A second and even more interesting Royal Institution lecture dealt with the "Identity of Structure in Animals and Plants." At the present time every educated person knows that the life of animals and plants alike depends on the fact that their bodies are composed of a living material called protoplasm, a material which is identical in every important respect in both kingdoms of the living world. In the early fifties, scientific opinion was by no means clear on this matter, and certainly public opinion was most vague. Huxley discussed what was meant by organisation, and shewed that in every essential respect plants and animals alike were organised beings. Then he went on to explain the cellular theory of Schwann, which was then a novelty to a general audience. Schwann, in studying the microscopic structure of plants, noticed that their bodies were made up of little cases with firm walls; these he called cells, and declared that the whole body of the plant was composed of cells. As the walls of these cells were the most obvious and visible feature, it was supposed that they were the most essential part of the structure, and there was some difficulty in applying the cellular theory to the bodies of animals, as in most cases there are no easily visible cell-walls in animal tissues. As the result of his own observation, and from his reading of the work of others, Huxley laid down in the clearest way what is now accepted by everyone—that the presence of walls is of minor importance, and that it is the slimy contents of the cells, what is called "protoplasm," that is the important element. He declared that the protoplasm of animals was identical with the protoplasm of plants, and that plants were "animals confined in wooden cases." He agreed with Schwann that the cell, using the term to imply the contents rather than the wall, was of fundamental importance, and was the unit of structure of the whole world of life. On the other hand, he declared that it could not be looked at as the unit of function: he denied that the powers and properties of a living body were simply the sum of the powers and properties of the single cells. In this opinion he was not followed by physiologists until quite recently. For many years physiologists held that cells were units of function just as much as they are units of structure; but in the last ten years there has been a strong return to the opinion of Huxley.

In 1851 two very important memoirs were published in the Transactions of the Royal Society, which contained the results of Huxley's observations of the interesting animals known as "tunicates." The first of these papers begins as follows:

"The Salpae, those strange gelatinous animals, through masses of which the voyager in the great ocean sometimes sails day after day, have been the subject of a great controversy since the time of the publication of the celebrated work of Chamisso, De Animalibus Quibusdam e Classe Vermium Linnaeana. In this work there were set forth, for the first time, the singular phenomena presented by the reproductive processes of these animals,—phenomena so strange, and so utterly unlike anything then known to occur in the whole province of zooelogy, that Chamisso's admirably clear and truthful account was received with almost as much distrust as if he had announced the existence of a veritable Peter Schlemihl."

According to Chamisso, salps appeared in two forms: solitary forms, and forms in which a number of salps are united into a long chain. Each salp of the aggregate form contains within it an embryo receiving nutrition from the mother by a connection similar to the placenta by which the embryo of a mammal receives nourishment from the blood of the mother. These embryos grow up into the solitary form, and the solitary form gives rise to a long chain of the aggregate form which developes in the interior of the body. Chamisso compared this progress to the development of insects. "Supposing," he said, "caterpillars did not bodily change into butterflies, but by a process of sexual breeding produced young which grew into the ordinary adults, and that these adults, as indeed they do, gave rise to caterpillars by sexual reproduction, then there would be a true alternation of generations." The first generation would give rise to a second generation totally unlike itself, and this second generation would reproduce, not its kind, but the first generation; such an alternation of generations he stated to occur among the salps. Huxley had an excellent opportunity to study this question at Cape York in November, 1849. "For a time the sea was absolutely crowded with Salpae, in all stages of growth, and of size very convenient for examination." He was able to verify the general truth of Chamisso's statement. The aggregate form of Salpa always gives rise to the solitary salps, and the solitary salps always give rise to chains of the aggregate salps. But the process of reproduction he shewed to be quite different in the two cases. The solitary salp produces in its interior a little stolon or diverticulum which contains an outgrowth from the circulatory system, and this stolon gradually becomes pinched off into the members of the chain of the aggregate form. The salps of the aggregate form are therefore merely buds from the solitary form, and are not produced in the ordinary way, by sexual generation. On the other hand, each salp of the chain has within it a true egg-cell. This is fertilised by a male cell, and within the body of the parent, nourished by the blood of the parent, grows up into the solitary form. There is then an alternation of generations, but there are not two sexual generations. The sexual generation of chain salps gives rise to forms which reproduce by buds. From this conclusion, with which all later observers have agreed, Huxley went on to his theory of individuality. Different names had been given to the two forms, but Huxley declared that neither form was a true zooelogical individual; they were only parts of individuals or organs, and the true individual was the complete cycle involving both forms.

In addition to determining the interesting method of reproduction, Huxley made an elaborate investigation of the structure of Salpa. On one occasion only the Rattlesnake came across a quantity of an allied Ascidian, Pyrosoma, which had received its name from its phosphorescence.

"The sky was clear but moonless, and the sea calm; and a more beautiful sight can hardly be imagined than that presented from the deck of the ship as she drifted, hour after hour, through this shoal of miniature pillars of fire gleaming out of the dark sea, with an ever-waning, ever brightening, soft bluish light, as far as the eye could reach on every side. The Pyrosomata floated deep, and it was only with difficulty that some were procured for examination and placed in a bucketful of sea-water. The phosphorescence was intermittent, periods of darkness alternating with periods of brilliancy. The light commenced in one spot, apparently on the surface of one of the zooeids, and gradually spread from this as a centre in all directions; then the whole was lighted up: it remained brilliant for a few seconds, and then gradually faded and died away, until the whole mass was dark again. Friction at any point induces the light at that point, and from thence the phosphorescence spreads over the whole, while the creature is quite freshly taken; afterwards, the illumination arising from friction is only local."

Dealing with these creatures in the broad anatomical spirit with which he had studied the Medusae, Huxley shewed the typical structure manifested in the different forms, and that was common to them and the Ascidians or sea-squirts of the seashore. In a second paper on "Appendicularia and Doliolum" he made further contributions to our knowledge of these interesting creatures. Appendicularia is a curious little Ascidian, differing from all the others in its possession of a tail. Earlier observers had obtained it on various parts of the ocean surface, but had failed entirely to detect its relationship to the ordinary Ascidians. Chamisso got it near Behring's Straits and thought that it was more nearly allied to "Venus's Girdle," a Coelenterate. Mertens, another distinguished zooelogist, had declared that "the relation of this animal with the Pteropods (a peculiar group of molluscs) is unmistakable"; while Mueller, a prince among German anatomists, confessed that "he did not know in what division of the animal kingdom to place this creature." Huxley shewed that it possessed all the characteristic features of the Ascidians, the same arrangement of organs, the same kind of nervous system, a respiratory chamber formed from the fore part of the alimentary canal, and a peculiar organ running along the pharynx which Huxley called the endostyle and which is one of the most striking peculiarities of the whole group. The real nature of the tail was Huxley's most striking discovery. He pointed out that ordinary Ascidians begin life as tiny tadpole-like creatures which swim freely by the aid of a long caudal appendage; and that while these better-known Ascidians lose their tails when they settle down into adult life, the Appendiculariae are Ascidians which retain this larval structure throughout life. Von Baer had shown that in the great natural groups of higher animals some forms occur which typify, in their adult condition, the larval state of the higher forms of the group. Thus, among the amphibia, frogs have tails in the larval or tadpole condition; but newts throughout life remain in the larval or tailed condition. Appendicularia he considered to be the lowest form of the Ascidians, and to typify in its adult condition the larval stages of the higher Ascidians.

By this remarkable investigation of the structure of the group of Ascidians, and display of the various grades of organisation, Huxley paved the way for one of the great modern advances in knowledge. When, later on, the idea of evolution was accepted, and zooelogists began hunting out the pedigree of the back-boned animals, it was discovered that Ascidians were modern representatives of an important stage in the ancestry of vertebrate animals, and, therefore, of man himself. There are few more interesting chapters in genealogical zooelogy than those which reveal the relationship between Amphioxus and fish on the one hand, and Ascidians on the other; for fish are vertebrates, and Ascidians, on the old view, are lowly invertebrates. The details of these relationships have been made known to us by the brilliant investigations of several Germans, by Kowalevsky, a Russian, by the Englishmen Ray Lankester and Willey, and by several Americans and Frenchmen. But behind the work of all these lies the pioneer work of Huxley, who first gathered the group of Ascidians together, and in a series of masterly investigations described its typical structure.

Huxley's next great piece of work was embodied in a memoir published in the Transactions of the Royal Society in 1853, and which remains to the present day a model of luminous description and far-reaching ideas. It was a treatise on the structure of the great group of molluscs, and displays in a striking fashion his method of handling anatomical facts, and deducing from them the great underlying principles of construction. The shell-fish with which he dealt specially were those distinguished as cephalous, because, unlike creatures such as the oyster and mussel, they had something readily comparable with the head of vertebrates. He began by pointing out what problems he hoped to solve. The anatomy of many of the cephalous molluscs was known, but the relation of structures present in one to structures present in another group had not been settled.

