +the accumulation of fossiliferous strata, the only circumstance to be +wondered at is, not that the changes of life, as exhibited by positive +evidence, have been so great but that they have been so small. + +Be they great or small, however, it is desirable to attempt to estimate +them. Let us, therefore, take each great division of the animal world in +succession, and, whenever an order or a family can be shown to have had a +prolonged existence, let us endeavour to ascertain how far the later +members of the group differ from the earlier ones. If these later +members, in all or in many cases, exhibit a certain amount of +modification, the fact is, so far, evidence in favour of a general law of +change; and, in a rough way, the rapidity of that change will be measured +by the demonstrable amount of modification. On the other hand, it must be +recollected that the absence of any modification, while it may leave the +doctrine of the existence of a law of change without positive support, +cannot possibly disprove all forms of that doctrine, though it may afford +a sufficient refutation of many of them. + +The PROTOZOA.--The Protozoa are represented throughout the whole range of +geological series, from the Lower Silurian formation to the present day. +The most ancient forms recently made known by Ehrenberg are exceedingly +like those which now exist: no one has ever pretended that the difference +between any ancient and any modern Foraminifera is of more than generic +value, nor are the oldest Foraminifera either simpler, more embryonic, or +less differentiated, than the existing forms. + +The COELENTERATA.--The Tabulate Corals have existed from the Silurian +epoch to the present day, but I am not aware that the ancient +_Heliolites_ possesses a single mark of a more embryonic or less +differentiated character, or less high organisation, than the existing +_Heliopora_. As for the Aporose Corals, in what respect is the Silurian +_Paloeocyclus_ less highly organised or more embryonic than the modern +_Fungia_, or the Liassic Aporosa than the existing members of the same +families? + +The _Mollusca_--In what sense is the living _Waldheimia_ less embryonic, +or more specialised, than the palaeozoic _Spirifer_; or the existing +_Rhynchonelloe, Cranioe, Discinoe, Linguloe_, than the Silurian species +of the same genera? In what sense can _Loligo_ or _Spirula_ be said to be +more specialised, or less embryonic, than _Belemnites_; or the modern +species of Lamellibranch and Gasteropod genera, than the Silurian species +of the same genera? + +The ANNULOSA.--The Carboniferous Insecta and Arachnida are neither less +specialised, nor more embryonic, than these that now live, nor are the +Liassic Cirripedia and Macrura; while several of the Brachyura, which +appear in the Chalk, belong to existing genera; and none exhibit either +an intermediate, or an embryonic, character. + +The VERTEBRATA.--Among fishes I have referred to the Coelacanthini +(comprising the genera _Coelacanthus, Holophagus, Undina_, and +_Macropoma_) as affording an example of a persistent type; and it is most +remarkable to note the smallness of the differences between any of these +fishes (affecting at most the proportions of the body and fins, and the +character and sculpture of the scales), notwithstanding their enormous +range in time. In all the essentials of its very peculiar structure, the +_Macropoma_ of the Chalk is identical with the _Coelacanthus_ of the +Coal. Look at the genus _Lepidotus_, again, persisting without a +modification of importance from the Liassic to the Eocene formations +inclusively. + +Or among the Teleostei--in what respect is the _Beryx_ of the Chalk more +embryonic, or less differentiated, than _Beryx lineatus_ of King George's +Sound? + +Or to turn to the higher Vertebrata--in what sense are the Liassic +Chelonia inferior to those which now exist? How are the Cretaceous +Ichthyosauria, Plesiosauria, or Pterosauria less embryonic, or more +differentiated, species than those of the Lias? + +Or lastly, in what circumstance is the _Phascolotherium_ more embryonic, +or of a more generalised type, than the modern Opossum; or a _Lophiodon_, +or a _Paloeotherium_, than a modern _Tapirus_ or _Hyrax_? + +These examples might be almost indefinitely multiplied, but surely they +are sufficient to prove that the only safe and unquestionable testimony +we can procure--positive evidence--fails to demonstrate any sort of +progressive modification towards a less embryonic, or less generalised, +type in a great many groups of animals of long-continued geological +existence. In these groups there is abundant evidence of variation--none +of what is ordinarily understood as progression; and, if the known +geological record is to be regarded as even any considerable fragment of +the whole, it is inconceivable that any theory of a necessarily +progressive development can stand, for the numerous orders and families +cited afford no trace of such a process. + +But it is a most remarkable fact, that, while the groups which have been +mentioned, and many besides, exhibit no sign of progressive modification, +there are others, co-existing with them, under the same conditions, in +which more or less distinct indications of such a process seems to be +traceable. Among such indications I may remind you of the predominance of +Holostome Gasteropoda in the older rocks as compared with that of +Siphonostone Gasteropoda in the later. A case less open to the objection +of negative evidence, however, is that afforded by the Tetrabranchiate +Cephalopoda, the forms of the shells and of the septal sutures exhibiting +a certain increase of complexity in the newer genera. Here, however, one +is met at once with the occurrence of _Orthoceras_ and _Baculites_ at the +two ends of the series, and of the fact that one of the simplest genera, +_Nautilus_, is that which now exists. + +The Crinoidea, in the abundance of stalked forms in the ancient +formations as compared with their present rarity, seem to present us with +a fair case of modification from a more embryonic towards a less +embryonic condition. But then, on careful consideration of the facts, the +objection arises that the stalk, calyx, and arms of the palaeozoic Crinoid +are exceedingly different from the corresponding organs of a larval +_Comatula_; and it might with perfect justice be argued that +_Actinocrinus_ and _Eucalyptocrinus_, for example, depart to the full as +widely, in one direction, from the stalked embryo of _Comatula_, as +_Comatula_ itself does in the other. + +The Echinidea, again, are frequently quoted as exhibiting a gradual +passage from a more generalised to a more specialised type, seeing that +the elongated, or oval, Spatangoids appear after the spheroidal +Echinoids. But here it might be argued, on the other hand, that the +spheroidal Echinoids, in reality, depart further from the general plan +and from the embryonic form than the elongated Spatangoids do; and that +the peculiar dental apparatus and the pedicellariae of the former are +marks of at least as great differentiation as the petaloid ambulacra and +semitae of the latter. + +Once more, the prevalence of Macrurous before Brachyurous Podophthalmia +is, apparently, a fair piece of evidence in favour of progressive +modification in the same order of Crustacea; and yet the case will not +stand much sifting, seeing that the Macrurous Podophthalmia depart as far +in one direction from the common type of Podophthalmia, or from any +embryonic condition of the Brachyura, as the Brachyura do in the other; +and that the middle terms between Macrura and Brachyura--the Anomura--are +little better represented in the older Mesozoic rocks than the Brachyura +are. + +None of the cases of progressive modification which are cited from among +the Invertebrata appear to me to have a foundation less open to criticism +than these; and if this be so, no careful reasoner would, I think, be +inclined to lay very great stress upon them. Among the Vertebrata, +however, there are a few examples which appear to be far less open to +objection. + +It is, in fact, true of several groups of Vertebrata which have lived +through a considerable range of time, that the endoskeleton (more +particularly the spinal column) of the older genera presents a less +ossified, and, so far, less differentiated, condition than that of the +younger genera. Thus the Devonian Ganoids, though almost all members of +the same sub-order as _Polypterus_, and presenting numerous important +resemblances to the existing genus, which possesses biconclave vertebrae, +are, for the most part, wholly devoid of ossified vertebral centra. The +Mesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, while +the existing _Lepidosteus_ has Salamandroid, opisthocoelous, vertebrae. +So, none of the Palaeozoic Sharks have shown themselves to be possessed of +ossified vertebrae, while the majority of modern Sharks possess such +vertebrae. Again, the more ancient Crocodilia and Lacertilia have vertebrae +with the articular facets of their centra flattened or biconcave, while +the modern members of the same group have them procoelous. But the most +remarkable examples of progressive modification of the vertebral column, +in correspondence with geological age, are those afforded by the +Pycnodonts among fish, and the Labyrinthodonts among Amphibia. + +The late able ichthyologist Heckel pointed out the fact, that, while the +Pycnodonts never possess true vertebral centra, they differ in the degree +of expansion and extension of the ends of the bony arches of the vertebrae +upon the sheath of the notochord; the Carboniferous forms exhibiting +hardly any such expansion, while the Mesozoic genera present a greater +and greater development, until, in the Tertiary forms, the expanded ends +become suturally united so as to form a sort of false vertebra. Hermann +von Meyer, again, to whose luminous researches we are indebted for our +present large knowledge of the organisation of the older Labyrinthodonts, +has proved that the Carboniferous _Archegosaurus_ had very imperfectly +developed vertebral centra, while the Triassic _Mastodonsaurus_ had the +same parts completely ossified.[6] + +[Footnote 6: As this Address is passing through the press (March 7, +1862), evidence lies before me of the existence of a new Labyrinthodont +(_Pholidogaster_), from the Edinburgh coal-field with well-ossified +vertebral centra.] + +The regularity and evenness of the dentition of the _Anoplotherium_, as +contrasted with that of existing Artiodactyles, and the assumed nearer +approach of the dentition of certain ancient Carnivores to the typical +arrangement, have also been cited as exemplifications of a law of +progressive development, but I know of no other cases based on positive +evidence which are worthy of particular notice. + +What then does an impartial survey of the positively ascertained truths +of palaeontology testify in relation to the common doctrines of +progressive modification, which suppose that modification to have taken +place by a necessary progress from more to less embryonic forms, or from +more to less generalised types, within the limits of the period +represented by the fossiliferous rocks? + +It negatives those doctrines; for it either shows us no evidence of any +such modification, or demonstrates it to have been very slight; and as to +the nature of that modification, it yields no evidence whatsoever that +the earlier members of any long-continued group were more generalised in +structure than the later ones. To a certain extent, indeed, it may be +said that imperfect ossification of the vertebral column is an embryonic +character; but, on the other hand, it would be extremely incorrect to +suppose that the vertebral columns of the older Vertebrata are in any +sense embryonic in their whole structure. + +Obviously, if the earliest fossiliferous rocks now known are coeval with +the commencement of life, and if their contents give us any just +conception of the nature and the extent of the earliest fauna and flora, +the insignificant amount of modification which can be demonstrated to +have taken place in any one group of animals, or plants, is quite +incompatible with the hypothesis that all living forms are the results of +a necessary process of progressive development, entirely comprised within +the time represented by the fossiliferous rocks. + +Contrariwise, any admissible hypothesis of progressive modification must +be compatible with persistence without progression, through indefinite +periods. And should such an hypothesis eventually be proved to be true, +in the only way in which it can be demonstrated, viz. by observation and +experiment upon the existing forms of life, the conclusion will +inevitably present itself, that the Palaeozoic Mesozoic, and Cainozoic +faunae and florae, taken together, bear somewhat the same proportion to the +whole series of living beings which have occupied this globe, as the +existing fauna and flora do to them. + +Such are the results of palaeontology as they appear, and have for some +years appeared, to the mind of an inquirer who regards that study simply +as one of the applications of the great biological sciences, and who +desires to see it placed upon the same sound basis as other branches of +physical inquiry. If the arguments which have been brought forward are +valid, probably no one, in view of the present state of opinion, will be +inclined to think the time wasted which has been spent upon their +elaboration. + + + +X + + +GEOLOGICAL REFORM + +[1869] + +"A great reform in geological speculation seems now to have become +necessary." + +"It is quite certain that a great mistake has been made--that British +popular geology at the present time is in direct opposition to the +principles of Natural Philosophy."[1] + +[Footnote 1: On Geological Time. By Sir W. Thomson, LL.D. _Transactions +of the Geological Society of Glasgow_, vol. iii.] + +In reviewing the course of geological thought during the past year, for +the purpose of discovering those matters to which I might most fitly +direct your attention in the Address which it now becomes my duty to +deliver from the Presidential Chair, the two somewhat alarming sentences +which I have just read, and which occur in an able and interesting essay +by an eminent natural philosopher, rose into such prominence before my +mind that they eclipsed everything else. + +It surely is a matter of paramount importance for the British geologists +(some of them very popular geologists too) here in solemn annual session +assembled, to inquire whether the severe judgment thus passed upon them +by so high an authority as Sir William Thomson is one to which they must +plead guilty _sans phrase_, or whether they are prepared to say "not +guilty," and appeal for a reversal of the sentence to that higher court +of educated scientific opinion to which we are all amenable. + +As your attorney-general for the time being, I thought I could not do +better than get up the case with a view of advising you. It is true that +the charges brought forward by the other side involve the consideration +of matters quite foreign to the pursuits with which I am ordinarily +occupied; but, in that respect, I am only in the position which is, nine +times out of ten, occupied by counsel, who nevertheless contrive to gain +their causes, mainly by force of mother-wit and common-sense, aided by +some training in other intellectual exercises. + +Nerved by such precedents, I proceed to put my pleading before you. + +And the first question with which I propose to deal is, What is it to +which Sir W. Thomson refers when he speaks of "geological speculation" +and "British popular geology"? + +I find three, more or less contradictory, systems of geological thought, +each of which might fairly enough claim these appellations, standing side +by side in Britain. I shall call one of them CATASTROPHISM, another +UNIFORMITARIANISM, the third EVOLUTIONISM; and I shall try briefly to +sketch the characters of each, that you may say whether the +classification is, or is not, exhaustive. + +By CATASTROPHISM, I mean any form of geological speculation which, in +order to account for the phenomena of geology, supposes the operation of +forces different in their nature, or immeasurably different in power, +from those which we at present see in action in the universe. + +The Mosaic cosmogony is, in this sense, catastrophic, because it assumes +the operation of extra-natural power. The doctrine of violent upheavals, +_debacles_, and cataclysms in general, is catastrophic, so far as it +assumes that these were brought about by causes which have now no +parallel. There was a time when catastrophism might, pre-eminently, have +claimed the title of "British popular geology"; and assuredly it has yet +many adherents, and reckons among its supporters some of the most +honoured members of this Society. + +By UNIFORMITARIANISM, I mean especially, the teaching of Hutton and of +Lyell. + +That great though incomplete work, "The Theory of the Earth," seems to me +to be one of the most remarkable contributions to geology which is +recorded in the annals of the science. So far as the not-living world is +concerned, uniformitarianism lies there, not only in germ, but in blossom +and fruit. + +If one asks how it is that Hutton was led to entertain views so far in +advance of those prevalent in his time, in some respects; while, in +others, they seem almost curiously limited, the answer appears to me to +be plain. + +Hutton was in advance of the geological speculation of his time, because, +in the first place, he had amassed a vast store of knowledge of the facts +of geology, gathered by personal observation in travels of considerable +extent; and because, in the second place, he was thoroughly trained in +the physical and chemical science of his day, and thus possessed, as much +as any one in his time could possess it, the knowledge which is requisite +for the just interpretation of geological phenomena, and the habit of +thought which fits a man for scientific inquiry. + +It is to this thorough scientific training that I ascribe Hutton's steady +and persistent refusal to look to other causes than those now in +operation, for the explanation of geological phenomena. + +Thus he writes:--"I do not pretend, as he [M. de Luc] does in his theory, +to describe the beginning of things. I take things such as I find them at +present; and from these I reason with regard to that which must have +been."