"It is not settled whether the back of a cuttle-fish answers to the dorsal or ventral surface of a gasteropod. It is not decided whether the arms and funnels of the one have or have not their homologues in the other. The dorsal integument of a Doris and the cloak of a whelk are both called 'mantle,' without any evidence to show that they are really homologous. Nor do very much more definite notions seem to have prevailed with regard to the archetypal molluscous form, and the mode in which (if such an archetype exist) it becomes modified in the different secondary types."

He had taken from the surface of the sea a number of transparent shell-fish, and had been able to study the structure and arrangement of their organs "by simple inspection, without so much as disturbing a single beat of their hearts." From knowledge gained in this fashion, and from ordinary dissection of a number of common snails, cephalopods, and pteropods, he was able to describe in a very complete way the anatomical structure of cephalous molluscs. The next natural step, he stated, would have been to describe the embryonic development of the organs of these different creatures in order that a true knowledge might be gained of what were the homologous or really corresponding parts in each. Having had no opportunity to make such embryological studies for himself, he fell back on numerous accounts of development by Koelliker, Van Beneden, Gegenbauer, and others, and so gradually arrived at a conception of what he called the "archetype" of the cephalous molluscs. As the word archetype was borrowed from old metaphysical ideas dating back to the time of Plato, he took care to state that what he meant by it was no more than a form embodying all that could be affirmed equally respecting every single kind of cephalous mollusc, and by no means an "idea" upon which it could be supposed that animal forms had been modelled. He described this archetype, and showed the condition of the different systems of organs which it could be supposed to possess, and how these organs were modified in the different existing groups. This archetypal mollusc of Huxley's was a creature with a bilaterally symmetrical head and body. On the ventral side of the body it possessed a peculiar locomotor appendage, the so-called foot, and the dorsal surface of the body secreted a shell. Its nervous system consisted of three pairs of ganglia or brains, one pair in the head, one in the foot, and a third in the viscera. He shewed how the widely different groups of cephalous molluscs could be conceived as modifications of this structure, and extended the conception so as to cover all other molluscs.

Quite apart from the anatomical value of this paper, and although all technical details have been omitted here, it is necessary to say that merely as a series of intricate anatomical descriptions and comparisons, this memoir was one of the most valuable of any that Huxley wrote. The working out of the theory of the archetype is peculiarly interesting to compare with modern conceptions. To those of us who began biological work after the idea of evolution had been impressed upon anatomical work, it is very difficult to follow Huxley's papers without reading into them evolutionary ideas. In the article upon Mollusca, written for the ninth edition of the Encyclopaedia Britannica, by Professor Ray Lankester, the same device of an archetypal or, as Lankester calls it, a schematic mollusc, is employed in order to explain the relations of the different structures found in different groups of molluscs to one another. Lankester's schematic mollusc differs from Huxley's archetypal mollusc only as a finished modern piece of mechanism, the final result of years of experiment, differs from the original invention. The method of comparing the schematic mollusc with the different divergent forms in different groups is identical, and yet, while the ideas of Darwin are accepted in every line of Lankester's work, Huxley was writing six years before the publication of The Origin of Species. There was growing up in Huxley's mind, partly from his own attempts to arrange the anatomical facts he discovered in an intelligible series, the idea that within a group the divergencies of structure to be found had come about by the modification of an original type. Not only did he conceive of such an evolution as the only possible explanation of the facts, but he definitely used the word evolution to convey his ideas. On the other hand, he was firmly convinced that such evolution was confined within the great groups. For each group there was a typical structure, and modifications by defect or excess of the parts of the definite archetype gave rise to the different members of the group. Moreover, he confined this evolution in the strictest possible way to each group; he did not believe that what was called anamorphosis—the transition of a lower type into a higher type—ever occurred. To use his own words:

"If, however, all Cephalous Mollusca, i.e., all Cephalopoda, Gasteropoda, and Lamellibranchiata, be only modifications by excess or defect of the parts of a definite archetype, then, I think, it follows as a necessary consequence, that no anamorphosis takes place in this group. There is no progression from a lower to a higher type, but merely a more or less complete evolution of one type. It may indeed be a matter of very grave consideration whether true anamorphosis ever occurs in the whole animal kingdom. If it do, then the doctrine that every natural group is organised after a definite archetype, a doctrine which seems to me as important for zooelogy as the theory of definite proportions for chemistry, must be given up."

It is of great historical interest to notice how closely actual consideration of the facts of the animal kingdom took zooelogists to an idea of evolution, and yet how far they were from it as we hold it now. It is fashionable at the present time to attempt to depreciate the immense change introduced by Darwin into zooelogical speculation, and the method employed is largely partial quotation, or reference to the kind of ideas found in papers such as this memoir by Huxley. The comparison between the types of the great groups and the combining proportions of the chemical elements shows clearly that Huxley regarded the structural plans of the great groups as properties necessary and inherent in these groups, just as the property of a chemical element to combine with another chemical substance only in a fixed proportion is necessary and inherent in the existing conception of it. There was no glimmer of the idea that these types were not inherent, but merely historical results of a long and slow series of changes produced by the interaction of the varied conditions of life and the intrinsic qualities of living material.

In two lectures delivered at the Royal Institution in 1854 and 1855, the one on "The Common Plan of Animal Forms," the other on "The Zooelogical Arguments Adduced in Favour of the Progressive Development of Animal Life in Time," show, so far as the published abstracts go, the same condition of mind. The idea of progressive development of all life from common forms was not unknown to Huxley and his contemporaries, but was rejected by them. In the first of these two lectures he took four great groups of animals, the Vertebrates, the Articulata, the Mollusca, and the Radiata, and explained what was the archetype of each. He shewed the distinctiveness of each plan of structure, and then discussed the relations of the ideas suggested by Von Baer to these archetypes. He stated explicitly that while the adult forms were quite unlike one another, there were traces of a common plan to be derived from a study of their embryonic development. Such a trace of a common plan he had himself suggested when he compared the foundation-membranes of the Medusae with the first foundation-membranes of vertebrate embryos. This was going a long way towards modern ideas; but he stopped short, and gave no hint that he believed in the possibility of the development of one plan from a lower or simpler plan. The second lecture dealt with the kind of ideas which were crystallised in the popular but striking work of Chambers, entitled Vestiges of Creation. Chambers attacked the theological view that all animals and plants had been created at the beginning of the world, and maintained that geological evidence showed the occurrence of a progressive development of animal life. Huxley, like all zooelogists and geologists who knew anything of the occurrence of fossils in the rocks of past ages, agreed with the general truth of the conception that a progressive development had occurred which showed that the species now existing were represented in the oldest rocks by species now extinct. But the examples he brought forward were all limited to evolution within the great groups, and did not affect his idea that archetypes were fixed and did not pass into each other. Moreover, he summed up strongly against the suggestion that there was any parallel between the succession of life in the past and the forms assumed by modern animals in their embryological development. So far as the present writer is able to judge from study of the literature of this period, the possibility of evolution was present in an active form in the minds of Huxley and of his contemporaries, and in an extraordinary way they brought together evidence which afterwards became of firstrate importance; but the idea in its modern sense was rejected by them.

In 1854 Huxley's uncomfortable period of probation came to an end. Edward Forbes, who held the posts of Palaeontologist to the Geological Survey, and Lecturer on General Natural History at the Metropolitan School of Science Applied to Mining and the Arts, vacated these on his appointment to the Chair of Natural History in the University of Edinburgh, and Sir H. De La Beche, the then Director-General of the Geological Survey, offered both the posts to Huxley—who in June and July of that year had given lectures at the school in place of Forbes. Huxley says himself:

"I refused the former point-blank, and accepted the latter only provisionally, telling Sir Henry that I did not care for fossils, and that I should give up natural history as soon as I could get a physiological post. But I held the office for thirty-one years, and a large part of my work has been palaeontological."

The salary of the post of Lecturer on Natural History was scanty, but De La Beche, who evidently recognised Huxley's genius, and was anxious to have him attached even against his will to palaeontological work, created a place for him as Naturalist to the Geological Survey, by which a more suitable income was found for him. His official duties were at first in the Geological Museum of the Survey, but were distinguished from those of the special Palaeontologist, Mr. Harvey. His income was now assured, and for the rest of his life, until towards its close, when he retired to Eastbourne, he lived the ordinary life of a professional man of science in London. He was now able to marry, and on July 21, 1855, he was married to a lady whom he had met in Sydney in 1847, and whom he had not seen since the Rattlesnake left Sydney finally in the beginning of May, 1850.