[2] + +[Footnote 2: _The Theory of the Earth_, vol. i. p. 173, note.] + +And again:--"A theory of the earth, which has for object truth, can have +no retrospect to that which had preceded the present order of the world; +for this order alone is what we have to reason upon; and to reason +without data is nothing but delusion. A theory, therefore, which is +limited to the actual constitution of this earth cannot be allowed to +proceed one step beyond the present order of things."[3] + +[Footnote 3: _Ibid._, vol. i. p. 281.] + +And so clear is he, that no causes beside such as are now in operation +are needed to account for the character and disposition of the components +of the crust of the earth, that he says, broadly and boldly:--" ... There +is no part of the earth which has not had the same origin, so far as this +consists in that earth being collected at the bottom of the sea, and +afterwards produced, as land, along with masses of melted substances, by +the operation of mineral causes."[4] + +[Footnote 4: _Ibid._. p. 371.] + +But other influences were at work upon Hutton beside those of a mind +logical by nature, and scientific by sound training; and the peculiar +turn which his speculations took seems to me to be unintelligible, unless +these be taken into account. The arguments of the French astronomers and +mathematicians, which, at the end of the last century, were held to +demonstrate the existence of a compensating arrangement among the +celestial bodies, whereby all perturbations eventually reduced themselves +to oscillations on each side of a mean position, and the stability of the +solar system was secured, had evidently taken strong hold of Hutton's +mind. + +In those oddly constructed periods which seem to have prejudiced many +persons against reading his works, but which are full of that peculiar, +if unattractive, eloquence which flows from mastery of the subject, +Hutton says:-- + +"We have now got to the end of our reasoning; we have no data further to +conclude immediately from that which actually is. But we have got enough; +we have the satisfaction to find, that in Nature there is wisdom, system, +and consistency. For having, in the natural history of this earth, seen a +succession of worlds, we may from this conclude that there is a system in +Nature; in like manner as, from seeing revolutions of the planets, it is +concluded, that there is a system by which they are intended to continue +those revolutions. But if the succession of worlds is established in the +system of nature, it is in vain to look for anything higher in the origin +of the earth. The result, therefore, of this physical inquiry is, that we +find no vestige of a beginning,--no prospect of an end."[5] + +[Footnote 5: _Ibid._, vol. i. p. 200.] + +Yet another influence worked strongly upon Hutton. Like most philosophers +of his age, he coquetted with those final causes which have been named +barren virgins, but which might be more fitly termed the _hetairoe_ of +philosophy, so constantly have they led men astray. The final cause of +the existence of the world is, for Hutton, the production of life and +intelligence. + +"We have now considered the globe of this earth as a machine, constructed +upon chemical as well as mechanical principles, by which its different +parts are all adapted, in form, in quality, and in quantity, to a certain +end; an end attained with certainty or success; and an end from which we +may perceive wisdom, in contemplating the means employed. + +"But is this world to be considered thus merely as a machine, to last no +longer than its parts retain their present position, their proper forms +and qualities? Or may it not be also considered as an organised body? +such as has a constitution in which the necessary decay of the machine is +naturally repaired, in the exertion of those productive powers by which +it had been formed. + +"This is the view in which we are now to examine the globe; to see if +there be, in the constitution of this world, a reproductive operation, by +which a ruined constitution may be again repaired, and a duration or +stability thus procured to the machine, considered as a world sustaining +plants and animals."[6] + +[Footnote 6: _Ibid._, vol. i. pp. 16, 17.] + +Kirwan, and the other Philistines of the day, accused Hutton of declaring +that his theory implied that the world never had a beginning, and never +differed in condition from its present state. Nothing could be more +grossly unjust, as he expressly guards himself against any such +conclusion in the following terms:-- + +"But in thus tracing back the natural operations which have succeeded +each other, and mark to us the course of time past, we come to a period +in which we cannot see any farther. This, however, is not the beginning +of the operations which proceed in time and according to the wise economy +of this world; nor is it the establishing of that which, in the course of +time, had no beginning; it is only the limit of our retrospective view of +those operations which have come to pass in time, and have been conducted +by supreme intelligence."[7] + +[Footnote 7: _Ibid._, vol. i. p. 223.] + +I have spoken of Uniformitarianism as the doctrine of Hutton and of +Lyell. If I have quoted the older writer rather than the newer, it is +because his works are little known, and his claims on our veneration too +frequently forgotten, not because I desire to dim the fame of his eminent +successor. Few of the present generation of geologists have read +Playfair's "Illustrations," fewer still the original "Theory of the +Earth"; the more is the pity; but which of us has not thumbed every page +of the "Principles of Geology"? I think that he who writes fairly the +history of his own progress in geological thought, will not be able to +separate his debt to Hutton from his obligations to Lyell; and the +history of the progress of individual geologists is the history of +geology. + + +No one can doubt that the influence of uniformitarian views has been +enormous, and, in the main, most beneficial and favourable to the +progress of sound geology. + +Nor can it be questioned that Uniformitarianism has even a stronger title +than Catastrophism to call itself the geological speculation of Britain, +or, if you will, British popular geology. For it is eminently a British +doctrine, and has even now made comparatively little progress on the +continent of Europe. Nevertheless, it seems to me to be open to serious +criticism upon one of its aspects. + +I have shown how unjust was the insinuation that Hutton denied a +beginning to the world. But it would not be unjust to say that he +persistently in practice, shut his eyes to the existence of that prior +and different state of things which, in theory, he admitted; and, in this +aversion to look beyond the veil of stratified rocks, Lyell follows him. + +Hutton and Lyell alike agree in their indisposition to carry their +speculations a step beyond the period recorded in the most ancient strata +now open to observation in the crust of the earth. This is, for Hutton, +"the point in which we cannot see any farther"; while Lyell tells us,-- + +"The astronomer may find good reasons for ascribing the earth's form to +the original fluidity of the mass, in times long antecedent to the first +introduction of living beings into the planet; but the geologist must be +content to regard the earliest monuments which it is his task to +interpret, as belonging to a period when the crust had already acquired +great solidity and thickness, probably as great as it now possesses, and +when volcanic rocks, not essentially differing from those now produced, +were formed from time to time, the intensity of volcanic heat being +neither greater nor less than it is now."[8] + +[Footnote 8: _Principles of Geology_, vol. ii. p. 211.] + +And again, "As geologists, we learn that it is not only the present +condition of the globe which has been suited to the accommodation of +myriads of living creatures, but that many former states also have been +adapted to the organisation and habits of prior races of beings. The +disposition of the seas, continents and islands, and the climates, have +varied; the species likewise have been changed; and yet they have all +been so modelled, on types analogous to those of existing plants and +animals, as to indicate, throughout, a perfect harmony of design and +unity of purpose. To assume that the evidence of the beginning, or end, +of so vast a scheme lies within the reach of our philosophical inquiries, +or even of our speculations, appears to be inconsistent with a just +estimate of the relations which subsist between the finite powers of man +and the attributes of an infinite and eternal Being."[9] + +[Footnote 9: _Ibid._, vol. ii. p. 613.] + +The limitations implied in these passages appear to me to constitute the +weakness and the logical defect of Uniformitarianism. No one will impute +blame to Hutton that, in face of the imperfect condition, in his day, of +those physical sciences which furnish the keys to the riddles of geology, +he should have thought it practical wisdom to limit his theory to an +attempt to account for "the present order of things"; but I am at a loss +to comprehend why, for all time, the geologist must be content to regard +the oldest fossiliferous rocks as the _ultima Thule_ of his science; or +what there is inconsistent with the relations between the finite and the +infinite mind, in the assumption, that we may discern somewhat of the +beginning, or of the end, of this speck in space we call our earth. The +finite mind is certainly competent to trace out the development of the +fowl within the egg; and I know not on what ground it should find more +difficulty in unravelling the complexities Of the development of the +earth. In fact, as Kant has well remarked,[10] the cosmical process is +really simpler than the biological. + +[Footnote 10: "Man darf es sich also nicht befremden lassen, wenn ich +mich unterstehe zu sagen, dass eher die Bildung aller Himmelskoerper, die +Ursache ihrer Bewegungen, kurz der Ursprung der gantzen gegenwaertigen +Verfassung des Weltbaues werden koennen eingesehen werden, ehe die +Erzeugung eines einzigen Krautes oder einer Raupe aus mechanischen +Gruenden, deutlich und vollstaendig kund werden wird."--KANT'S _Saemmtliche +Werke_, Bd. i. p. 220.] + +This attempt to limit, at a particular point, the progress of inductive +and deductive reasoning from the things which are, to those which were-- +this faithlessness to its own logic, seems to me to have cost +Uniformitarianism the place, as the permanent form of geological +speculation, which it might otherwise have held. + +It remains that I should put before you what I understand to be the third +phase of geological speculation--namely, EVOLUTIONISM. + +I shall not make what I have to say on this head clear, unless I diverge, +or seem to diverge, for a while, from the direct path of my discourse, so +far as to explain what I take to be the scope of geology itself. I +conceive geology to be the history of the earth, in precisely the same +sense as biology is the history of living beings; and I trust you will +not think that I am overpowered by the influence of a dominant pursuit if +I say that I trace a close analogy between these two histories. + +If I study a living being, under what heads does the knowledge I obtain +fall? I can learn its structure, or what we call its ANATOMY; and its +DEVELOPMENT, or the series of changes which it passes through to acquire +its complete structure. Then I find that the living being has certain +powers resulting from its own activities, and the interaction of these +with the activities of other things--the knowledge of which is +PHYSIOLOGY. Beyond this the living being has a position in space and +time, which is its DISTRIBUTION. All these form the body of ascertainable +facts which constitute the _status quo_ of the living creature. But these +facts have their causes; and the ascertainment of these causes is the +doctrine of AETIOLOGY. + +If we consider what is knowable about the earth, we shall find that such +earth-knowledge--if I may so translate the word geology--falls into the +same categories. + +What is termed stratigraphical geology is neither more nor less than the +anatomy of the earth; and the history of the succession of the formations +is the history of a succession of such anatomies, or corresponds with +development, as distinct from generation. + +The internal heat of the earth, the elevation and depression of its +crust, its belchings forth of vapours, ashes, and lava, are its +activities, in as strict a sense as are warmth and the movements and +products of respiration the activities of an animal. The phenomena of the +seasons, of the trade winds, of the Gulf-stream, are as much the results +of the reaction between these inner activities and outward forces, as are +the budding of the leaves in spring and their falling in autumn the +effects of the interaction between the organisation of a plant and the +solar light and heat. And, as the study of the activities of the living +being is called its physiology, so are these phenomena the subject-matter +of an analogous telluric physiology, to which we sometimes give the name +of meteorology, sometimes that of physical geography, sometimes that of +geology. Again, the earth has a place in space and in time, and relations +to other bodies in both these respects, which constitute its +distribution. This subject is usually left to the astronomer; but a +knowledge of its broad outlines seems to me to be an essential +constituent of the stock of geological ideas. + +All that can be ascertained concerning the structure, succession of +conditions, actions, and position in space of the earth, is the matter of +fact of its natural history. But, as in biology, there remains the matter +of reasoning from these facts to their causes, which is just as much +science as the other, and indeed more; and this constitutes geological +aetiology. + +Having regard to this general scheme of geological knowledge and thought, +it is obvious that geological speculation may be, so to speak, anatomical +and developmental speculation, so far as it relates to points of +stratigraphical arrangement which are out of reach of direct observation; +or, it may be physiological speculation so far as it relates to +undetermined problems relative to the activities of the earth; or, it may +be distributional speculation, if it deals with modifications of the +earth's place in space; or, finally, it will be aetiological speculation +if it attempts to deduce the history of the world, as a whole, from the +known properties of the matter of the earth, in the conditions in which +the earth has been placed. + +For the purposes of the present discourse I may take this last to be what +is meant by "geological speculation." + +Now Uniformitarianism, as we have seen, tends to ignore geological +speculation in this sense altogether. + +The one point the catastrophists and the uniformitarians agreed upon, +when this Society was founded, was to ignore it. And you will find, if +you look back into our records, that our revered fathers in geology +plumed themselves a good deal upon the practical sense and wisdom of this +proceeding. As a temporary measure, I do not presume to challenge its +wisdom; but in all organised bodies temporary changes are apt to produce +permanent effects; and as time has slipped by, altering all the +conditions which may have made such mortification of the scientific flesh +desirable, I think the effect of the stream of cold water which has +steadily flowed over geological speculation within these walls has been +of doubtful beneficence. + +The sort of geological speculation to which I am now referring +(geological aetiology, in short) was created, as a science, by that famous +philosopher Immanuel Kant, when, in 1775, he wrote his "General Natural +History and Theory of the Celestial Bodies; or an Attempt to account for +the Constitutional and the Mechanical Origin of the Universe upon +Newtonian principles."[11] + +[Footnote 11: Grant (_History of Physical Astronomy_, p. 574) makes but +the briefest reference to Kant.] + +In this very remarkable but seemingly little-known treatise,[12] Kant +expounds a complete cosmogony, in the shape of a theory of the causes +which have led to the development of the universe from diffused atoms of +matter endowed with simple attractive and repulsive forces. + +[Footnote 12: "Allgemeine Naturgeschichte und Theorie des Himmels; oder +Versuch von der Verfassung und dem mechanischen Ursprunge des ganzen +Weltgebaeudes nach Newton'schen Grundsatzen abgehandelt."--KANT'S +_Saemmtliche Werke_, Bd. i. p. 207.] + +"Give me matter," says Kant, "and I will build the world;" and he +proceeds to deduce from the simple data from which he starts, a doctrine +in all essential respects similar to the well-known "Nebular Hypothesis" +of Laplace.[13] He accounts for the relation of the masses and the +densities of the planets to their distances from the sun, for the +eccentricities of their orbits, for their rotations, for their +satellites, for the general agreement in the direction of rotation among +the celestial bodies, for Saturn's ring, and for the zodiacal light. He +finds in each system of worlds, indications that the attractive force of +the central mass will eventually destroy its organisation, by +concentrating upon itself the matter of the whole system; but, as the +result of this concentration, he argues for the development of an amount +of heat which will dissipate the mass once more into a molecular chaos +such as that in which it began. + +[Footnote 13: _Systeme du Monde_, tome ii. chap. 6.] + +Kant pictures to himself the universe as once an infinite expansion of +formless and diffused matter. At one point of this he supposes a single +centre of attraction set up; and, by strict deductions from admitted +dynamical principles, shows how this must result in the development of a +prodigious central body, surrounded by systems of solar and planetary +worlds in all stages of development. In vivid language he depicts the +great world-maelstrom, widening the margins of its prodigious eddy in the +slow progress of millions of ages, gradually reclaiming more and more of +the molecular waste, and converting chaos into cosmos. But what is gained +at the margin is lost in the centre; the attractions of the central +systems bring their constituents together, which then, by the heat +evolved, are converted once more into molecular chaos. Thus the worlds +that are, lie between the ruins of the worlds that have been, and the +chaotic materials of the worlds that shall be; and in spite of all waste +and destruction, Cosmos is extending his borders at the expense of Chaos. + +Kant's further application of his views to the earth itself is to be +found in his "Treatise on Physical Geography"[14] (a term under which the +then unknown science of geology was included), a subject which he had +studied with very great care and on which he lectured for many years. The +fourth section of the first part of this Treatise is called "History of +the great Changes which the Earth has formerly undergone and is still +undergoing," and is, in fact, a brief and pregnant essay upon the +principles of geology. Kant gives an account first "of the gradual +changes which are now taking place" under the heads of such as are caused +by earthquakes, such as are brought about by rain and rivers, such as are +effected by the sea, such as are produced by winds and frost; and, +finally, such as result from the operations of man. + +[Footnote 14: Kant's _Saemmtliche Werke_, Bd. viii. p. 145.] + +The second part is devoted to the "Memorials of the Changes which the +Earth has undergone in remote Antiquity." These are enumerated as:--A. +Proofs that the sea formerly covered the whole earth. B. Proofs that the +sea has often been changed into dry land and then again into sea. C. A +discussion of the various theories of the earth put forward by +Scheuchzer, Moro, Bonnet, Woodward, White, Leibnitz, Linnaeus, and Buffon. + +The third part contains an "Attempt to give a sound explanation of the +ancient history of the earth." + +I suppose that it would be very easy to pick holes in the details of +Kant's speculations, whether cosmological, or specially telluric, in +their application. But for all that, he seems to me to have been the +first person to frame a complete system of geological speculation by +founding the doctrine of evolution. + +With as much truth as Hutton, Kant could say, "I take things just as I +find them at present, and, from these, I reason with regard to that which +must have been." Like Hutton, he is never tired of pointing out that "in +Nature there is wisdom, system, and consistency." And, as in these great +principles, so in believing that the cosmos has a reproductive operation +"by which a ruined constitution may be repaired," he forestalls Hutton; +while, on the other hand, Kant is true to science. He knows no bounds to +geological speculation but those of the intellect. He reasons back to a +beginning of the present state of things; he admits the possibility of an +end. + +I have said that the three schools of geological speculation which I have +termed Catastrophism, Uniformitarianism, and Evolutionism, are commonly +supposed to be antagonistic to one another; and I presume it will have +become obvious that in my belief, the last is destined to swallow up the +other two. But it is proper to remark that each of the latter has kept +alive the tradition of precious truths. + +CATASTROPHISM has insisted upon the existence of a practically unlimited +bank of force, on which the theorist might draw; and it has cherished the +idea of the development of the earth from a state in which its form, and +the forces which it exerted, were very different from those we now know. +That such difference of form and power once existed is a necessary part +of the doctrine of evolution. + +UNIFORMITARIANISM, on the other hand, has with equal justice insisted +upon a practically unlimited bank of time, ready to discount any quantity +of hypothetical paper. It has kept before our eyes the power of the +infinitely little, time being granted, and has compelled us to exhaust +known causes, before flying to the unknown. + +To my mind there appears to be no sort of necessary theoretical +antagonism between Catastrophism and Uniformitarianism. On the contrary, +it is very conceivable that catastrophes may be part and parcel of +uniformity. Let me illustrate my case by analogy. The working of a clock +is a model of uniform action; good time-keeping means uniformity of +action. But the striking of the clock is essentially a catastrophe; the +hammer might be made to blow up a barrel of gunpowder, or turn on a +deluge of water; and, by proper arrangement, the clock, instead of +marking the hours, might strike at all sorts of irregular periods, never +twice alike, in the intervals, force, or number of its blows. +Nevertheless, all these irregular, and apparently lawless, catastrophes +would be the result of an absolutely uniformitarian action; and we might +have two schools of clock-theorists, one studying the hammer and the +other the pendulum. + +Still less is there any necessary antagonists between either of these +doctrines and that of Evolution, which embraces all that is sound in both +Catastrophism and Uniformitarianism, while it rejects the arbitrary +assumptions of the one and the, as arbitrary, limitations of the other. +Nor is the value of the doctrine of Evolution to the philosophic thinker +diminished by the fact that it applies the same method to the living and +the not-living world; and embraces, in one stupendous analogy, the growth +of a solar system from molecular chaos, the shaping of the earth from the +nebulous cub-hood of its youth, through innumerable changes and +immeasurable ages, to its present form; and the development of a living +being from the shapeless mass of protoplasm we term a germ. + +I do not know whether Evolutionism can claim that amount of currency +which would entitle it to be called British popular geology; but, more or +less vaguely, it is assuredly present in the minds of most geologists. + +Such being the three phases of geological speculation, we are now in +position to inquire which of these it is that Sir William Thomson calls +upon us to reform in the passages which I have cited. + +It is obviously Uniformitarianism which the distinguished physicist takes +to be the representative of geological speculation in general. And thus a +first issue is raised, inasmuch as many persons (and those not the least +thoughtful among the younger geologists) do not accept strict +Uniformitarianism as the final form of geological speculation. We should +say, if Hutton and Playfair declare the course of the world to have been +always the same, point out the fallacy by all means; but, in so doing, do +not imagine that you are proving modern geology to be in opposition to +natural philosophy. I do not suppose that, at the present day, any +geologist would be found to maintain absolute Uniformitarianism, to deny +that the rapidity of the rotation of the earth _may_ be diminishing, that +the sun _may_ be waxing dim, or that the earth itself _may_ be cooling. +Most of us, I suspect, are Gallios, "who care for none of these things," +being of opinion that, true or fictitious, they have made no practical +difference to the earth, during the period of which a record is preserved +in stratified deposits. + +The accusation that we have been running counter to the _principles_ of +natural philosophy, therefore, is devoid of foundation. The only question +which can arise is whether we have, or have not, been tacitly making +assumptions which are in opposition to certain conclusions which may be +drawn from those principles. And this question subdivides itself into +two:--the first, are we really contravening such conclusions? the second, +if we are, are those conclusions so firmly based that we may not +contravene them? I reply in the negative to both these questions, and I +will give you my reasons for so doing. Sir William Thomson believes that +he is able to prove, by physical reasonings, "that the existing state of +things on the earth, life on the earth--all geological history showing +continuity of life--must be limited within some such period of time as +one hundred million years" (_loc. cit._ p. 25). + +The first inquiry which arises plainly is, has it ever been denied that +this period _may_ be enough for the purposes of geology? + +The discussion of this question is greatly embarrassed by the vagueness +with which the assumed limit is, I will not say defined, but indicated,-- +"some such period of past time as one hundred million years." Now does +this mean that it may have been two, or three, or four hundred million +years? Because this really makes all the difference.[15] + +[Footnote 15: Sir William Thomson implies (_loc. cit_. p. 16) that the +precise time is of no consequence: "the principle is the same"; but, as +the principle is admitted, the whole discussion turns on its practical +results.] + +I presume that 100,000 feet may be taken as a full allowance for the +total thickness of stratified rocks containing traces of life; 100,000 +divided by 100,000,000 = 0.001. Consequently, the deposit of 100,000 feet +of stratified rock in 100,000,000 years means that the deposit has taken +place at the rate of 1/1000 of a foot, or, say, 1/83 of an inch, per +annum. + +Well, I do not know that any one is prepared to maintain that, even +making all needful allowances, the stratified rocks may not have been +formed, on the average, at the rate of 1/83 of an inch per annum. I +suppose that if such could be shown to be the limit of world-growth, we +could put up with the allowance without feeling that our speculations had +undergone any revolution. And perhaps, after all, the qualifying phrase +"some such period" may not necessitate the assumption of more than 1/166 +or 1/249 or 1/332 of an inch of deposit per year, which, of course, would +give us still more ease and comfort. + +But, it may be said, that it is biology, and not geology, which asks for +so much time--that the succession of life demands vast intervals; but +this appears to me to be reasoning in a circle. Biology takes her time +from geology. The only reason we have for believing in the slow rate of +the change in living forms is the fact that they persist through a series +of deposits which, geology informs us, have taken a long while to make. +If the geological clock is wrong, all the naturalist will have to do is +to modify his notions of the rapidity of change accordingly. And I +venture to point out that, when we are told that the limitation of the +period during which living beings have inhabited this planet to one, two, +or three hundred million years requires a complete revolution in +geological speculation, the _onus probandi_ rests on the maker of the +assertion, who brings forward not a shadow of evidence in its support. + +Thus, if we accept the limitation of time placed before us by Sir W. +Thomson, it is not obvious, on the face of the matter, that we shall have +to alter, or reform, our ways in any appreciable degree; and we may +therefore proceed with much calmness, and indeed much indifference, as to +the result, to inquire whether that limitation is justified by the +arguments employed in its support. + +These arguments are three in number.-- + +I. The first is based upon the undoubted fact that the tides tend to +retard the rate of the earth's rotation upon its axis. That this must be +so is obvious, if one considers, roughly, that the tides result from the +pull which the sun and the moon exert upon the sea, causing it to act as +a sort of break upon the rotating solid earth. + +Kant, who was by no means a mere "abstract philosopher," but a good +mathematician and well versed in the physical science of his time, not +only proved this in an essay of exquisite clearness and intelligibility, +now more than a century old,[16] but deduced from it some of its more +important consequences, such as the constant turning of one face of the +moon towards the earth. + +[Footnote 16: "Untersuchung der Frage oh die Erde in ihrer Umdrehung um +die Achse, wodurch sie die Abwechselung des Tages und der Nacht +hervorbringt, einige Veraenderung seit den ersten Zeiten ihres Ursprunges +erlitten habe, &c."