During the years 1856, 1857, and 1858, he held the post of Fullerian Professor of Physiology in the Royal Institution, choosing as the title of his first two courses of lectures Physiology and Comparative Anatomy, as he still cherished the idea of being in the first place a physiologist.



"Moreover," writes Professor Michael Foster, "like most other young professional men of science, he had to eke out his not too ample income by labours undertaken chiefly for their pecuniary reward. He acted as examiner, conducting for instance, during the years 1856 to 1863, and again 1865 to 1870, the examinations in physiology and comparative anatomy at the University of London, making even an examination paper feel the influence of the new spirit in biology; and among his examinees at that time there was at least one who, knowing Huxley's writings, but his writings only, looked forward to the viva voce test, not as a trial but as an occasion of delight. He wrote almost incessantly for all editors who were prepared to give adequate pay to a pen able to deal with scientific themes in a manner at once exact and popular, incisive and correct. During this period he was gradually passing from his first anatomical love, the structure of the Invertebrates, to Vertebrate work, and although he continued to take a deep interest in the course of the progress of research in that group of animals, the publication of his great work on oceanic hydrozoa by the Ray Society was the last piece of important work he wrote upon any anatomical subject apart from vertebrates. His work in connection with the Geological Survey naturally attracted his attention most closely to vertebrates, and, towards the close of the fifties, he was led to make a special study of vertebrate embryology, a subject which the investigations of Koelliker and others in Germany were bringing into prominence. The first result of this new direction of his enquiries was embodied in a Croonian Lecture delivered in 1858 'On the Theory of the Vertebrate Skull.' Sir Richard Owen, who was at that time the leading vertebrate anatomist in England, had given his support to an extremely complicated view of the skull as being formed of a series of expanded vertebrae moulded together. The theory was really a legacy from an old German school of which the chief members were Goethe, the poet, and Oken, a naturalist, who was more of a metaphysical philosopher than of a morphologist. Huxley pointed out the futility of attempting to regard the skull as a series of segments, and of supporting this view by trusting to superficial resemblances and abstract reasoning, when there was a definite method by which the actual building up of the skull might be followed. Following the lines laid down by Rathke, another of the great Germans from whose investigations he was always so willing to find corroboration and assistance in his own labours, he traced the actual development of the skull in the individual. He shewed that the foundations of the skull and of the backbone were laid down in a fashion quite different, and that it was impossible to regard both skull and backbone as modifications of a common type laid down right along the axis of the body. The spinal column and the skull start from the same primitive condition, whence they immediately begin to diverge. It may be true to say that there is a primitive identity of structure between the spinal or vertebral column and the skull; but it is no more true that the adult skull is a modified vertebral column than it would be to affirm that the vertebral column is a modified skull."

Since this famous lecture, a number of distinguished anatomists have studied the development of the skull more fully; but they have not departed from the methods of investigation laid down by Huxley, and their conclusions have differed only in greater elaboration of detail from the broad lines laid down by him. Apart from its direct scientific value, this lecture was of importance as marking the place to which Huxley had attained in the scientific world. Two years later, it is true, the London Times, referring to a famous debate at a meeting of the British Association at Oxford, spoke of him as "a Mr. Huxley"; but in the scientific world he was accepted as the leader of the younger anatomists, and as one at least capable of rivalling Owen, who was then at the height of his fame. The Croonian Lecture was in a sense a deliberate challenge to Owen, and in these days before Darwin, to challenge Owen was to claim equality with the greatest name in anatomical science.



CHAPTER V

CREATURES OF THE PAST

Beginning Palaeontological Work—Fossil Amphibia and Reptilia—Ancestry of Birds—Ancestry of the Horse—Imperfect European Series Completed by Marsh's American Fossils—Meaning of Geological Contemporaneity—Uniformitarianism and Catastrophism Compared with Evolution in Geology—Age of the Earth—Intermediate and Linear Types.

Although Huxley took a post connected with Geology only because it was the most convenient opening for him, it was not long before he became deeply interested not only in the fossils, which at first he despised, but in the general problems of geology. He began by co-operation with Mr. Salter in the determination of fossils for the Geological Survey. The mere work of defining genera and species and naming and describing new species appealed very little to him. He had none of the collector's passion for new species; his interest in a creature being not whether or no it was new to science, but what general problems of biology its structure helped to elucidate. While he assisted in the routine work of determining the zooelogical position of the fossils sent in to the museum by the Survey, he carried investigations much farther than the duties of the post required when interesting zooelogical problems arose. His earliest notes were written in association with his colleague, and consisted of technical descriptions of some small fossils from the Downton Sandstones which were supposed to be fish-shields. The peculiarities of structure presented by these aroused his interest, and he began an elaborate series of investigations upon palaeozoic fishes in general. Earlier zooelogists, such as the great Agassiz, had devoted most of their attention to careful and exact description of the different fossil fishes with which they became acquainted. Huxley at once began to investigate the relations that existed among the different kinds of structure exhibited in the different fish. He laid down the lines upon which future work has been conducted, and, precisely as he did in the case of molluscs, he started future investigators upon lines of research the ends of which have not yet been reached. His work upon Devonian Fishes, published in 1861, threw an entirely new light upon the affinities of these creatures, and still remains a standard work.

He made a similar, although less important, series of investigations upon some of the great extinct Crustacea; but, perhaps, his most important palaeontological work was done later, after he had been convinced by Darwin of the fact of evolution. In 1855 he had expressed the opinion that the study of fossils was hopeless if one sought in it confirmation of the doctrine of evolution; but five-and-twenty years' continuous work completely reversed his opinion, and in 1881, addressing the British Association at York he declared that "if zooelogists and embryologists had not put forward the theory, it would have been necessary for palaeontologists to invent it." In three special groups of animals his study of fossils enabled him to assist in bridging over the gaps between surviving groups of creatures by study of creatures long extinct. He began to study the structure of the Labyrinthodonts, a group of extinct monsters which received their name from the peculiar structure of their teeth. He published elaborate descriptions of Anthracosaurus from the coal-measures of Northumberland, of Loxomma from the lower carboniferous of Scotland, and of several small forms from the coal-measures of Kilkenny, in Ireland, as well as describing skulls from Africa and a number of fragmentary bones from different localities. But in all this work it was the morphology of the creatures that interested him, and the light which their structure threw upon the structure of each other and of their nearest allies. He shewed that these monsters stood on the borderland between fishes, amphibia, and reptiles, and he added much to our knowledge of the true structure of these great groups. Next, he turned to the extinct reptiles of the Mesozoic age. It was generally believed that the Pterodactyls, or flying reptiles, were the nearest allies of birds, but Huxley insisted that the resemblances between the wings were simply such superficial resemblances as necessarily exist in organs adapted to the same purpose. About the same time, Cope in America, and Phillips and Huxley, in England, from study of the bones of the Dinosaurs, another great group of extinct reptiles, declared that these were the nearest in structure to birds. In association with the upright posture, the ilium or great haunch-bone of birds extends far forwards in front of the articulation of the thigh-bone, so that the pelvis in this region has a T-shape, the ilium forming the cross-bar of the T, and the femur or thigh-bone the downward limb. Huxley shewed that a large number of the Dinosaurs had this and other peculiarities of the bird's pelvis, and separated these into a group which he called the "Ornithoscelida," seeing in them the closest representatives of the probable reptilian ancestors of birds. While further work and the discovery of a still greater number of extinct reptiles has made it less probable that these were the actual ancestors of birds, Huxley's work in this, as in the many other cases we have shown, proved not only of great value in itself, but led to a continually increasing series of investigations by others. It is not always the pioneer that makes the greatest discoveries in a new country, but the work of the pioneer makes possible and easier the more assured discoveries of his followers.

A third great piece of palaeontological investigation with which the name of Huxley will always be associated, is the most familiar of all the instances taken from fossils in support of the evolution of animals. This famous case is the pedigree of the horse. In 1870, in an address delivered to the Geological Society of London, Huxley had shewn that there was a series of animals leading backwards from the modern horse to a more generalised creature called Anchitherium, and found in the rocks of the Miocene period. He suggested that there were, no doubt, similar fossils leading still further backwards towards the common mammalian type of animal, with five fingers and five toes, and went the length of suggesting one or two fossils which might stand in the direct line of ancestry. But in 1876 he visited America, and had the opportunity of consulting the marvellous series of fossils which Professor Marsh had collected from American Tertiary beds. Professor Marsh allowed him the freest use of his materials and of his conclusions, and the credit of the final result is to be shared at least equally between Marsh and Huxley. The final result was a demonstrative proof of the possible course of evolution of the horse, given in a lecture delivered by Huxley in New York on Sept. 22, 1876, and illustrated by drawings from specimens in Marsh's collection. The matter of the lecture has become so important a part of all descriptive writing on evolution, and the treatment is so characteristic of Huxley's brilliant exposition, that it is worth while to make some rather long quotations from it. The lecture was published in the New York papers, and afterwards with other matter formed a volume of American Addresses, published by Macmillan, in London.

"In most quadrupeds, as in ourselves, the forearm contains distinct bones called the radius and the ulna. The corresponding region in the horse seems at first to possess but one bone. Careful observation, however, enables us to distinguish in this bone a part which clearly answers to the upper end of the ulna. This is closely united with the chief mass of the bone which represents the radius, and runs out into a slender shaft which may be traced for some distance downwards on the back of the radius, and then in most cases thins out and vanishes. It takes still more trouble to make sure of what is nevertheless the fact, that a small part of the lower end of the bone of the horse's forearm, which is only distinct in a very young foal, is really the lower extremity of the ulna.

"What is commonly called the knee of a horse is its wrist. The 'cannon bone' answers to the middle bone of the five metacarpal bones which support the palm of the hand in ourselves. The 'pastern,' 'coronary,' and 'coffin' bones of veterinarians answer to the joints of our middle fingers, while the hoof is simply a greatly enlarged and thickened nail. But, if what lies below the horse's 'knee' thus corresponds to the middle finger in ourselves, what has become of the four other fingers or digits? We find in the places of the second and fourth digits only two slender splint-like bones, about two-thirds as long as the cannon bone, which gradually taper to their lower ends and bear no finger joints, or, as they are termed, phalanges. Sometimes small bony or gristly nodules are to be found at the bases of these two metacarpal splints, and it is probable that these represent rudiments of the first and fifth digits. Thus the part of the horse's skeleton which corresponds with that of the human hand contains one overgrown middle digit, and at least two imperfect lateral digits; and these answer, respectively, to the third, the second, and the fourth digits in man.

"Corresponding modifications are found in the hind limb. In ourselves, and in most quadrupeds, the leg contains two distinct bones, a large bone, the tibia, and a smaller and more slender bone, the fibula. But, in the horse, the fibula seems, at first, to be reduced to its upper end; a short slender bone united with the tibia and ending in a point below occupying its place. Examination of the lower end of a young foal's shin-bone, however, shews a distinct portion of osseous matter, which is the lower end of the fibula; so that the apparently single lower end of the shin-bone is really made up of the coalesced ends of the tibia and fibula, just as the apparently single lower end of the fore-arm bone is composed of the coalesced radius and ulna.

"The heel of the horse is the part commonly known as the hock; the hinder cannon bone answers to the middle metatarsal bone of the human foot, the pastern, coronary, and coffin bones, to the middle-toe bones; the hind hoof to the nail, as in the fore foot. And, as in the fore foot, there are merely two splints to represent the second and fourth toes. Sometimes a rudiment of a fifth toe appears to be traceable."

Having in the same fashion described the highly complicated and peculiar structure of the teeth of modern horses, Huxley proceeded:

"To anyone who is acquainted with the morphology of vertebrated animals, these characteristic structures of the horse show that it deviates widely from the general structure of mammals; and that the horse type is, in many respects, an extreme modification of the general mammalian plan. The least modified mammals, in fact, have the radius and ulna, the tibia and fibula, distinct and separate. They have five distinct and complete digits on each foot, and no one of these digits is very much larger than the rest. Moreover, in the least modified mammals, the total number of the teeth is very generally forty-four, while in the horse the usual number is forty, and, in the absence of the canines, it may be reduced to thirty-six; the incisor teeth are devoid of the fold seen in those of the horse; the grinders regularly diminish in size from the middle of the series to its front end; while their crowns are short, early attain their full length, and exhibit simple ridges or tubercles, in place of the complex foldings of the horse's grinders.

"Hence the general principles of the hypothesis of evolution lead to the conclusion that the horse must have been derived from some quadruped which possessed five complete digits on each foot; which had the bones of the forearm and of the leg complete and separate; and which possessed forty-four teeth, among which the crown of the incisors and grinders had a simple structure; while the latter gradually increased in size from before backwards, at any rate in the anterior part of the series, and had short crowns.

"And if the horse had been thus evolved, and the remains of the different stages of its evolution have been preserved, they ought to present us with a series of forms in which the number of the digits becomes reduced; the bones of the forearm and leg gradually take on the equine condition; and the form and arrangement of the teeth successively approximate to those which obtain in existing horses.

"Let us turn to the facts and see how far they fulfill these requirements of the doctrine of evolution.

"In Europe abundant remains of horses are found in the Quaternary and later Tertiary strata as far as the Pliocene formation. But these horses, which are so common in the cave-deposits and in the gravel of Europe, are in all essential respects like existing horses, and that is true of all the horses of the later part of the Pliocene epoch. But, in the deposits which belong to the earlier Pliocene, and later Miocene epochs, and which occur in Britain, in France, in Germany, in Greece, in India, we find animals which are extremely like horses—which in fact are so similar to horses, that you may follow descriptions given in works upon the anatomy of the horse, upon the skeletons of these animals—but which differ in some important particulars. For example, the structure of their fore and hind limbs is somewhat different. The bones, which, in the horse are represented by two long splints, imperfect below, are as long as the middle metacarpal and metatarsal bones; and, attached to the extremity of each, is a digit with three joints of the same general character as those of the middle digit, only very much smaller. These small digits are so disposed that they could have had but very little functional importance, and they must have been rather of the nature of the dew-claws, such as are to be found in many ruminant animals. The Hipparion, as the extinct European three-toed horse is called, in fact presents a foot similar to that of the American Protohippus except that in Hipparion the smaller digits are situated further back, and are of smaller proportional size than in the Protohippus.

"The ulna is slightly more distinct than in the horse; and the whole length of it, as a very slender shaft, intimately united with the radius, is completely traceable. The fibula appears to be in the same condition as in the horse. The teeth of the Hipparion are essentially similar to those of the horse, but the pattern of the grinders is in some respects a little more complex, and there is a depression on the face of the skull in front of the orbit, which is not seen in existing horses.

"In the earlier Miocene and perhaps in the Eocene deposits of some parts of Europe, another distinct animal has been discovered, which Cuvier, who first described some fragments of it, considered to be a Palaeotherium, but as further discoveries threw new light on its structure, it was recognised as a distinct genus, under the name of Anchitherium.

"In its general characters the skeleton of Anchitherium is very similar to that of the horse, in fact Lartet and De Blainville called it Palaeotherium equinum or Hippoides; and De Cristol, in 1847, said that it differed from Hipparion in little more than the characters of the teeth, and gave it the name of Hipparitherium. Each foot possesses three complete toes: while the lateral toes are much larger in proportion to the middle toe than in Hipparion, and doubtless rested on the ground in ordinary locomotion. The ulna is complete and quite distinct from the radius, although firmly united with the latter. The fibula seems also to have been complete; its lower end, though intimately united with that of the tibia, is clearly united with that of the latter bone. There are forty-four teeth; the incisors have no strong pit. The canines seem to have been well developed in both sexes. The first of the seven grinders, which, as I have said, is frequently absent, and, when it does exist, is small in the horse, is a good-sized and permanent tooth, while the grinder which follows it is but little larger than the hinder ones. The crowns of the grinders are short, and, although the fundamental pattern of the horse-tooth is discernible, the front and back ridges are less curved, the accessory pillars are wanting, and the valleys, much shallower, are not filled up with cement."

Then, after describing his early efforts to trace the descent of the horse from European fossils, Huxley goes on to relate the new light thrown on the matter from the American discoveries of Professor Marsh:

"You are all aware that, when your country was first discovered by Europeans, there were no traces of the existence of the horse in any part of the American continent. The accounts of the conquest of Mexico dwell on the astonishment of the natives of that country when they first became acquainted with that astounding phenomenon, a man seated upon a horse. Nevertheless, the investigations of American geologists have proved that the remains of horses occur in the most superficial deposits of both North and South America, just as they do in Europe. Therefore, for some reason or other,—no feasible suggestion on that subject, so far as I know, has been made,—the horse must have died out on this continent at some period preceding the discovery of America. Of late years there has been discovered in your Western territories that marvellous accumulation of deposits, admirably adapted for the preservation of organic remains, to which I referred the other evening, and which furnishes us with a consecutive series of records of the fauna of the older half of the Tertiary epoch, for which we have no parallel in Europe. The researches of Leidy and others have shewn that forms allied to the Hipparion and the Anchitherium are to be found among these remains. Rut it is only recently that the admirably conceived and most thoroughly and patiently worked-out investigations of Professor Marsh have given us a just idea of the vast fossil wealth and of the scientific importance of these deposits. I have had the advantage of glancing over the collections in Yale Museum; and I can truly say that, so far as my knowledge extends, there is no collection from any one region and series of strata comparable, for extent, or for care with which the remains have been got together, or for their scientific importance, to the series of fossils which he has deposited there. This vast collection has yielded evidence bearing on the question of the pedigree of the horse of the most striking character. It tends to show that we must look to America rather than to Europe for the original seat of the equine series; and that the archaic forms and successive modifications of the horse's ancestry are far better preserved here than in Europe.