--KANT's _Saemmntliche Werke_, Bd. i. p. 178.] + +But there is a long step from the demonstration of a tendency to the +estimation of the practical value of that tendency, which is all with +which we are at present concerned. The facts bearing on this point appear +to stand as follows:-- + +It is a matter of observation that the moon's mean motion is (and has for +the last 3,000 years been) undergoing an acceleration, relatively to the +rotation of the earth. Of course this may result from one of two causes: +the moon may really have been moving more swiftly in its orbit; or the +earth may have been rotating more slowly on its axis. + +Laplace believed he had accounted for this phenomenon by the fact that +the eccentricity of the earth's orbit has been diminishing throughout +these 3,000 years. This would produce a diminution of the mean attraction +of the sun on the moon; or, in other words, an increase in the attraction +of the earth on the moon; and, consequently, an increase in the rapidity +of the orbital motion of the latter body. Laplace, therefore, laid the +responsibility of the acceleration upon the moon, and if his views were +correct, the tidal retardation must either be insignificant in amount, or +be counteracted by some other agency. + +Our great astronomer, Adams, however, appears to have found a flaw in +Laplace's calculation, and to have shown that only half the observed +retardation could be accounted for in the way he had suggested. There +remains, therefore, the other half to be accounted for; and here, in the +absence of all positive knowledge, three sets of hypotheses have been +suggested. + +(_a_.) M. Delaunay suggests that the earth is at fault, in consequence of +the tidal retardation. Messrs. Adams, Thomson, and Tait work out this +suggestion, and, "on a certain assumption as to the proportion of +retardations due to the sun and moon," find the earth may lose twenty-two +seconds of time in a century from this cause.[17] + +[Footnote 17: Sir W. Thomson, _loc. cit_. p. 14.] + +(_b_.) But M. Dufour suggests that the retardation of the earth (which is +hypothetically assumed to exist) may be due in part, or wholly, to the +increase of the moment of inertia of the earth by meteors falling upon +its surface. This suggestion also meets with the entire approval of Sir +W. Thomson, who shows that meteor-dust, accumulating at the rate of one +foot in 4,000 years, would account for the remainder of retardation.[18] + +[Footnote 18: _Ibid._ p. 27.] + +(_c_.) Thirdly, Sir W. Thomson brings forward an hypothesis of his own +with respect to the cause of the hypothetical retardation of the earth's +rotation:-- + +"Let us suppose ice to melt from the polar regions (20 deg. round each pole, +we may say) to the extent of something more than a foot thick, enough to +give 1.1 foot of water over those areas, or 0.006 of a foot of water if +spread over the whole globe, which would, in reality, raise the sea-level +by only some such undiscoverable difference as three-fourths of an inch +or an inch. This, or the reverse, which we believe might happen any year, +and could certainly not be detected without far more accurate +observations and calculations for the mean sea-level than any hitherto +made, would slacken or quicken the earth's rate as a timekeeper by one- +tenth of a second per year."[19] + +[Footnote 19: _Ibid._] + +I do not presume to throw the slightest doubt upon the accuracy of any of +the calculations made by such distinguished mathematicians as those who +have made the suggestions I have cited. On the contrary, it is necessary +to my argument to assume that they are all correct. But I desire to point +out that this seems to be one of the many cases in which the admitted +accuracy of mathematical process is allowed to throw a wholly +inadmissible appearance of authority over the results obtained by them. +Mathematics may be compared to a mill of exquisite workmanship, which +grinds you stuff of any degree of fineness; but, nevertheless, what you +get out depends upon what you put in; and as the grandest mill in the +world will not extract wheat-flour from peascods, so pages of formulae +will not get a definite result out of loose data. + +In the present instance it appears to be admitted:-- + +1. That it is not absolutely certain, after all, whether the moon's mean +motion is undergoing acceleration, or the earth's rotation +retardation.[20] And yet this is the key of the whole position. + +[Footnote 20: It will be understood that I do not wish to deny that the +earth's rotation _may be_ undergoing retardation.] + +2. If the rapidity of the earth's rotation is diminishing, it is not +certain how much of that retardation is due to tidal friction, how much +to meteors, how much to possible excess of melting over accumulation of +polar ice, during the period covered by observation, which amounts, at +the outside, to not more than 2,600 years. + +3. The effect of a different distribution of land and water in modifying +the retardation caused by tidal friction, and of reducing it, under some +circumstances, to a minimum, does not appear to be taken into account. + +4. During the Miocene epoch the polar ice was certainly many feet thinner +than it has been during, or since, the Glacial epoch. Sir W. Thomson +tells us that the accumulation of something more than a foot of ice +around the poles (which implies the withdrawal of, say, an inch of water +from the general surface of the sea) will cause the earth to rotate +quicker by one-tenth of a second per annum. It would appear, therefore, +that the earth may have been rotating, throughout the whole period which +has elapsed from the commencement of the Glacial epoch down to the +present time, one, or more, seconds per annum quicker than it rotated +during the Miocene epoch. + +But, according to Sir W. Thomson's calculation, tidal retardation will +only account for a retardation of 22" in a century, or 22/100 (say 1/5) +of a second per annum. + +Thus, assuming that the accumulation of polar ice since the Miocene epoch +has only been sufficient to produce ten times the effect of a coat of ice +one foot thick, we shall have an accelerating cause which covers all the +loss from tidal action, and leaves a balance of 4/5 of a second per annum +in the way of acceleration. + +If tidal retardation can be thus checked and overthrown by other +temporary conditions, what becomes of the confident assertion, based upon +the assumed uniformity of tidal retardation, that ten thousand million +years ago the earth must have been rotating more than twice as fast as at +present, and, therefore, that we geologists are "in direct opposition to +the principles of Natural Philosophy" if we spread geological history +over that time? + +II. The second argument is thus stated by Sir W. Thomson:--"An article, +by myself, published in 'Macmillan's Magazine' for March 1862, on the age +of the sun's heat, explains results of investigation into various +questions as to possibilities regarding the amount of heat that the sun +could have, dealing with it as you would with a stone, or a piece of +matter, only taking into account the sun's dimensions, which showed it to +be possible that the sun may have already illuminated the earth for as +many as one hundred million years, but at the same time rendered it +almost certain that he had not illuminated the earth for five hundred +millions of years. The estimates here are necessarily very vague; but +yet, vague as they are, I do not know that it is possible, upon any +reasonable estimate founded on known properties of matter, to say that we +can believe the sun has really illuminated the earth for five hundred +million years."[21] + +[Footnote 21: _Loc. cit._ p. 20.] + +I do not wish to "Hansardise" Sir William Thomson by laying much stress +on the fact that, only fifteen years ago he entertained a totally +different view of the origin of the sun's heat, and believed that the +energy radiated from year to year was supplied from year to year--a +doctrine which would have suited Hutton perfectly. But the fact that so +eminent a physical philosopher has, thus recently, held views opposite to +those which he now entertains, and that he confesses his own estimates to +be "very vague," justly entitles us to disregard those estimates, if any +distinct facts on our side go against them. However, I am not aware that +such facts exist. As I have already said, for anything I know, one, two, +or three hundred millions of years may serve the needs of geologists +perfectly well. + +III. The third line of argument is based upon the temperature of the +interior of the earth. Sir W. Thomson refers to certain investigations +which prove that the present thermal condition of the interior of the +earth implies either a heating of the earth within the last 20,000 years +of as much as 100 deg. F., or a greater heating all over the surface at some +time further back than 20,000 years, and then proceeds thus:-- + +"Now, are geologists prepared to admit that, at some time within the last +20,000 years, there has been all over the earth so high a temperature as +that? I presume not; no geologist--no _modern_ geologist--would for a +moment admit the hypothesis that the present state of underground heat is +due to a heating of the surface at so late a period as 20,000 years ago. +If that is not admitted we are driven to a greater heat at some time more +than 20,000 years ago. A greater heating all over the surface than 100 deg. +Fahrenheit would kill nearly all existing plants and animals, I may +safely say. Are modern geologists prepared to say that all life was +killed off the earth 50,000, 100,000, or 200,000 years ago? For the +uniformity theory, the further back the time of high surface-temperature +is put the better; but the further back the time of heating, the hotter +it must have been. The best for those who draw most largely on time is +that which puts it furthest back; and that is the theory that the heating +was enough to melt the whole. But even if it was enough to melt the +whole, we must still admit some limit, such as fifty million years, one +hundred million years, or two or three hundred million years ago. Beyond +that we cannot go."[22] + +[Footnote 22: _Loc. cit._ p. 24.] + +It will be observed that the "limit" is once again of the vaguest, +ranging from 50,000,000 years to 300,000,000. And the reply is, once +more, that, for anything that can be proved to the contrary, one or two +hundred million years might serve the purpose, even of a thoroughgoing +Huttonian uniformitarian, very well. + +But if, on the other hand, the 100,000,000 or 200,000,000 years appear to +be insufficient for geological purposes, we must closely criticise the +method by which the limit is reached. The argument is simple enough. +_Assuming_ the earth to be nothing but a cooling mass, the quantity of +heat lost per year, _supposing_ the rate of cooling to have been uniform, +multiplied by any given number of years, will be given the minimum +temperature that number of years ago. + +But is the earth nothing but a cooling mass, "like a hot-water jar such +as is used in carriages," or "a globe of sandstone," and has its cooling +been uniform? An affirmative answer to both these questions seems to be +necessary to the validity of the calculations on which Sir W. Thomson +lays so much stress. + +Nevertheless it surely may be urged that such affirmative answers are +purely hypothetical, and that other suppositions have an equal right to +consideration. + +For example, is it not possible that, at the prodigious temperature which +would seem to exist at 100 miles below the surface, all the metallic +bases may behave as mercury does at a red heat, when it refuses to +combine with oxygen; while, nearer the surface, and therefore at a lower +temperature, they may enter into combination (as mercury does with oxygen +a few degrees below its boiling-point), and so give rise to a heat +totally distinct from that which they possess as cooling bodies? And has +it not also been proved by recent researches that the quality of the +atmosphere may immensely affect its permeability to heat; and, +consequently, profoundly modify the rate of cooling the globe as a whole? + +I do not think it can be denied that such conditions may exist, and may +so greatly affect the supply, and the loss, of terrestrial heat as to +destroy the value of any calculations which leave them out of sight. + +My functions as your advocate are at an end. I speak with more than the +sincerity of a mere advocate when I express the belief that the case +against us has entirely broken down. The cry for reform which has been +raised without, is superfluous, inasmuch as we have long been reforming +from within, with all needful speed. And the critical examination of the +grounds upon which the very grave charge of opposition to the principles +of Natural Philosophy has been brought against us, rather shows that we +have exercised a wise discrimination in declining, for the present, to +meddle with our foundations. + + + +XI + + +PALAEONTOLOGY AND THE DOCTRINE OF EVOLUTION + +[1870] + +It is now eight years since, in the absence of the late Mr. Leonard +Horner, who then presided over us, it fell to my lot, as one of the +Secretaries of this Society, to draw up the customary Annual Address. I +availed myself of the opportunity to endeavour to "take stock" of that +portion of the science of biology which is commonly called +"palaeontology," as it then existed; and, discussing one after another the +doctrines held by palaeontologists, I put before you the results of my +attempts to sift the well-established from the hypothetical or the +doubtful. Permit me briefly to recall to your minds what those results +were:-- + +1. The living population of all parts of the earth's surface which have +yet been examined has undergone a succession of changes which, upon the +whole, have been of a slow and gradual character. + +2. When the fossil remains which are the evidences of these successive +changes, as they have occurred in any two more or less distant parts of +the surface of the earth, are compared, they exhibit a certain broad and +general parallelism. In other words, certain forms of life in one +locality occur in the same general order of succession as, or are +_homotaxial_ with, similar forms in the other locality. + +3. Homotaxis is not to be held identical with synchronism without +independent evidence. It is possible that similar, or even identical, +faunae and florae in two different localities may be of extremely different +ages, if the term "age" is used in its proper chronological sense. I +stated that "geographical provinces, or zones, may have been as +distinctly marked in the Palaeozoic epoch as at present; and those +seemingly sudden appearances of new genera and species which we ascribe +to new creation, may be simple results of migration." + +4. The opinion that the oldest known fossils are the earliest forms of +life has no solid foundation. + +5. If we confine ourselves to positively ascertained facts, the total +amount of change in the forms of animal and vegetable life, since the +existence of such forms is recorded, is small. When compared with the +lapse of time since the first appearance of these forms, the amount of +change is wonderfully small. Moreover, in each great group of the animal +and vegetable kingdoms, there are certain forms which I termed PERSISTENT +TYPES, which have remained, with but very little apparent change, from +their first appearance to the present time. + +6. In answer to the question "What, then, does an impartial survey of the +positively ascertained truths of palaeontology testify in relation to the +common doctrines of progressive modification, which suppose that +modification to have taken place by a necessary progress from more to +less embryonic forms, from more to less generalised types, within the +limits of the period represented by the fossiliferous rocks?" I reply, +"It negatives these doctrines; for it either shows us no evidence of such +modification, or demonstrates such modification as has occurred to have +been very slight; and, as to the nature of that modification, it yields +no evidence whatsoever that the earlier members of any long-continued +group were more generalised in structure than the later ones." + +I think that I cannot employ my last opportunity of addressing you, +officially, more properly--I may say more dutifully--than in revising +these old judgments with such help as further knowledge and reflection, +and an extreme desire to get at the truth, may afford me. + +1. With respect to the first proposition, I may remark that