"Professor Marsh's kindness has enabled me to put before you a diagram, every figure of which is an actual representation of some specimen which is to be seen at Yale at this present time.

"The succession of forms which he has brought together carries us from the top to the bottom of the Tertiaries. Firstly, there is the true horse. Next we have the American Pliocene form of the horse (Pliohippus): in the conformation of its limbs it presents some very slight deviations from the ordinary horse, and the crowns of the grinding teeth are shorter. Then comes the Protohippus, which represents the European Hipparion, having one large digit and two small ones on each foot, and the general characters of the forearm and leg to which I have referred. But it is more valuable than the European Hipparion for the reason that it is devoid of some of the peculiarities of that form—peculiarities which tend to show that the European Hipparion is rather a member of a collateral branch than a form in the direct line of succession. Next, in the backward order in time, is the Miohippus, which corresponds pretty nearly with the Anchitherium of Europe. It presents three complete toes—one large median and two smaller lateral ones: and there is a rudiment of that digit which answers to the little finger of the human race.

"The European pedigree of the horse stops here; in the America Tertiaries, on the contrary, the series of ancestral equine forms is continued into the Eocene formations. An older Miocene form, called Mesohippus, has three toes in front, with a large splint-like rudiment representing the little finger; and three toes behind. The radius and ulna, the tibia and fibula, are distinct, and the short crowned molar teeth are Anchitherioid in pattern.

"But the most important discovery of all is the Orohippus which comes from the Eocene formation, and is the oldest member of the equine series yet known. Here we find four complete toes on the front limb, three toes on the hind limb, a well-developed ulna, a well-developed fibula, and short-crowned grinders of a simple pattern.

"Thus, thanks to these important researches, it has become evident that, so far as our present knowledge extends, the history of the horse type is exactly and precisely that which could have been predicted from a knowledge of the principles of evolution; and the knowledge we now possess justifies us completely in the anticipation that, when the still lower Eocene deposits, and those which belong to the Cretaceous period have yielded up their remains of ancestral equine animals, we shall find, first, a form with four complete toes and a rudiment of the innermost or first digit in front, with probably a rudiment of the fifth digit in the hind foot; while, in the older forms, the series of digits will be more and more complete until we come to the five-toed animals, in which, if the doctrine of evolution is well founded, the whole series must have taken its origin."

Just as Huxley was successful, when only the ancestry to Miocene times was known, in predicting the discovery of older forms in the older Miocene and upper Eocene, so his prediction of older Eocene forms carrying the chain back to five-toed creatures proved correct. One of the new links was indeed discovered before his lecture had passed through the press, and he was able to add in a footnote some details of the structure of the four-toed Eohippus from the lower Eocene beds. Further discoveries have connected these with the five-toed ancestors of the Tapirs, and there is the strongest reason to suppose that we now know as nearly as possible the line of ancestry of the horse back to the primitive forms common to all the higher mammals. It would, of course, be beyond possibility of proof that the exact fossils described were the actual ancestors of the horse; but that they are exceedingly close allies of these, and that among them some actual ancestors exist cannot reasonably be doubted.

Although he had embarked upon geological work with some distaste, Huxley became very closely associated with it as years went on, and indeed, about the seventies, had abandoned his intention to devote himself specially to physiology, and declared himself to be in the first place a palaeontologist. In 1876 he had accomplished so much that the Geological Society gave him its chief distinction, awarding him the Wollaston Medal in recognition of his services to geological science. He acted as Secretary to the Geological Society from 1859 to 1862, and he was President from 1868 to 1870. In 1862, the President being incapacitated, Huxley delivered as Deputy-President the Presidential Address. This address is famous in the history of geology, because for the first time it stated clearly and in permanent form a doctrine now taken as a first principle in all geological text-books. A large part of geology is the attempt to read the past history of the earth from the evidence given by the successive strata of rocks that form its crust.

"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."

It is of the utmost importance to determine whether or no the same series occurring vertically in the same order in different parts of the earth were deposited at the same time. To explain the problem, Huxley took the following concrete example:

"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 at the same time, he says, 'No, only within the same great epoch.' And if, in pursuing the enquiry, 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.'"

Most of the standard writers on palaeontology had assumed that the presence in two beds at different parts of the world of the same fossils implied that the beds were contemporaneous, that they had been formed at the same time. Huxley pointed out that the fact of identical fossils being present was, on the whole, evidence against the beds having been formed at the same time. Even some of the older writers who believed in species having been created at definite places at definite times had seen that time must have been required for sets of animals to wander from the places in which they had come into existence. The newer theory of evolution was equally opposed to the notion of the appearance of similar animals at the same time on far-distant parts of the earth. For such reasons he proposed to reject the use of the word Contemporaneous as applied to rockbeds in different localities which contained the same fossils, and to replace it by the word Homotaxial, which meant no more than that the beds occupied corresponding places in the geological history of the earth. Huxley did not pretend that these arguments were entirely original: they represented the drift of the best geological opinion, and he seized hold of them and set them down as permanent geological truths.

In 1869, in a Presidential Address to the Geological Society, Huxley took up one of the burning questions of the day. In the early part of the century, the discoveries of geologists had been the occasion of great distress to those good people who clung to a literal interpretation of everything in the Bible. Long before the doctrine of evolution and the descent of man from lower animals had taken practical shape, there had been a battle royal between geologists who declared that the earth was many million years old, and had been inhabited at least by animals and plants for enormous periods, and those who clung to the traditional chronology which placed the date of creation only a few thousand years from now. The continued progress of geology, and the sturdy championship of it by men like Sedgwick, Chalmers, and Buckland, who were at the same time reputable theologians and distinguished men of science, had decided the battle in favour of the conclusions of science, and it was accepted generally that the earth was almost indefinitely old. At the same time, another and more strictly scientific dispute had been in progress. The older school of geologists, looking on the face of the world, and seeing it scarred by mighty fissures, displaying huge distortions of the beds in the crust, had argued that geological change had taken place by a series of mighty catastrophes. The tremendous results which they saw seemed to them only possible on the theory that unusual and gigantic displays of force had caused them. On the other hand, Hutton and Lyell attempted to find adequate explanation of the greatest changes in the slow forces which may be seen in operation at the present time. Slow movements of upheaval and depression, amounting at most to an inch or two in a century, may be shown to be actually in existence now, and such slow changes acting for very many centuries would account for the raising of continents above the sea, so that old sea-bottoms became the surface of the land, and for the depression of land areas so that new sedimentary rocks might be deposited upon them. They shewed how air and water slowly crumbled away the hardest rocks, and how rivers deepened their beds steadily but excessively slowly; and they held that while great catastrophic changes might occasionally have occurred, there was ample evidence of the present operation of forces which, granted sufficient time for their operation, would have made the crust of the earth such as it is. This doctrine of Uniformitarianism, of the action of similar forces in the past and present history of the earth, had almost completely triumphed over the older catastrophic views. As Huxley put it, the school of catastrophe put no limit to the violence of forces which had operated; the uniformitarians put no limit to the length of time during which forces had operated.

"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 development of the earth from a state in which its form, and the forces which it exerted, were very different from those which we now know.

"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."

But there was a third influence at work in geology, an influence which may best be described in Huxley's own words:

"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 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 a history of the 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 belching 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 of physical geography, sometimes that of geology. Again, the earth has a place in space and 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 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."

Huxley then proceeded to shew that uniformitarianism and catastrophism had neglected this last and most important branch of geology, the attempt to trace the interaction of causes which had brought the world into its present condition. He gave a striking display of the wide knowledge of his reading by going back to the foundation of this branch of modern science, and giving a masterly account of the then little-known treatise of Immanuel Kant, who in 1775 had written An Attempt to Account for the Constitutional and Mechanical Origin of the Universe upon Newtonian Principles. Next he declared that evolution embraced all that was sound in both catastrophism and uniformitarianism while rejecting the arbitrary limits and assumptions of both.