whatever may +be the case among the physical geologists, catastrophic palaeontologists +are practically extinct. It is now no part of recognised geological +doctrine that the species of one formation all died out and were replaced +by a brand-new set in the next formation. On the contrary, it is +generally, if not universally, agreed that the succession of life has +been the result of a slow and gradual replacement of species by species; +and that all appearances of abruptness of change are due to breaks in the +series of deposits, or other changes in physical conditions. The +continuity of living forms has been unbroken from the earliest times to +the present day. + +2, 3. The use of the word "homotaxis" instead of "synchronism" has not, +so far as I know, found much favour in the eyes of geologists. I hope, +therefore, that it is a love for scientific caution, and not mere +personal affection for a bantling of my own, which leads me still to +think that the change of phrase is of importance, and that the sooner it +is made, the sooner shall we get rid of a number of pitfalls which beset +the reasoner upon the facts and theories of geology. + +One of the latest pieces of foreign intelligence which has reached us is +the information that the Austrian geologists have, at last, succumbed to +the weighty evidence which M. Barrande has accumulated, and have admitted +the doctrine of colonies. But the admission of the doctrine of colonies +implies the further admission that even identity of organic remains is no +proof of the synchronism of the deposits which contain them. + +4. The discussions touching the _Eozoon,_ which commenced in 1864, have +abundantly justified the fourth proposition. In 1862, the oldest record +of life was in the Cambrian rocks; but if the _Eozoon_ be, as Principal +Dawson and Dr. Carpenter have shown so much reason for believing, the +remains of a living being, the discovery of its true nature carried life +back to a period which, as Sir William Logan has observed, is as remote +from that during which the Cambrian rocks were deposited, as the Cambrian +epoch itself is from the tertiaries. In other words, the ascertained +duration of life upon the globe was nearly doubled at a stroke. + +5. The significance of persistent types, and of the small amount of +change which has taken place even in those forms which can be shown to +have been modified, becomes greater and greater in my eyes, the longer I +occupy myself with the biology of the past. + +Consider how long a time has elapsed since the Miocene epoch. Yet, at +that time there is reason to believe that every important group in every +order of the _Mammalia_ was represented. Even the comparatively scanty +Eocene fauna yields examples of the orders _Cheiroptera, Insectivora, +Rodentia_, and _Perissodactyla_; of _Artiodactyla_ under both the +Ruminant and the Porcine modifications; of _Caranivora, Cetacea_, and +_Marsupialia_. + +Or, if we go back to the older half of the Mesozoic epoch, how truly +surprising it is to find every order of the _Reptilia_, except the +_Ophidia_, represented; while some groups, such as the _Ornithoseclida_ +and the _Pterosauria_, more specialised than any which now exist, +abounded. + +There is one division of the _Amphibia_ which offers especially important +evidence upon this point, inasmuch as it bridges over the gap between the +Mesozoic and the Palaeozoic formations (often supposed to be of such +prodigious magnitude), extending, as it does, from the bottom of the +Carboniferous series to the top of the Trias, if not into the Lias. I +refer to the Labyrinthodonts. As the Address of 1862 was passing through +the press, I was able to mention, in a note, the discovery of a large +Labyrinthodont, with well-ossified vertebrae, in the Edinburgh coal-field. +Since that time eight or ten distinct genera of Labyrinthodonts have been +discovered in the Carboniferous rocks of England, Scotland, and Ireland, +not to mention the American forms described by Principal Dawson and +Professor Cope. So that, at the present time, the Labyrinthodont Fauna of +the Carboniferous rocks is more extensive and diversified than that of +the Trias, while its chief types, so far as osteology enables us to +judge, are quite as highly organised. Thus it is certain that a +comparatively highly organised vertebrate type, such as that of the +Labyrinthodonts, is capable of persisting, with no considerable change, +through the period represented by the vast deposits which constitute the +Carboniferous, the Permian, and the Triassic formations. + +The very remarkable results which have been brought to light by the +sounding and dredging operations, which have been carried on with such +remarkable success by the expeditions sent out by our own, the American, +and the Swedish Governments, under the supervision of able naturalists, +have a bearing in the same direction. These investigations have +demonstrated the existence, at great depths in the ocean, of living +animals in some cases identical with, in others very similar to, those +which are found fossilised in the white chalk. The _Globigerinoe_, +Cyatholiths, Coccospheres, Discoliths in the one are absolutely identical +with those in the other; there are identical, or closely analogous, +species of Sponges, Echinoderms, and Brachiopods. Off the coast of +Portugal, there now lives a species of _Beryx_, which, doubtless, leaves +its bones and scales here and there in the Atlantic ooze, as its +predecessor left its spoils in the mud of the sea of the Cretaceous +epoch. + +Many years ago[1] I ventured to speak of the Atlantic mud as "modern +chalk," and I know of no fact inconsistent with the view which Professor +Wyville Thomson has advocated, that the modern chalk is not only the +lineal descendant of the ancient chalk, but that it remains, so to speak, +in the possession of the ancestral estate; and that from the Cretaceous +period (if not much earlier) to the present day, the deep sea has covered +a large part of what is now the area of the Atlantic. But if +_Globigerina_, and _Terebratula caput-serpentis_ and _Beryx_, not to +mention other forms of animals and of plants, thus bridge over the +interval between the present and the Mesozoic periods, is it possible +that the majority of other living things underwent a "sea-change into +something new and strange" all at once? + +[Footnote 1: See an article in the _Saturday Review_, for 1858, on +"Chalk, Ancient and Modern."] + +6. Thus far I have endeavoured to expand and to enforce by fresh +arguments, but not to modify in any important respect, the ideas +submitted to you on a former occasion. But when I come to the +propositions touching progressive modification, it appears to me, with +the help of the new light which has broken from various quarters, that +there is much ground for softening the somewhat Brutus-like severity with +which, in 1862, I dealt with a doctrine, for the truth of which I should +have been glad enough to be able to find a good foundation. So far, +indeed, as the _Invertebrata_ and the lower _Vertebrata_ are concerned, +the facts and the conclusions which are to be drawn from them appear to +me to remain what they were. For anything that, as yet, appears to the +contrary, the earliest known Marsupials may have been as highly organised +as their living congeners; the Permian lizards show no signs of +inferiority to those of the present day; the Labyrinthodonts cannot be +placed below the living Salamander and Triton; the Devonian Ganoids are +closely related to _Polypterus_ and to _Lepidosiren_. + +But when we turn to the higher _Vertebrata_, the results of recent +investigations, however we may sift and criticise them, seem to me to +leave a clear balance in favour of the doctrine of the evolution of +living forms one from another. Nevertheless, in discussing this question, +it is very necessary to discriminate carefully between the different +kinds of evidence from fossil remains which are brought forward in favour +of evolution. + +Every fossil which takes an intermediate place between forms of life +already known, may be said, so far as it is intermediate, to be evidence +in favour of evolution, inasmuch as it shows a possible road by which +evolution may have taken place. But the mere discovery of such a form +does not, in itself, prove that evolution took place by and through it, +nor does it constitute more than presumptive evidence in favour of +evolution in general. Suppose A, B, C to be three forms, while B is +intermediate in structure between A and C. Then the doctrine of evolution +offers four possible alternatives. A may have become C by way of B; or C +may have become A by way of B; or A and C may be independent +modifications of B; or A, B, and C may be independent modifications of +some unknown D. Take the case of the Pigs, the _Anoplothcridoe_, and the +Ruminants. The _Anoplothcridoe_ are intermediate between the first and +the last; but this does not tell us whether the Ruminants have come from +the Pigs, or the Pigs from Ruminants, or both from _Anoplothcridoe_, or +whether Pigs, Ruminants, and _Anoplotlicridoe_ alike may not have +diverged from some common stock. + +But if it can be shown that A, B, and C exhibit successive stages in the +degree of modification, or specialisation, of the same type; and if, +further, it can be proved that they occur in successively newer deposits, +A being in the oldest and C in the newest, then the intermediate +character of B has quite another importance, and I should accept it, +without hesitation, as a link in the genealogy of C. I should consider +the burden of proof to be thrown upon any one who denied C to have been +derived from A by way of B, or in some closely analogous fashion; for it +is always probable that one may not hit upon the exact line of filiation, +and, in dealing with fossils, may mistake uncles and nephews for fathers +and sons. + +I think it necessary to distinguish between the former and the latter +classes of intermediate forms, as _intercalary types_ and _linear types_. +When I apply the former term, I merely mean to say that as a matter of +fact, the form B, so named, is intermediate between the others, in the +sense in which the _Anoplotherium_ is intermediate between the Pigs and +the Ruminants--without either affirming, or denying, any direct genetic +relation between the three forms involved. When I apply the latter term, +on the other hand, I mean to express the opinion that the forms A, B, and +C constitute a line of descent, and that B is thus part of the lineage of +C. + +From the time when Cuvier's wonderful researches upon the extinct Mammals +of the Paris gypsum first made intercalary types known, and caused them +to be recognised as such, the number of such forms has steadily increased +among the higher _Mammalia_. Not only do we now know numerous intercalary +forins of _Ungulata_, but M. Gaudry's great monograph upon the fossils of +Pikermi (which strikes me as one of the most perfect pieces of +palaeontological work I have seen for a long time) shows us, among the +Primates, _Mesopithecus_ as an intercalary form between the +_Semnopitheci_ and the _Macaci_; and among the _Carnivora_, _Hyoenictis_ +and _Ictitherium_ as intercalary, or, perhaps, linear types between the +_Viverridoe_ and the _Hyoenidoe_. + +Hardly any order of the higher _Mammalia_ stands so apparently separate +and isolated from the rest as that of the _Cetacea_; though a careful +consideration of the structure of the pinnipede _Carnivora_, or Seals, +shows, in them, many an approximation towards the still more completely +marine mammals. The extinct _Zeuglodon_, however, presents us with an +intercalary form between the type of the Seals and that of the Whales. +The skull of this great Eocene sea-monster, in fact, shows by the narrow +and prolonged interorbital region; the extensive union of the parietal +bones in a sagittal suture; the well-developed nasal bones; the distinct +and large incisors implanted in premaxillary bones, which take a full +share in bounding the fore part of the gape; the two-fanged molar teeth +with triangular and serrated crowns, not exceeding five on each side in +each jaw; and the existence of a deciduous dentition--its close relation +with the Seals. While, on the other hand, the produced rostral form of +the snout, the long symphysis, and the low coronary process of the +mandible are approximations to the cetacean form of those parts. + +The scapula resembles that of the cetacean _Hyperoodon_, but the supra- +spinous fossa is larger and more seal-like; as is the humerus, which +differs from that of the _Cetacea_ in presenting true articular surfaces +for the free jointing of the bones of the fore-arm. In the apparently +complete absence of hinder limbs, and in the characters of the vertebral +column, the _Zeuglodon_ lies on the cetacean side of the boundary line; +so that upon the whole, the Zeuglodonts, transitional as they are, are +conveniently retained in the cetacean order. And the publication, in +1864, of M. Van Beneden's memoir on the Miocene and Pliocene _Squalodon_, +furnished much better means than anatomists previously possessed of +fitting in another link of the chain which connects the existing +_Cetacea_ with _Zeuglodon_. The teeth are much more numerous, although +the molars exhibit the zeuglodont double fang; the nasal bones are very +short, and the upper surface of the rostrum presents the groove, filled +up during life by the prolongation of the ethmoidal cartilage, which is +so characteristic of the majority of the _Cetacea_. + +It appears to me that, just as among the existing _Carnivora_, the +walruses and the eared seals are intercalary forms between the fissipede +Carnivora and the ordinary seals, so the Zeuglodonts are intercalary +between the _Carnivora_, as a whole, and the _Cetacea_. Whether the +Zeuglodonts are also linear types in their relation to these two groups +cannot be ascertained, until we have more definite knowledge than we +possess at present, respecting the relations in time of the _Carnivora_ +and _Cetacea_. + +Thus far we have been concerned with the intercalary types which occupy +the intervals between Families or Orders of the same class; but the +investigations which have been carried on by Professor Gegenbaur, +Professor Cope, and myself into the structure and relations of the +extinct reptilian forms of the _Ornithoscelida_ (or _Dinosauria_ and +_Compsognatha_) have brought to light the existence of intercalary forms +between what have hitherto been always regarded as very distinct classes +of the vertebrate sub-kingdom, namely _Reptilia_ and _Aves_. Whatever +inferences may, or may not, be drawn from the fact, it is now an +established truth that, in many of these _Ornithoscelida_, the hind limbs +and the pelvis are much more similar to those of Birds than they are to +those of Reptiles, and that these Bird-reptiles, or Reptile-birds, were +more or less completely bipedal. + +When I addressed you in 1862, I should have been bold indeed had I +suggested that palaeontology would before long show us the possibility of +a direct transition from the type of the lizard to that of the ostrich. +At the present moment, we have, in the _Ornithoscelida_, the intercalary +type, which proves that transition to be something more than a +possibility; but it is very doubtful whether any of the genera of +_Ornithoscelida_ with which we are at present acquainted are the actual +linear types by which the transition from the lizard to the bird was +effected. These, very probably, are still hidden from us in the older +formations. + +Let us now endeavour to find some cases of true linear types, or forms +which are intermediate between others because they stand in a direct +genetic relation to them. It is no easy matter to find clear and +unmistakable evidence of filiation among fossil animals; for, in order +that such evidence should be quite satisfactory, it is necessary that we +should be acquainted with all the most important features of the +organisation of the animals which are supposed to be thus related, and +not merely with the fragments upon which the genera and species of the +palaeontologist are so often based. M. Gaudry has arranged the species of +_Hyoenidoe, Proboscidea, Rhinocerotidoe_, and _Equidoe_ in their order of +filiation from their earliest appearance in the Miocene epoch to the +present time, and Professor Ruetimeyer has drawn up similar schemes for +the Oxen and other _Ungulata_--with what, I am disposed to think, is a +fair and probable approximation to the order of nature. But, as no one is +better aware than these two learned, acute, and philosophical biologists, +all such arrangements must be regarded as provisional, except in those +cases in which, by a fortunate accident, large series of remains are +obtainable from a thick and widespread series of deposits. It is easy to +accumulate probabilities--hard to make out some particular case in such a +way that it will stand rigorous criticism. + +After much search, however, I think that such a case is to be made out in +favour of the pedigree of the Horses. + +The genus _Equus_ is represented as far back as the latter part of the +Miocene epoch; but in deposits belonging to the middle of that epoch its +place is taken by two other genera, _Hipparion_ and _Anchitherium_;[2] +and, in the lowest Miocene and upper Eocene, only the last genus occurs. +A species of _Anchitherium_ was referred by Cuvier to the _Paloeotheria_ +under the name of _P. aurelianense_. The grinding-teeth are in fact very +similar in shape and in pattern, and in the absence of any thick layer of +cement, to those of some species of _Paloeotherium_, especially Cuvier's +_Paloeotherium minus_, which has been formed into a separate genus, +_Plagiolophus_, by Pomel. But in the fact that there are only six full- +sized grinders in the lower jaw, the first premolar being very small; +that the anterior grinders are as large as, or rather larger than, the +posterior ones; that the second premolar has an anterior prolongation; +and that the posterior molar of the lower jaw has, as Cuvier pointed out, +a posterior lobe of much smaller size and different form, the dentition +of _Anchitherium_ departs from the type of the _Paloeotherium_, and +approaches that of the Horse. + +[Footnote 2: Hermann von Meyer gave the name of _Anchitherium_ to _A. +Ezquerroe_; and in his paper on the subject he takes great pains to +distinguish the latter as the type of a new genus, from Cuvier's +_Paloeotherium d'Orleans_. But it is precisely the _Paloeotherium +d'Orleans_ which is the type of Christol's genus _Hipparitherium_; and +thus, though _Hipparitherium_ is of later date than _Anchitherium_, it +seemed to me to have a sort of equitable right to recognition when this +Address was written. On the whole, however, it seems most convenient to +adopt _Anchitherium_.] + +Again, the skeleton of _Anchitherium_ is extremely equine. M. Christol +goes so far as to say that the description of the bones of the horse, or +the ass, current in veterinary works, would fit those of _Anchitherium_. +And, in a general way, this may be true enough; but there are some most +important differences, which, indeed, are justly indicated by the same +careful observer. Thus the ulna is complete throughout, and its shaft is +not a mere rudiment, fused into one bone with the radius. There are three +toes, one large in the middle and one small on each side. The femur is +quite like that of a horse, and has the characteristic fossa above the +external condyle. In the British Museum there is a most instructive +specimen of the leg-bones, showing that the fibula was represented by the +external malleolus and by a flat tongue of bone, which extends up from it +on the outer side of the tibia, and is closely ankylosed with the latter +bone.[3] The hind toes are three, like those of the fore leg; and the +middle metatarsal bone is much less compressed from side to side than +that of the horse. + +[Footnote 3: I am indebted to M. Gervais for a specimen which indicates +that the fibula was complete, at any rate, in some cases; and for a very +interesting ramps of a mandible, which shows that, as in the +_Paloeotheria_, the hindermost milk-molar of the lower jaw was devoid of +the posterior lobe which exists in the hindermost true molar.] + +In the _Hipparion_, the teeth nearly resemble those of the Horses, though +the crowns of the grinders are not so long; like those of the Horses, +they are abundantly coated with cement. The shaft of the ulna is reduced +to a mere style, ankylosed throughout nearly its whole length with the +radius, and appearing to be little more than a ridge on the surface of +the latter bone until it is carefully examined. The front toes are still +three, but the outer ones are more slender than in _Anchitherium_, and +their hoofs smaller in proportion to that of the middle toe; they are, in +fact, reduced to mere dew-claws, and do not touch the ground. In the leg, +the distal end of the fibula is so completely united with the tibia that +it appears to be a mere process of the latter bone, as in the Horses. + +In _Equus_, finally, the crowns of the grinding-teeth become longer, and +their patterns are slightly modified; the middle of the shaft of the ulna +usually vanishes, and its proximal and distal ends ankylose with the +radius. The phalanges of the two outer toes in each foot disappear, their +metacarpal and metatarsal bones being left as the "splints." + +The _Hipparion_ has large depressions on the face in front of the orbits, +like those for the "larmiers" of many ruminants; but traces of these are +to be seen in some of the fossil horses from the Sewalik Hills; and, as +Leidy's recent researches show, they are preserved in _Anchitherium_. + +When we consider these facts, and the further circumstance that the +Hipparions, the remains of which have been collected in immense numbers, +were subject, as M. Gaudry and others have pointed out, to a great range +of variation, it appears to me impossible to resist the conclusion that +the types of the _Anchitherium_, of the _Hipparion_, and of the ancient +Horses constitute the lineage of the modern Horses, the _Hipparion_ being +the intermediate stage between the other two, and answering to B in my +former illustration. + +The process by which the _Anchitherium_ has been converted into _Equus_ +is one of specialisation, or of more and more complete deviation from +what might be called the average form of an ungulate mammal. In the +Horses, the reduction of some parts of the limbs, together with the +special modification of those which are left, is carried to a greater +extent than in any other hoofed mammals. The reduction is less and the +specialisation is less in the _Hipparion_, and still less in the +_Anchitherium_; but yet, as compared with other mammals, the reduction +and specialisation of parts in the _Anchitherium_ remain great. + +Is it not probable then, that, just as in the Miocene epoch, we find an +ancestral equine form less modified than _Equus_, so, if we go back to +the Eocene epoch, we shall find some quadruped related to the +_Anchitherium_, as _Hipparion_ is related to _Equus_, and consequently +departing less from the average form? + +I think that this desideratum is very nearly, if not quite, supplied by +_Plagiolophus_, remains of which occur abundantly in some parts of the +Upper and Middle Eocene formations. The patterns of the grinding-teeth of +_Plagiolophus_ are similar to those of _Anchitherium_, and their crowns +are as thinly covered with cement; but the grinders diminish in size +forwards, and the last lower molar has a large hind lobe, convex outwards +and concave inwards, as in _Palueotherium_. The ulna is complete and much +larger than in any of the _Equidoe_, while it is more slender than in +most of the true _Paloeotheria_; it is fixedly united, but not ankylosed, +with the radius. There are three toes in the fore limb, the outer ones +being slender, but less attenuated than in the _Equidoe_. The femur is +more like that of the _Paloeotheria_ than that of the horse, and has only +a small depression above its outer condyle in the place of the great +fossa which is so obvious in the _Equidoe_. The fibula is distinct, but +very slender, and its distal end is ankylosed with the tibia. There are +three toes on the hind foot having similar proportions to those on the +fore foot. The principal metacarpal and metatarsal bones are flatter than +they are in any of the _Equidoe_; and the metacarpal bones are longer +than the metatarsals, as in the _Paloeotheria_. + +In its general form, _Plagiolophus_ resembles a very small and slender +horse,[4] and is totally unlike the reluctant, pig-like creature depicted +in Cuvier's restoration of his _Paloeotherium minus_ in the "Ossemens +Fossiles." + +[Footnote 4: Such, at least, is the conclusion suggested by the +proportions of the skeleton figured by Cuvier and De Blainville; but +perhaps something between a Horse and an Agouti would be nearest the +mark.] + +It would be hazardous to say that _Plagiolophus_ is the exact radical +form of the Equine quadrupeds; but I do not think there can be any +reasonable doubt that the latter animals have resulted from the +modification of some quadruped similar to _Plagiolophus_. + +We have thus arrived at the Middle Eocene formation, and yet have traced +back the Horses only to a three-toed stock; but these three-toed forms, +no less than the Equine quadrupeds themselves, present rudiments of the +two other toes which appertain to what I have termed the "average" +quadruped. If the expectation raised by the splints of the Horses that, +in some ancestor of the Horses, these splints would be found to be +complete digits, has been verified, we are furnished with very strong +reasons for looking for a no less complete verification of the +expectation that the three-toed _Plagiolophus_-like "avus" of the horse +must have had a five-toed "atavus" at some earlier period. + +No such five-toed "atavus," however, has yet made its appearance among +the few middle and older Eocene _Mammalia_ which are known. + +Another series of closely affiliated forms, though the evidence they +afford is perhaps less complete than that of the Equine series, is +presented to us by the _Dichobune_ of the Eocene epoch, the +_Cainotherium_ of the Miocene, and the _Tragulidoe_, or so-called "Musk- +deer," of the present day. + +The _Tragulidoe_; have no incisors in the upper jaw, and only six +grinding-teeth on each side of each jaw; while the canine is moved up to +the outer incisor, and there is a diastema in the lower jaw. There are +four complete toes on the hind foot, but the middle metatarsals usually +become, sooner or later, ankylosed into a cannon bone. The navicular and +the cuboid unite, and the distal end of the fibula is ankylosed with the +tibia. + +In _Cainotherium_ and _Dichobune_ the upper incisors are fully developed. +There are seven grinders; the teeth form a continuous series without a +diastema. The metatarsals, the navicular and cuboid, and the distal end +of the fibula, remain free. In the _Cainotherium_, also, the second +metacarpal is developed, but is much shorter than the third, while the +fifth is absent or rudimentary. In this respect it resembles +_Anoplotherium secundarium_. This circumstance, and the peculiar pattern +of the upper molars in _Cainotherium_, lead me to hesitate in considering +it as the actual ancestor of the modern _Tragulidoe_. If _Dichobune_ has +a fore-toed fore foot (though I am inclined to suspect that it resembles +_Cainotherium_), it will be a better representative of the oldest forms +of the Traguline series; but _Dichobune_ occurs in the Middle Eocene, and +is, in fact, the oldest known artiodactyle mammal. Where, then, must we +look for its five-toed ancestor? + +If we follow down other lines of recent and tertiary _Ungulata_, the same +question presents itself. The Pigs are traceable back through the Miocene +epoch to the Upper Eocene, where they appear in the two well-marked forms +of _Hyopopotamus_ and _Choeropotamus_; but _Hyopotamus_ appears to have +had only two toes. + +Again, all the great groups of the Ruminants, the _Bovidoe, Antilopidoe, +Camelopardalidoe_, and _Cervidoe_, are represented in the Miocene epoch, +and so are the Camels. The Upper Eocene _Anoplotherium_, which is +intercalary between the Pigs and the _Tragulidoe_, has only two, or, at +most, three toes. Among the scanty mammals of the Lower Eocene formation +we have the perissodactyle _Ungulata_ represented by _Coryphodon, +Hyracotherium_, and _Pliolophus_. Suppose for a moment, for the sake of +following out the argument, that _Pliolophus_ represents the primary +stock of the Perissodactyles, and _Dichobune_ that of the Artiodactyles +(though I am far from saying that such is the case), then we find, in the +earliest fauna of the Eocene epoch to which our investigations carry us, +the two divisions of the _Ungulata_ completely differentiated, and no +trace of any common stock of both, or of five-toed predecessors to +either. With the case of the Horses before us, justifying a belief in the +production of new animal forms by modification of old ones, I see no +escape from the necessity of seeking for these ancestors of the +_Ungulata_ beyond the limits of the Tertiary formations. + +I could as soon admit special creation, at once, as suppose that the +Perissodactyles and Artiodactyles had no five-toed ancestors. And when we +consider how large a portion of the Tertiary period elapsed before +_Anchitherium_ was converted into _Equus_, it is difficult to escape the +conclusion that a large proportion of time anterior to the Tertiary +period must have been expended in converting the common stock of the +_Ungulata_ into Perissodactyles and Artiodactyles. + +The same moral is inculcated by the study of every other order of +Tertiary monodelphous _Mammalia_. Each of these orders is represented in +the Miocene epoch: the Eocene formation, as I have already said, contains +_Cheiroptera, Insectivora, Rodentia, Ungulata, Carnivora_, and _Cetacea_. +But the _Cheiroptera_ are extreme modifications of the _Insectivora_, +just as the _Cetacea_ are extreme modifications of the Carnivorous type; +and therefore it is to my mind incredible that monodelphous _Insectivora_ +and _Carnivora_ should not have been abundantly developed, along with +_Ungulata_, in the Mesozoic epoch. But if this be the case, how much +further back must we go to find the common stock of the monodelphous +_Mammalia_? As to the _Didelphia_, if we may trust the evidence which +seems to be afforded by their very scanty remains, a Hypsiprymnoid form +existed at the epoch of the Trias, contemporaneously with a Carnivorous +form. At the epoch of the Trias, therefore, the _Marsupialia_ must have +already existed long enough to have become differentiated into +carnivorous and herbivorous forms. But the _Monotremata_ are lower forms +than the _Didelphia_ which last are intercalary between the +_Ornithodelphia_ and the _Monodelphia_. To what point of the Palaeozoic +epoch, then, must we, upon any rational estimate, relegate the origin of +the _Monotremata?_ + +The investigation of the occurrence of the classes and of the orders of +the _Sauropsida_ in time points in exactly the same direction. If, as +there is great reason to believe, true Birds existed in the Triassic +epoch, the ornithoscelidous forms by which Reptiles passed into Birds +must have preceded them. In fact there is, even at present, considerable +ground for suspecting the existence of _Dinosauria_ in the Permian +formations; but, in that case, lizards must be of still earlier date. And +if the very small differences which are observable between the +_Crocodilia_ of the older Mesozoic formations and those of the present +day furnish any sort of approximation towards an estimate of the average +rate of change among the _Sauropsida_, it is almost appalling to reflect +how far back in Palaeozoic times we must go, before we can hope to arrive +at that common stock from which the _Crocodilia, Lacertilia, +Ornithoscelida_, and _Plesiosauria_, which had attained so great a +development in the Triassic epoch, must have been derived. + +The _Amphibia_ and _Pisces_ tell the same story. There is not a single +class of vertebrated animals which, when it first appears, is represented +by analogues of the lowest known members of the same class. Therefore, if +there is any truth in the doctrine of evolution, every class must be +vastly older than the first record of its appearance upon the surface of +the globe. But if considerations of this kind compel us to place the +origin of vertebrated animals at a period sufficiently distant from the +Upper Silurian, in which the first Elasmobranchs and Ganoids occur, to +allow of the evolution of such fishes as these from a Vertebrate as +simple as the _Amphioxus,_ I can only repeat that it is appalling to +speculate upon the extent to which that origin must have preceded the +epoch of the first recorded appearance of vertebrate life. + + +Such is the further commentary which I have to offer upon the statement +of the chief results of palaeontology which I formerly ventured to lay +before you. + +But the growth of knowledge in the interval makes me conscious of an +omission of considerable moment in that statement, inasmuch as it +contains no reference to the bearings of palaeontology upon the theory of +the distribution of life; nor takes note of the remarkable manner in +which the facts of distribution, in present and past times, accord with +the doctrine of evolution, especially in regard to land animals. + +That connection between palaeontology and geology and the present +distribution of terrestrial animals, which so strikingly impressed Mr. +Darwin, thirty years ago, as to lead him to speak of a "law of succession +of types," and of the wonderful relationship on the same continent +between the dead and the living, has recently received much elucidation +from the researches of Gaudry, of Rutimeyer, of Leidy, and of Alphonse +Milne-Edwards, taken in connection with the earlier labours of our +lamented colleague Falconer; and it has been instructively discussed in +the thoughtful and ingenious work of Mr. Andrew Murray "On the +Geographical Distribution of Mammals."