Finally he came to the great question to which these observations upon the existing schools of geology had led. The most distinguished physicist of the age, then Sir William Thomson, now Lord Kelvin, and Huxley's immediate successor in the Presidential Chair of the Royal Society, had stated that the English school of geology had assumed an impossible age for the earth. By physical reasonings, Thomson stated that he was able to prove "That the existing state of things on the earth—all geological history showing continuity of life—must be limited within some such period of time as one hundred million years." This pronouncement had been received with acclamation by those who feared the geological and biological sciences, as a sign of internal dissensions within the house of science. Huxley, then, as all through the latter part of his life, at once constituted himself the champion of science, and, taking Thomson's arguments one by one, shewed by a series of masterly deductions from known facts that there was a great deal to be said for the other side, and that physicists were as little certain as geologists could be of the exact duration of time that had elapsed since the dawn of life. His plea for more time since the cooling of the globe than physicists were willing to allow remains one of the classics of geological literature. But he carried the question much farther. The inference which was widely drawn by the enemies of evolution from the arguments of Sir William Thomson was that if geologists had overestimated the age of the cooled earth there was not time for the evolution of animals and plants to have taken place. Huxley pointed out a fact which should be quite obvious, but which even yet is frequently neglected. The evidence for the gradual appearance of life in the past history of the earth depends simply on the fact that the successive forms of life appear in successive strata, and the length of time taken for these changes simply depends upon the length of time which was taken up by the formation of the strata. Our only reason for supposing the evolution of life, made plain by fossil records, to have taken place very slowly is that geologists have stated that the deposition of the strata took place very slowly. Whether these strata were deposited slowly or less slowly, we know that the forms of life changed at the same rate.

"Biology takes her time from geology. The only reason we have for believing in the slow rate of 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 notion 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."

Perhaps, although this is now an old controversy, it is worth while to recall that the keenness of Huxley's language was not directed against Sir William Thomson, between whom and Huxley there was no more than the desire to argue out an interesting scientific question upon which their conclusions differed, but between Huxley and those outsiders who were always ready to turn any dubious question in science into an argument discrediting the general conclusions of science.

The last time that Huxley occupied the Presidential Chair of the Geological Society was in 1870, and he occupied his Presidential address by a review of the "old judgments" which he had given in the course of his first address in 1862. The address was entitled "Palaeontology and Evolution," and the most important part of it was a complete withdrawal of the fears he had expressed that geology would not supply definite evidence of the transformation of species. Important discoveries had come thick and fast; and, at least in the case of the higher vertebrates, he declared that, however one might "sift and criticise them," they left a clear balance in favour of the doctrine of the evolution of living forms one from another. But, with his usual critical spirit, examining arguments that bore against a conclusion for which he hoped almost more stringently than arguments apparently favourable to what he expected to be true, Huxley made an important distinction, the value of which becomes more and more apparent as time goes on. In the first flush of enthusiasm for Darwinism, zooelogists and palaeontologists allowed their zeal to outrun discretion in the formation of family trees. They examined large series of living or extinct creatures, and so soon as they found gradations of structure present, they arranged their specimens in a linear series, from the simplest to the most complex, and declared that the arrangement was a representation of the family tree. The fact that the line of descent apparently could have followed along the direction they suggested they were inclined to take as evidence that it had so followed. Huxley made the most careful distinction between what he called intermediate types and types with a right to be placed in linear order,

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 shews 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 a presumptive evidence in favour of evolution in general. The fact that Anoplotheridae are intermediate between pigs and ruminants does not tell us whether the ruminants have come from the pigs or the pigs from the ruminants, or both from Anoplotheridae, or whether pigs, ruminants, and Anoplotheridae; alike may not have diverged from some common stock.

A familiar instance will make the point at issue plain. Everyone knows that in many respects, in the structure of the skeleton, and the curve of the backbone, and in the development of the brain, the man-like monkeys, the gorilla and its allies, are intermediate between man and the lower monkeys. In the early days of evolution it was assumed frequently that the gorilla, etc., were therefore to be regarded as ancestors of man, and they appear as such in more than one well-known treatise on evolutionary biology. We now know that it is exceedingly probable that the gorilla and its allies, although truly intermediate types, and truly shewing a possible path of evolution from the brute to man, are not the actual ancestors of man, but cousins, descendants like man from some more or less remote common ancestor. And the tendency of recent advances in knowledge is more and more to throw stress on the value of Huxley's distinction, and to minimise confusion between "intermediate" and truly ancestral types.



CHAPTER VI

HUXLEY AND DARWIN

Early Ideas on Evolution—Erasmus Darwin—Lamarck—Herbert Spencer—Difference between Evolution and Natural Selection—Huxley's Preparation for Evolution—The Novelty of Natural Selection—The Advantage of Natural Selection as a Working Hypothesis—Huxley's Unchanged Position with regard to Evolution and Natural Selection from 1860 to 1894.

From our attempt to place together as much as possible of Huxley's geological work in the last chapter, it followed that we anticipated much that falls properly within this chapter. The year 1859, the date of publication of The Origin of Species, is a momentous date in the history of this century, as it was the year in which there was given to the world a theory that not only revolutionised scientific opinion, but altered the trend of almost every branch of thought. To understand this great change, and the part played in it by Huxley, it is necessary to be quite clear as to what Darwin did. In the first place, he did not invent evolution. The idea that all the varied structures in the world, the divergent forms of rocks and minerals and crystals, the innumerable trees and herbs that cover the face of the earth like a mantle, and all the animal host of creatures great and small that dwell on the land or dart through the air or people the waters,—that all these had arisen by natural laws from a primitive unformed material was known to the Greeks, was developed by the Romans, and even received the approval of early Christian Fathers, who wrote long before the idea had been invented that the naive legends of the Old Testament were an authoritative and literal account of the origin of the world. After a long interval, in which scientific thought was stifled by theological dogmatism, the theory of evolution, particularly in its application to animals, began to reappear, long before Darwin published The Origin of Species. Buffon, the great French naturalist, and Erasmus Darwin, the grandfather of Charles, had expressed in the clearest way the possibility that species had not been created independently, but had arisen from other species. Lamarck had worked out a theory of descent in the fullest detail, and regarded it as the foundation of the whole science of biology. He taught that the beginning of life consisted only of the simplest and lowest plants and animals; that the more complex animals and plants arose from these, and that even man himself had come from ape-like mammals. He held that the course of development of the earth and of all the creatures upon it was a slow and continuous change, uninterrupted by violent revolutions. He summed up the causes of organic evolution in the following propositions[D]:

"1. Life tends by its inherent forces to increase the volume of each living body and of all its parts up to a limit determined by its own needs.

"2. New wants in animals give rise to new movements which produce organs.

"3. The development of these organs is in proportion to their employment.

"4. New developments are transmitted to offspring."

He supported especially the last two propositions by a series of examples as to the effects of use and disuse; and the most famous of these, the theory that giraffes had produced their long necks by continually stretching up towards the trees on which they fed, is well known to everyone. However, the ingenious speculations of Lamarck were unsupported by a sufficient range of actual knowledge of anatomy, and lacked experimental proof. He entirely failed to convince his contemporaries; and Darwin himself, in a letter to Lyell, declared that he had gained nothing from two readings of Lamarck's book. There can be little doubt but that several Continental writers, in particular Haeckel, have exaggerated Lamarck's services to the development of the idea of evolution. On the other hand, Lyell, although he strongly opposed the ideas of Lamarck and some curious notions of progressional creation due to the great Agassiz, had prepared the way for Darwin by his advocacy of natural causes and slow changes in opposition to the catastrophic and miraculous views in vogue. Above all, Herbert Spencer had argued most strenuously in favour of evolution. Thus, in an important passage quoted by Mr. Clodd from the Leader of March 20, 1852, Spencer had written as follows:

"Those who cavalierly reject the theory of evolution, as not adequately supported by facts, seem quite to forget that their own theory is not supported by facts at all. Like the majority of men who are born to a given belief, they demand the most rigorous proof of any adverse belief, but assume that their own needs none. Here we find, scattered over the globe, vegetable and animal organisms numbering, of the one kind (according to Humboldt) some 320,000 species, and of the other, some 2,000,000 species (see Carpenter); and if to these we add the numbers of animal and vegetable species that have become extinct, we may safely estimate the number of species that have existed, and are existing, on the earth, at no less than ten millions. Well, which is the most rational theory about these ten millions of species? Is it most likely that there have been ten millions of special creations; or is it most likely that by continual modifications, due to change of circumstances, ten millions of varieties have been produced, as varieties are being produced still?... Even could the supporters of the development hypothesis merely shew that the origination of species by the process of modification is conceivable, they would be in a better position than their opponents. But they can do much more than this. They can shew that the process of modification has effected, and is effecting, decided changes in all organisms subject to modifying influences.... They can shew that in successive generations these changes continue, until ultimately the new conditions become the natural ones. They can shew that in cultivated plants, domesticated animals, and in the several races of men, such alterations have taken place. They can show that the degrees of difference so produced are often, as in dogs, greater than those on which distinctions of species have been founded. They can shew, too, that the changes daily taking place in ourselves—the facility that attends long practice, and the loss of aptitude that begins when practice ceases,—the strengthening of the passions habitually gratified, and the weakening of those habitually curbed,—the development of every faculty, bodily, moral, intellectual, according to the use made of it—are all explicable on this principle. And thus they can shew that throughout all organic nature there is at work a modifying influence of the kind they assign as the cause of these specific differences; an influence which, though slow in its action, does, in time, if the circumstances demand it, produce marked changes—an influence which, to all appearance, would produce in the millions of years, and under the great varieties of condition which geological records imply, any amount of change."

These and many other instances which might be brought together from the published writings of the half-century before the publication of the Origin, show conclusively that the idea of evolution was far from new, and that all through the first part of this century dissatisfaction with the doctrine of the fixity of species and of their miraculous creation was growing. The great contribution of Darwin was this: First, by his theory of natural selection, he brought together the known facts of variation, of struggle for existence, and of adaptation to varying conditions, in such a way that they provided men with a rational and known cause, a cause the operation of which could be seen, for the origin of species by means of preservation of favoured races. Next, as to the origin of species, he brought together not only proofs of the actual operation of natural selection, but a body of evidence in favour of the fact of evolution that was, beyond all comparison, more striking than had been adduced by any earlier philosophical or biological writer. He convinced naturalists that evolution was by far the most probable way in which the living world had come to be what it is, and he made them turn to examination of the animal and vegetable kingdoms with a lively hope that the past history of the living world was not an insoluble problem. Darwin's doctrine brought a new life into biological study, and the result of the incomparably greater bulk of investigation that followed the year 1859 was a continual increase of evidence in favour of the probability of evolution, until now the whole scientific world, and the majority of those who are unscientific, are content to accept evolution as the only reasonable explanation of the living world. It is well to remember that while Darwin, by bringing forward the theory of struggle for existence and resulting survival of the fittest, was the actual cause of the present assured position of evolution as a first principle of science, it by no means follows that the survival of the fittest has become similarly a first principle of science. At cross roads a traveller may choose the right path from a quite unsatisfactory reason. Darwin himself, in the act of bringing forward his own theory of natural selection, admitted the possibility of the co-operation of many other agencies in evolution, and at various times during the course of his life he was inclined to attach, now more now less, importance to these additional agencies. Huxley, as we shall soon come to see, never wavered in his adhesion to the facts of evolution after 1859; but, from first to last, regarded natural selection as only the most probable cause of the occurrence of evolution. Other naturalists, of whom the best-known are Weismann in Germany, Ray Lankester in England, and W.K. Brooks in America, have come to attach a continually increasing importance to the purely Darwinian factor of natural selection; while others again, such as Herbert Spencer in England, and the late Professor Cope and a large American school, have advocated more and more strongly the importance of what may be called the Lamarckian factors of evolution,—the inherited effects of increased or diminished use of organs, the direct influence of the environment, and so forth. From the fact that Darwin has persuaded the world of the truth of evolution, evolution is often called Darwinism; and in this historically just though scientifically inaccurate sense of the term, Huxley was a strict Darwinian, a Darwinian of the Darwinians. From the facts that, although natural selection had been formulated by several writers before Darwin, and had been simultaneously elaborated by Wallace and Darwin, the Origin of Species was the foundation of the modern acceptation of evolution, and natural selection was the key-note of the origin of species, natural selection may be called Darwinism with both historical and scientific accuracy; and in this sense of the term Huxley was a Darwinian; a convinced but free-thinking and broad-minded Darwinian, who was far from persuaded that his tenet had a monopoly of truth, and who delighted in shewing the distinctions between what seemed to him probable and what was proved, and in absorbing from other doctrines whatever he thought worthy to be absorbed. The present writer has thought it so important to distinguish between these two sides of the word Darwinism, that for the sake of clearness he has stated what he believes to be the truth of Huxley's relation to Darwin before beginning detailed exposition of it.

In consideration of Huxley's position before 1859, the most interesting feature of his zooelogical work is the gradual preparation that it was making in his mind for the doctrine of the Origin. He was like an engineer boring a tunnel through a mountain, but ignorant of how near he was to the pleasant valley on the other side; and, above all, ignorant how rapidly he was being met by a much more mighty excavation from the other side. To use what is perhaps a more exact simile: he was like a child with half the pieces of a puzzle-map, slowly linking them together as far as they would fit, and quite ignorant that presently the remaining half would suddenly be given him, and with almost no trouble would at once fit into the gaps he had necessarily left, and transform a meaningless pattern into a perfect and intelligible whole. Let us consider some of these map pieces. The ultimate picture was the conception of the whole world of life, past and present, as a single family tree growing up from the simplest possible roots, and gradually spreading out first into the two main branches of animals and plants, and then into the endless series of complicated ramifications that make up living and extinct animals and plants. Huxley was piecing together the scattered fragments, and gradually learning to see here and there whole branches, as yet separate at their lower ends, but in themselves shapely, and showing a general resemblance to one another in the gradual progression from simple to complex. The greatest of these branches that he had pieced together was the group of Medusae and their allies, now known as Coelenterates. He had formed similar branches for the Molluscs and minor branches for the Salps and Ascidians, and, in his general lectures on the whole animal kingdom, he had shadowed out the broad arrangement of the main divisions, or, as he called them, types. He had seen in each particular branch the clearest evidence of the laws of growth which had directed its development, and had realised that these laws of growth, consisting of gradual modifications of common typical structures, were identical in the different branches. He had taken clear hold of Von Baer's conception that the younger stages of different types were more alike than the adult stages, and here and there he had made comparisons between the younger stages or simplest forms of his different branches, and had shown that, without completely realising it, he was ready for the idea that just as the separate pieces could be arranged to form orderly branches, so the separate branches might come to be arranged as a single tree. And finally, in his lectures on "Protoplasm and Cells," and on the "Common Structure of the Animal and Plant Kingdoms," he had reached the conclusion that the two main divisions of the living world were formed of the same stuff, displayed in identical fashion the elementary functions of life, and were creatures of the same order. But, notwithstanding this close approach to modern conceptions, he was not an evolutionist. When, in public, he expressed deliberate convictions, these convictions were against the general idea of evolution, until very shortly before 1859. In this opposition he was supported partly by the critical scepticism of his mind, which in all things made him singularly unwilling to accept any theories of any kind, but chiefly from the fact that the books of the two chief supporters of evolutionary conceptions impressed him very unfavourably. Huxley writes:

"I had studied Lamarck attentively, and I had read the Vestiges with due care; but neither of them afforded me any good ground for changing my negative and critical attitude. As for the Vestiges, I confess that the book simply irritated me by the prodigious ignorance and thoroughly unscientific habit of mind manifested by the writer. If it had any influence on me at all, it set me against evolution; and the only review I ever have qualms of conscience about, on the ground of needless savagery is one I wrote on the Vestiges while under that influence. With respect to the Philosophie Zoologique, it is no reproach to Lamarck to say that the discussion of the species question in that work, whatever might be said for it in 1809, was miserably below the level of the knowledge of half a century later. In that interval of time, the elucidation of the structure of the lower animals and plants had given rise to wholly new conceptions of their relations; histology and embryology, in the modern sense, had been created; physiology had been reconstituted; the facts of distribution, geological and geographical, had been prodigiously multiplied and reduced to order. To any biologist whose studies had carried him beyond mere species-mongering, in 1850 one-half of Lamarck's arguments were obsolete, and the other half erroneous or defective, in virtue of omitting to deal with the various classes of evidence which had been brought to light since his time. Moreover his one suggestion as to the cause of the gradual modification of species—effort excited by change of conditions—was, on the face of it, inapplicable to the whole vegetable world. I do not think that any impartial judge who reads the Philosophie Zoologique now, and who afterwards takes up Lyell's trenchant and effective criticism (published as far back as 1830) will be disposed to allot to Lamarck a much higher place in the establishment of biological evolution than that which Bacon assigns to himself in relation to physical science generally—buccinator tantum".