[5] + +[Footnote 5: The paper "On the Form and Distribution of the Landtracts +during the Secondary and Tertiary Periods respectively; and on the Effect +upon Animal Life which great Changes in Geographical Configuration have +probably produced," by Mr. Searles V. Wood, jun., which was published in +the _Philosophical Magazine_, in 1862, was unknown to me when this +Address was written. It is well worthy of the most careful study.] + +I propose to lay before you, as briefly as I can, the ideas to which a +long consideration of the subject has given rise in my mind. + +If the doctrine of evolution is sound, one of its immediate consequences +clearly is, that the present distribution of life upon the globe is the +product of two factors, the one being the distribution which obtained in +the immediately preceding epoch, and the other the character and the +extent of the changes which have taken place in physical geography +between the one epoch and the other; or, to put the matter in another +way, the Fauna and Flora of any given area, in any given epoch, can +consist only of such forms of life as are directly descended from those +which constituted the Fauna and Flora of the same area in the immediately +preceding epoch, unless the physical geography (under which I include +climatal conditions) of the area has been so altered as to give rise to +immigration of living forms from some other area. + +The evolutionist, therefore, is bound to grapple with the following +problem whenever it is clearly put before him:--Here are the Faunae of the +same area during successive epochs. Show good cause for believing either +that these Faunae have been derived from one another by gradual +modification, or that the Faunae have reached the area in question by +migration from some area in which they have undergone their development. + +I propose to attempt to deal with this problem, so far as it is +exemplified by the distribution of the terrestrial _Vertebrata_, and I +shall endeavour to show you that it is capable of solution in a sense +entirely favourable to the doctrine of evolution. + +I have elsewhere[6] stated at length the reasons which lead me to +recognise four primary distributional provinces for the terrestrial +_Vertebrata_ in the present world, namely,--first, the _Novozelanian_, or +New-Zealand province; secondly, the _Australian_ province, including +Australia, Tasmania, and the Negrito Islands; thirdly, _Austro-Columbia_, +or South America _plus_ North America as far as Mexico; and fourthly, the +rest of the world, or _Arctogoea_, in which province America north of +Mexico constitutes one sub-province, Africa south of the Sahara a second, +Hindostan a third, and the remainder of the Old World a fourth. + +[Footnote 6: "On the Classification and Distribution of the +Alectoromorphoe;" _Proceedings of the Zoological Society_, 1868.] + +Now the truth which Mr. Darwin perceived and promulgated as "the law of +the succession of types" is, that, in all these provinces, the animals +found in Pliocene or later deposits are closely affined to those which +now inhabit the same provinces; and that, conversely, the forms +characteristic of other provinces are absent. North and South America, +perhaps, present one or two exceptions to the last rule, but they are +readily susceptible of explanation. Thus, in Australia, the later +Tertiary mammals are marsupials (possibly with the exception of the Dog +and a Rodent or two, as at present). In Austro-Columbia, the later +Tertiary fauna exhibits numerous and varied forms of Platyrrhine Apes, +Rodents, Cats, Dogs, Stags, _Edentata_, and Opossums; but, as at present, +no Catarrhine Apes, no Lemurs, no _Insectivora_, Oxen, Antelopes, +Rhinoceroses, nor _Didelphia_ other than Opossums. And in the widespread +Arctogaeal province, the Pliocene and later mammals belong to the same +groups as those which now exist in the province. The law of succession of +types, therefore, holds good for the present epoch as compared with its +predecessor. Does it equally well apply to the Pliocene fauna when we +compare it with that of the Miocene epoch? By great good fortune, an +extensive mammalian fauna of the latter epoch has now become known, in +four very distant portions of the Arctogaeal province which do not differ +greatly in latitude. Thus Falconer and Cautley have made known the fauna +of the sub-Himalayas and the Perim Islands; Gaudry that of Attica; many +observers that of Central Europe and France; and Leidy that of Nebraska, +on the eastern flank of the Rocky Mountains. The results are very +striking. The total Miocene fauna comprises many genera and species of +Catarrhine Apes, of Bats, of _Insectivora_; of Arctogaeal types of +_Rodentia_; of _Proboscidea_; of equine, rhinocerotic, and tapirine +quadrupeds; of cameline, bovine, antilopine, cervine, and traguline +Ruminants; of Pigs and Hippopotamuses; of _Viverridoe_ and _Hyoenidoe_ +among other _Carnivora_; with _Edentata_ allied to the Aretogaeal +_Oryeteropus_ and _Manis_, and not to the Austro-Columbian Edentates. The +only type present in the Miocene, but absent in the existing, fauna of +Eastern Arctogaea, is that of the _Didelphidoe_, which, however, remains +in North America. + +But it is very remarkable that while the Miocene fauna of the Arctogaeal +province, as a whole, is of the same character as the existing fauna of +the same province, as a whole, the component elements of the fauna were +differently associated. In the Miocene epoch, North America possessed +Elephants, Horses, Rhinoceroses, and a great number and variety of +Ruminants and Pigs, which are absent in the present indigenous fauna; +Europe had its Apes, Elephants, Rhinoceroses, Tapirs, Musk-deer, +Giraffes, Hyaenas, great Cats, Edentates, and Opossum-like Marsupials, +which have equally vanished from its present fauna; and in Northern +India, the African types of Hippopotamuses, Giraffes, and Elephants were +mixed up with what are now the Asiatic types of the latter, and with +Camels, and Semnopithecine and Pithecine Apes of no less distinctly +Asiatic forms. + +In fact the Miocene mammalian fauna of Europe and the Himalayan regions +contains, associated together, the types which are at present separately +located in the South-African and Indian sub-provinces of Arctogaea. Now +there is every reason to believe, on other grounds, that both Hindostan, +south of the Ganges, and Africa, south of the Sahara, were separated by a +wide sea from Europe and North Asia during the Middle and Upper Eocene +epochs. Hence it becomes highly probable that the well-known +similarities, and no less remarkable differences between the present +Faunae of India and South Africa have arisen in some such fashion as the +following. Some time during the Miocene epoch, possibly when the +Himalayan chain was elevated, the bottom of the nummulitic sea was +upheaved and converted into dry land, in the direction of a line +extending from Abyssinia to the mouth of the Ganges. By this means, the +Dekhan on the one hand, and South Africa on the other, became connected +with the Miocene dry land and with one another. The Miocene mammals +spread gradually over this intermediate dry land; and if the condition of +its eastern and western ends offered as wide contrasts as the valleys of +the Ganges and Arabia do now, many forms which made their way into Africa +must have been different from those which reached the Dekhan, while +others might pass into both these sub-provinces. + +That there was a continuity of dry land between Europe and North America +during the Miocene epoch, appears to me to be a necessary consequence of +the fact that many genera of terrestrial mammals, such as _Castor, +Hystrix, Elephas, Mastodon, Equus, Hipparion, Anchitherium, Rhinoceros, +Cervus, Amphicyon, Hyoenarctos_, and _Machairodus_, are common to the +Miocene formations of the two areas, and have as yet been found (except +perhaps _Anchitherium_) in no deposit of earlier age. Whether this +connection took place by the east, or by the west, or by both sides of +the Old World, there is at present no certain evidence, and the question +is immaterial to the present argument; but, as there are good grounds for +the belief that the Australian province and the Indian and South-African +sub-provinces were separated by sea from the rest of Arctogaea before the +Miocene epoch, so it has been rendered no less probable, by the +investigations of Mr. Carrick Moore and Professor Duncan, that Austro- +Columbia was separated by sea from North America during a large part of +the Miocene epoch. + +It is unfortunate that we have no knowledge of the Miocene mammalian +fauna of the Australian and Austro-Columbian provinces; but, seeing that +not a trace of a Platyrrhine Ape, of a Procyonine Carnivore, of a +characteristically South-American Rodent, of a Sloth, an Armadillo, or an +Ant-eater has yet been found in Miocene deposits of Arctogaea, I cannot +doubt that they already existed in the Miocene Austro-Columbian province. + +Nor is it less probable that the characteristic types of Australian +Mammalia were already developed in that region in Miocene times. + +But Austro-Columbia presents difficulties from which Australia is free; +_Cantelidoe_ and _Tapirdoe_ are now indigenous in South America as they +are in Arctogaea; and, among the Pliocene Austro-Columbian mammals, the +Arctogaeal genera _Equus, Mastodon,_ and _Machairodus_ are numbered. Are +these Postmiocene immigrants, or Praemiocene natives? + +Still more perplexing are the strange and interesting forms _Toxodon, +Macrauchenia, Typotherium_, and a new Anoplotherioid mammal +(_Homalodotherhon_) which Dr. Cunningham sent over to me some time ago +from Patagonia. I confess I am strongly inclined to surmise that these +last, at any rate, are remnants of the population of Austro-Columbia +before the Miocene epoch, and were not derived from Arctogaea by way of +the north and east. + +The fact that this immense fauna of Miocene Arctogaea is now fully and +richly represented only in India and in South Africa, while it is shrunk +and depauperised in North Asia, Europe, and North America, becomes at +once intelligible, if we suppose that India and South Africa had but a +scanty mammalian population before the Miocene immigration, while the +conditions were highly favourable to the new comers. It is to be supposed +that these new regions offered themselves to the Miocene Ungulates, as +South America and Australia offered themselves to the cattle, sheep, and +horses of modern colonists. But, after these great areas were thus +peopled, came the Glacial epoch, during which the excessive cold, to say +nothing of depression and ice-covering, must have almost depopulated all +the northern parts of Arctogaea, destroying all the higher mammalian +forms, except those which, like the Elephant and Rhinoceros, could adjust +their coats to the altered conditions. Even these must have been driven +away from the greater part of the area; only those Miocene mammals which +had passed into Hindostan and into South Africa would escape decimation +by such changes in the physical geography of Arctogaea. And when the +northern hemisphere passed into its present condition, these lost tribes +of the Miocene Fauna were hemmed by the Himalayas, the Sahara, the Red +Sea, and the Arabian deserts, within their present boundaries. + +Now, on the hypothesis of evolution, there is no sort of difficulty in +admitting that the differences between the Miocene forms of the mammalian +Fauna and those which exist at present are the results of gradual +modification; and, since such differences in distribution as obtain are +readily explained by the changes which have taken place in the physical +geography of the world since the Miocene epoch, it is clear that the +result of the comparison of the Miocene and present Faunae is distinctly +in favour of evolution. Indeed I may go further. I may say that the +hypothesis of evolution explains the facts of Miocene, Pliocene, and +Recent distribution, and that no other supposition even pretends to +account for them. It is, indeed, a conceivable supposition that every +species of Rhinoceros and every species of Hyaena, in the long succession +of forms between the Miocene and the present species, was separately +constructed out of dust, or out of nothing, by supernatural power; but +until I receive distinct evidence of the fact, I refuse to run the risk +of insulting any sane man by supposing that he seriously holds such a +notion. + +Let us now take a step further back in time, and inquire into the +relations between the Miocene Fauna and its predecessor of the Upper +Eocene formation. + +Here it is to be regretted that our materials for forming a judgment are +nothing to be compared in point of extent or variety with those which are +yielded by the Miocene strata. However, what we do know of this Upper +Eocene Fauna of Europe gives sufficient positive information to enable us +to draw some tolerably safe inferences. It has yielded representatives of +_Insectivora_, of _Cheiroptera_, of _Rodentia_, of _Carnivora_, of +artiodactyle and perissodactyle _Ungulata_, and of opossum-like +Marsupials. No Australian type of Marsupial has been discovered in the +Upper Eocene strata, nor any Edentate mammal. The genera (except perhaps +in the case of some of the _Insectivora, Cheiroptera_, and _Rodentia_) +are different from those of the Miocene epoch, but present a remarkable +general similarity to the Miocene and recent genera. In several cases, as +I have already shown, it has now been clearly made out that the relation +between the Eocene and Miocene forms is such that the Eocene form is the +less specialised; while its Miocene ally is more so, and the +specialisation reaches its maximum in the recent forms of the same type. + +So far as the Upper Eocene and the Miocene Mammalian Faunae are +comparable, their relations are such as in no way to oppose the +hypothesis that the older are the progenitors of the more recent forms, +while, in some cases, they distinctly favour that hypothesis. The period +in tine and the changes in physical geography represented by the +nummulitic deposits are undoubtedly very great, while the remains of +Middle Eocene and Older Eocene Mammals are comparatively few. The general +facies of the Middle Eocene Fauna, however, is quite that of the Upper. +The Older Eocene pre-nummulitic mammalian Fauna contains Bats, two genera +of _Carivora_, three genera of _Ungulata_ (probably all perissodactyle), +and a didelphid Marsupial; all these forms, except perhaps the Bat and +the Opossum, belong to genera which are not known to occur out of the +Lower Eocene formation. The _Coryphodon_ appears to have been allied to +the Miocene and later Tapirs, while _Pliolophus_, in its skull and +dentition, curiously partakes of both artiodactyle and perissodactyle +characters; the third trochanter upon its femur, and