On the other hand, Huxley's friendship with Darwin and with Lyell began to make him less certain about the fixity of species. He tells us that during his first interview with Darwin, which occurred soon after his return from the Rattlesnake, he

"expressed his belief in the sharpness of the lines of demarcation between natural groups and in the absence of transitional forms, with all the confidence of youth and imperfect knowledge. I was not aware at that time that he had been many years brooding over the species question; and the humorous smile which accompanied his gentle answer, that such was not altogether his view, long haunted and puzzled me."

An elaborate study of Lyell's works helped largely in destroying this youthful confidence, and a letter written by Lyell and quoted by Huxley in the chapter he communicated to Darwin's Life and Letters, states that in April, 1856, "when Huxley, Hooker, and Wollaston were at Darwin's last week they (all four of them) ran a tilt against species; further I believe, than they are prepared to go." Another quotation from Huxley's essay on The Reception of the Origin of Species will make it plain beyond all doubt that he was not a Darwinian before Darwin.



"Thus, looking hack into the past, it seems to me that my own position of critical expectancy was just and reasonable, and must have been taken up, on the same grounds, by many other persons. If Agassiz had told me that the forms of life which had successively tenanted the globe were the incarnations of successive thoughts of the Deity; and that He had wiped out one set of these embodiments by an appalling geological catastrophe as soon as His ideas took a more advanced shape, I found myself not only unable to admit the accuracy of the deductions from the facts of palaeontology, upon which this astounding hypothesis was founded, but I had to confess my want of means of testing the correctness of his explanation of them. And besides that, I could by no means see what the explanation explained. Neither did it help me to be told by an eminent anatomist that species had succeeded one another in time, in virtue of a 'continuously operative creational law'. That seemed to me to be no more than saying that species had succeeded one another in the form of a vote-catching resolution, with 'law' to please the man of science and 'creational' to draw the orthodox. So I took refuge in that thaetige Skepsis which Goethe has so well defined; and, reversing the apostolic precept to be all things to all men, I usually defended the tenability of the received doctrines when I had to do with the transmutationists, and stood up for the possibility of transmutation among the orthodox—thereby, no doubt, increasing an already current, but quite undeserved, reputation for needless combativeness."

What transformed Huxley's views and the views of his contemporaries who accepted Darwinism was not so much the evidence in favour of evolution contained in the Origin, as the illuminating doctrine of natural selection which for the first time supplied naturalists with a reasonable explanation of how evolution might have come about, both in the animal and vegetable kingdoms. As soon as this reason was provided them, they turned to the store of facts within their own knowledge, and rapidly arranged the evidence which had been lurking only partly visible in favour of the fact of evolution. It cannot be disputed that here and there earlier writers than Darwin and Wallace had suggested the possibility of natural selection acting upon existing variations so as to cause survival of the fittest. MacGillivray, the Scots naturalist, and the father of Huxley's companion on the Rattlesnake, had published suggestions which came exceedingly near to Darwin's theory. In 1831 Mr. Patrick Matthew had published a work on Naval Architecture and Timber, and in it had stated the essential principle of the Darwinian doctrine of struggle and survival. Still earlier, in 1813, a Dr. W.C. Wells, in a paper to the Royal Society on "A White Female, Part of whose Skin Resembles that of a Negro," had, as Darwin himself freely admitted, distinctly recognised the principle of natural selection—but applied it only to the races of man, and to certain characters alone. Finally, long before either of these, Aristotle himself had written, in Physics, ii., 8: "Why are not the things which seem the result of design, merely spontaneous variations, which, being useful, have been preserved, while others are continually eliminated as unsuitable?" None of these foreshadowings were supported by lengthy evidence, nor worked out into an elaborate theory; and it was not until Darwin had done this that we can say the birth of natural selection really took place. Huxley writes:

"The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present,—and which we call 'spontaneous,' because we are ignorant of their causation,—is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858."

But that suggestion is the central idea of the origin of species, and contains the quintessence of Darwinism.

Some weeks before the Origin was published, Darwin wrote to Huxley, sending him a copy of the work, and asking him for the names of eminent foreigners to whom it should be sent. In the course of his letter he wrote: "I shall be intensely curious to hear what effect the book produces on you," and it was clear that he had no very confident expectation of a favourable opinion. Huxley replied the day before the Origin was published, saying that he had finished the volume, and stating that it had completely convinced him of the fact of evolution, and that he fully accepted natural selection as a "true cause for the production of species." Darwin, in a letter to Wallace, telling of his doubts and fears concerning the reception of his book, had added the postscript: "I think I told you before that Hooker is a complete convert. If I can convert Huxley, I shall be content." When he received Huxley's letter he replied at once:

"Like a good Catholic who has received extreme unction, I can now sing Nunc Dimittis. I should have been more than contented with one quarter of what you have said. Exactly fifteen months ago, when I first put pen to paper for this volume, I had awful misgivings, and thought perhaps I had deluded myself, like so many have done; and I then fixed in my mind three judges, on whose decision I determined mentally to abide. The judges were Lyell, Hooker, and yourself. It was this which made me so excessively anxious for your verdict. I am now contented, and can sing my Nunc Dimittis."

The effect of the new theory on Huxley's mind has been expressed most fully and clearly by himself:

"I imagine that most of my contemporaries who thought seriously about the matter were very much in my own state of mind—inclined to say to Mosaists and Evolutionists, 'a plague on both your houses!' and disposed to turn aside from an interminable and apparently fruitless discussion to labour in the fertile fields of ascertainable fact. And I may, therefore, further suppose that the publication of the Darwin and Wallace papers in 1858, and still more that of the Origin in 1859, had the effect upon them of that of a flash of light which, to a man who has lost himself in a dark night, suddenly reveals a road which, whether it takes him straight home or not, certainly goes his way. That which we were looking for and could not find, was a hypothesis respecting the origin of known organic forms, which assumed the operation of no causes but such as could be proved to be actually at work. We wanted, not to pin our faith to that or any other speculation, but to get hold of clear and definite conceptions which could be brought face to face with facts and have their validity tested. The Origin provided us with the working hypothesis we sought. Moreover, it did us the immense service of freeing us for ever from the dilemma—refuse to accept the creation hypothesis, and what have you to propose that can be accepted by any cautious reasoner? In 1857 I had no answer ready, and I do not think that anyone else had. A year later, we reproached ourselves with dulness for being perplexed by such an enquiry. My reflection, when I first made myself master of the central idea of the Origin was, 'how exceedingly stupid not to have thought of that.' I suppose that Columbus's companions said much the same when he made the egg to stand on end. The facts of variability, of the struggle for existence, of adaptation to conditions, were notorious enough; but none of us had suspected that the road to the heart of the species problem lay through them, until Darwin and Wallace dispelled the darkness, and the beacon-fire of the Origin guided the benighted.

"Whether the particular shape which the doctrine of evolution, as applied to the organic world, took in Darwin's hands, would prove to be final or not, was, to me, a matter of indifference. In my earliest criticisms of the Origin I ventured to point out that its logical foundation was insecure so long as experiments in selective breeding had not produced varieties which were more or less infertile; and that insecurity remains up to the present time. But, with any and every critical doubt which my sceptical ingenuity could suggest, the Darwinian hypothesis remained incomparably more probable than the creation hypothesis. And if we had none of us been able to discern the paramount significance of some of the most patent and notorious of natural facts, until they were, so to speak, thrust under our noses, what force remained in the dilemma—creation or nothing? It was obvious that, hereafter, the probability would be immensely greater that the links of natural causation were hidden from our purblind eyes, than that natural causation should be unable to produce all the phenomena of nature. The only rational course for those who had no other object than the attainment of truth, was to accept 'Darwinism' as a working hypothesis, and see what could be made of it. Either it would prove its capacity to elucidate the fact of organic life, or it would break down under the strain. This was surely the dictate of common sense, and for once common-sense carried the day. The result has been that complete volte-face of the whole scientific world which must seem so surprising to the present generation. I do not mean to say that all the leaders of biological science have avowed themselves Darwinians; but I do not think that there is a single zooelogist, or botanist, or palaeontologist, among the multitude of active workers of this generation, who is other than an evolutionist profoundly influenced by Darwin's views. Whatever may be the ultimate fate of the particular theory put forth by Darwin, I venture to affirm that, so far as my knowledge goes, all the ingenuity and all the learning of hostile critics has not enabled them to adduce a solitary fact of which it can be said that it is irreconcilable with the Darwinian theory. In the prodigious variety and complexity of organic nature, there are multitudes of phenomena which are not deducible from any generalisation we have yet reached. But the same may be said of every other class of natural objects. I believe that astronomers cannot yet get the moon's motions into perfect accordance with the theory of gravitation."