its three-toed hind +foot, however, appear definitely to fix its position in the latter +division. + +There is nothing, then, in what is known of the older Eocene mammals of +the Arctogaeal province to forbid the supposition that they stood in an +ancestral relation to those of the Calcaire Grossier and the Gypsum of +the Paris basin, and that our present fauna, therefore, is directly +derived from that which already existed in Arctogaea at the commencement +of the Tertiary period. But if we now cross the frontier between the +Cainozoic and the Mesozoic faunae, as they are preserved within the +Arctogaeal area, we meet with an astounding change, and what appears to be +a complete and unmistakable break in the line of biological continuity. + +Among the twelve or fourteen species of _Mammalia_ which are said to have +been found in the Purbecks, not one is a member of the orders +_Cheiroptera, Rodentia, Ungulata_, or _Carnivora_, which are so well +represented in the Tertiaries. No _Insectivora_ are certainly known, nor +any opossum-like Marsupials. Thus there is a vast negative difference +between the Cainozoic and the Mesozoic mammalian faunae of Europe. But +there is a still more important positive difference, inasmuch as all +these Mammalia appear to be Marsupials belonging to Australian groups, +and thus appertaining to a different distributional province from the +Eocene and Miocene marsupials, which are Austro-Columbian. So far as the +imperfect materials which exist enable a judgment to be formed, the same +law appears to have held good for all the earlier Mesozoic _Mammalia_. Of +the Stonesfield slate mammals, one, _Amphitherium_, has a definitely +Australian character; one, _Phascolotherium_, may be either Dasyurid or +Didelphine; of a third, _Stereognathus_, nothing can at present be said. +The two mammals of the Trias, also, appear to belong to Australian +groups. + +Every one is aware of the many curious points of resemblance between the +marine fauna of the European Mesozoic rocks and that which now exists in +Australia. But if there was this Australian facies about both the +terrestrial and the marine faunae of Mesozoic Europe, and if there is this +unaccountable and immense break between the fauna of Mesozoic and that of +Tertiary Europe, is it not a very obvious suggestion that, in the +Mesozoic epoch, the Australian province included Europe, and that the +Arctogaeal province was contained within other limits? The Arctogaeal +province is at present enormous, while the Australian is relatively +small. Why should not these proportions have been different during the +Mesozoic epoch? + +Thus I am led to think that by far the simplest and most rational mode of +accounting for the great change which took place in the living +inhabitants of the European area at the end of the Mesozoic epoch, is the +supposition that it arose from a vast alteration of the physical +geography of the globe; whereby an area long tenanted by Cainozoic forms +was brought into such relations with the European area that migration +from the one to the other became possible, and took place on a great +scale. + +This supposition relieves us, at once, from the difficulty in which we +were left, some time ago, by the arguments which I used to demonstrate +the necessity of the existence of all the great types of the Eocene epoch +in some antecedent period. + +It is this Mesozoic continent (which may well have lain in the +neighbourhood of what are now the shores of the North Pacific Ocean) +which I suppose to have been occupied by the Mesozoic _Monodelphia_; and +it is in this region that I conceive they must have gone through the long +series of changes by which they were specialised into the forms which we +refer to different orders. I think it very probable that what is now +South America may have received the characteristic elements of its +mammalian fauna during the Mesozoic epoch; and there can be little doubt +that the general nature of the change which took place at the end of the +Mesozoic epoch in Europe was the upheaval of the eastern and northern +regions of the Mesozoic sea-bottom into a westward extension of the +Mesozoic continent, over which the mammalian fauna, by which it was +already peopled, gradually spread. This invasion of the land was prefaced +by a previous invasion of the Cretaceous sea by modern forms of mollusca +and fish. + +It is easy to imagine how an analogous change might come about in the +existing world. There is, at present, a great difference between the +fauna of the Polynesian Islands and that of the west coast of America. +The animals which are leaving their spoils in the deposits now forming in +these localities are widely different. Hence, if a gradual shifting of +the deep sea, which at present bars migration between the easternmost of +these islands and America, took place to the westward, while the American +side of the sea-bottom was gradually upheaved, the palaeontologist of the +future would find, over the Pacific area, exactly such a change as I am +supposing to have occurred in the North-Atlantic area at the close of the +Mesozoic period. An Australian fauna would be found underlying an +American fauna, and the transition from the one to the other would be as +abrupt as that between the Chalk and lower Tertiaries; and as the +drainage-area of the newly formed extension of the American continent +gave rise to rivers and lakes, the mammals mired in their mud would +differ from those of like deposits on the Australian side, just as the +Eocene mammals differ from those of the Purbecks. + +How do similar reasonings apply to the other great change of life--that +which took place at the end of the Palaeozoic period? + +In the Triassic epoch, the distribution of the dry land and of +terrestrial vertebrate life appears to have been, generally, similar to +that which existed in the Mesozoic epoch; so that the Triassic continents +and their faunae seem to be related to the Mesozoic lands and their faunae, +just as those of the Miocene epoch are related to those of the present +day. In fact, as I have recently endeavoured to prove to the Society, +there was an Arctogaeal continent and an Arctogaeal province of +distribution in Triassic times as there is now; and the _Sauropsida_ and +_Marsupialia_ which constituted that fauna were, I doubt not, the +progenitors of the _Sauropsida_ and _Marsupialia_ of the whole Mesozoic +epoch. + +Looking at the present terrestrial fauna of Australia, it appears to me +to be very probable that it is essentially a remnant of the fauna of the +Triassic, or even of an earlier, age[7] in which case Australia must at +that time have been in continuity with the Arctogaeal continent. + +[Footnote 7: Since this Address was read, Mr. Krefft has sent us news of +the discovery in Australia of a freshwater fish of strangely Palaeozoic +aspect, and apparently a Ganoid intermediate between _Dipterus_ and +_Lepidosiren_. [The now well-known _Ceratodus_. 1894.]] + +But now comes the further inquiry, Where was the highly differentiated +Sauropsidan fauna of the Trias in Palaeozoic times? The supposition that +the Dinosaurian, Crocodilian, Dicynodontian, and to Plesiosaurian types +were suddenly created at the end of the Permian epoch may be dismissed, +without further consideration, as a monstrous and unwarranted assumption. +The supposition that all these types were rapidly differentiated out of +_Lacertilia_ in the time represented by the passage from the Palaeozoic to +the Mesozoic formation, appears to me to be hardly more credible, to say +nothing of the indications of the existence of Dinosaurian forms in the +Permian rocks which have already been obtained. + +For my part, I entertain no sort of doubt that the Reptiles, Birds, and +Mammals of the Trias are the direct descendants of Reptiles, Birds, and +Mammals which existed in the latter part of the Palaeozoic epoch, but not +in any area of the present dry land which has yet been explored by the +geologist. + +This may seem a bold assumption, but it will not appear unwarrantable to +those who reflect upon the very small extent of the earth's surface which +has hitherto exhibited the remains of the great Mammalian fauna of the +Eocene times. In this respect, the Permian land Vertebrate fauna appears +to me to be related to the Triassic much as the Eocene is to the Miocene. +Terrestrial reptiles have been found in Permian rocks only in three +localities; in some spots of France, and recently of England, and over a +more extensive area in Germany. Who can suppose that the few fossils yet +found in these regions give any sufficient representation of the Permian +fauna? + +It may be said that the Carboniferous formations demonstrate the +existence of a vast extent of dry land in the present dry-land area, and +that the supposed terrestrial Palaeozoic Vertebrate Fauna ought to have +left its remains in the Coal-measures, especially as there is now reason +to believe that much of the coal was formed by the accumulation of spores +and sporangia on dry land. But if we consider the matter more closely, I +think that this apparent objection loses its force. It is clear that, +during the Carboniferous epoch, the vast area of land which is now +covered by Coal-measures must have been undergoing a gradual depression. +The dry land thus depressed must, therefore, have existed, as such, +before the Carboniferous epoch--in other words, in Devonian times--and +its terrestrial population may never have been other than such as existed +during the Devonian, or some previous epoch, although much higher forms +may have been developed elsewhere. + +Again, let me say that I am making no gratuitous assumption of +inconceivable changes. It is clear that the enormous area of Polynesia +is, on the whole, an area over which depression has taken place to an +immense extent; consequently a great continent, or assemblage of +subcontinental masses of land must have existed at some former time, and +that at a recent period, geologically speaking, in the area of the +Pacific. But if that continent had contained Mammals, some of them must +have remained to tell the tale; and as it is well known that these +islands have no indigenous _Mammalia_, it is safe to assume that none +existed. Thus, midway between Australia and South America, each of which +possesses an abundant and diversified mammalian fauna, a mass of land, +which may have been as large as both put together, must have existed +without a mammalian inhabitant. Suppose that the shores of this great +land were fringed, as those of tropical Australia are now, with belts of +mangroves, which would extend landwards on the one side, and be buried +beneath littoral deposits on the other side, as depression went on; and +great beds of mangrove lignite might accumulate over the sinking land. +Let upheaval of the whole now take place, in such a manner as to bring +the emerging land into continuity with the South-American or Australian +continent, and, in course of time, it would be peopled by an extension of +the fauna of one of these two regions--just as I imagine the European +Permian dry land to have been peopled. + +I see nothing whatever against the supposition that distributional +provinces of terrestrial life existed in the Devonian epoch, inasmuch as +M. Barrande has proved that they existed much earlier. I am aware of no +reason for doubting that, as regards the grades of terrestrial life +contained in them, one of these may have been related to another as New +Zealand is to Australia, or as Australia is to India, at the present day. +Analogy seems to me to be rather in favour of, than against, the +supposition that while only Ganoid fishes inhabited the fresh waters of +our Devonian land, _Amphibia_ and _Reptilia_, or even higher forms, may +have existed, though we have not yet found them. The earliest +Carboniferous _Amphibia_ now known, such as _Anthracosaurus_, are so +highly specialised that I can by no means conceive that they have been +developed out of piscine forms in the interval between the Devonian and +the Carboniferous periods, considerable as that is. And I take refuge in +one of two alternatives: either they existed in our own area during the +Devonian epoch and we have simply not yet found them; or they formed part +of the population of some other distributional province of that day, and +only entered our area by migration at the end of the Devonian epoch. +Whether _Reptilia_ and _Mammalia_ existed along with them is to me, at +present, a perfectly open question, which is just as likely to receive an +affirmative as a negative answer from future inquirers. + +Let me now gather together the threads of my argumentation into the form +of a connected hypothetical view of the manner in which the distribution +of living and extinct animals has been brought about. + +I conceive that distinct provinces of the distribution of terrestrial +life have existed since the earliest period at which that life is +recorded, and possibly much earlier; and I suppose, with Mr. Darwin, that +the progress of modification of terrestrial forms is more rapid in areas +of elevation than in areas of depression. I take it to be certain that +Labyrinthodont _Amphibia_ existed in the distributional province which +included the dry land depressed during the Carboniferous epoch; and I +conceive that, in some other distributional provinces of that day, which +remained in the condition of stationary or of increasing dry land, the +various types of the terrestrial _Sauropsida_ and of the _Mammalia_ were +gradually developing. + +The Permian epoch marks the commencement of a new movement of upheaval in +our area, which dry land existed in North America, Europe, Asia, and +Africa, as it does now. Into this great new continental area the Mammals, +Birds, and Reptiles developed during the Palaeozoic epoch spread, and +formed the great Triassic Arctogaeal province. But, at the end of the +Triassic period, the movement of depression recommenced in our area, +though it was doubtless balanced by elevation elsewhere; modification and +development, checked in the one province, went on in that "elsewhere"; +and the chief forms of Mammals, Birds and Reptiles, as we know them, were +evolved and peopled the Mesozoic continent. I conceive Australia to have +become separated from the continent as early as the end of the Triassic +epoch, or not much later. The Mesozoic continent must, I conceive, have +lain to the east, about the shores of the North Pacific and Indian +Oceans; and I am inclined to believe that it continued along the eastern +side of the Pacific area to what is now the province of Austro-Columbia, +the characteristic fauna of which is probably a remnant of the population +of the latter part of this period. + +Towards the latter part of the Mesozoic period the movement of upheaval +around the shores of the Atlantic once more recommenced, and was very +probably accompanied by a depression around those of the Pacific. The +Vertebrate fauna elaborated in the Mesozoic continent moved westward and +took possession of the new lands, which gradually increased in extent up +to, and in some directions after, the Miocene epoch. + +It is in favour of this hypothesis, I think, that it is consistent with +the persistence of a general uniformity in the positions of the great +masses of land and water. From the Devonian period, or earlier, to the +present day, the four great oceans, Atlantic, Pacific, Arctic, and +Antarctic, may have occupied their present positions, and only their +coasts and channels of communication have undergone an incessant +alteration. And, finally, the hypothesis I have put before you requires +no supposition that the rate of change in organic life has been either +greater or less in ancient times than it is now; nor any assumption, +either physical or biological, which has not its justification in +analogous phenomena of existing nature. + +I have now only to discharge the last duty of my office, which is to +thank you, not only for the patient attention with which you have +listened to me so long to-day, but also for the uniform kindness with +which, for the past two years, you have rendered my endeavours to perform +the important, and often laborious, functions of your President a +pleasure instead of a burden. + + + + + +End of the Project Gutenberg EBook of Discourses, by Thomas H. 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