It was with a view of the animal kingdom not much clearer than this that Huxley began his work on the Medusae of the tropic seas. He began to study them no doubt simply because they were among the most abundant of the animals that could be obtained from the ship. He made endless dissections and drawings, and, above all, studied their minute anatomy with the microscope. They were all placed among Cuvier"s _Radiata_, but, as Huxley said in the first line of his memoir:
"Perhaps no cla.s.s of animals has been investigated with so little satisfactory and comprehensive result, and this not for the want of patience and ability on the part of the observers, but rather because they have contented themselves with stating matters of detail concerning particular genera and species, instead of giving broad and general views of the whole cla.s.s, considered as organised upon a given type, and inquiring into its relations with other families."
He found that fully developed Medusae consisted each of a disc with tentacles and vesicular bodies at the margins, a stomach, and ca.n.a.ls proceeding from it, and generative organs. He traced this simple common structure through the complications and modifications in which it appeared in the different groups of Medusae, in all this work bringing out the prevailing features of the anatomy in contrast to the individual peculiarities. He shewed that microscopically all the complicated systems of ca.n.a.ls and organs were composed of two "foundation-membranes," two thin webs of cells, one of which formed the outermost layer of the body, while the inner formed the lining of the stomach and ca.n.a.ls in the thinner parts of the body, such as the edges of the umbrella-like disc, and towards the ends of the tentacles. These thin webs formed practically all the body. In the thicker parts there was interposed between them an almost structureless layer of jelly, placed like padding between the lining and the cloth of a coat. He shewed that blood-vessels and blood were absent, in which he has been confirmed by all other observers. He declared more doubtfully against the existence of a special nervous system, and it was not until long after, when the methods of microscopic investigation were much more perfect, that the delicate nerve-cells and nerve-fibres, which we now know to exist, were discovered.
Having thus shewn the peculiar organisation of the group he turned to seek out its allies among other families. The Medusae consisted essentially of two membranes inclosing a variously shaped cavity inasmuch as all its organs were so composed. The generative organs were external, being variously developed processes of the two membranes. The peculiar organs called thread-cells--poisoned darts by the discharge of which prey could be paralysed--were universally present. What other families presented these peculiarities?
There are to be found abundantly in sea-water, and less frequently in fresh water, innumerable forms of animal life called Zoophytes or animal plants because they occur as encrusting ma.s.ses like lichens, or branched forests like moss, on the surface of stones and sh.e.l.ls. A common habit gave this set of creatures their common name; but, although they were grouped together, there was no greater affinity among them than there is racial affinity among people who clothe themselves for an evening party in the same conventional dress. Huxley examined a large number of these, and picked out from them two great families of polyps, the Hydroid and Sertularian polyps, which each consist of colonies of creatures very much like the little fresh-water hydra. He shewed that the tubular body of these and the ring of tentacles surrounding the mouth were composed of the same two foundation-membranes of which all the organs of Medusae are composed.
He found in them the poisoned arrows or thread-cells of the Medusae, and the same external position of the reproductive organs. And, lastly, he separated from all other creatures, and a.s.sociated with his new group, some of the strangest and most beautiful animals of the tropic seas, known to science as the Physophoridae and the Diphyidae.
The best-known of these is the "Portuguese man-of-war," the body of which consists of a large pear-shaped vesicle which floats on the water like a bladder. From the lower part of this depend into the water large and small nutritive branches, each ending in a mouth surrounded by a circle of waving tentacles armed with batteries of thread-cells, while another set of hanging protrusions bear the grape-like reproductive organs. On the upper surface of the bladder is fixed a purple sail of the most brilliant colour, by which the floating creature is blown through the water. When the weather is rough, the bladder empties, and the creature sinks down into the quiet water below the waves, to rise again when the storm is over. This, and its equally wonderful allies, Huxley showed to be a complicated colony of hydra-like creatures, each part being composed of two membranes, and therefore essentially similar to Medusae. Thus, by a great piece of constructive work, an a.s.semblage of animals was gathered into a new group and shewn to be organised upon one simple and uniform plan, and, even in the most complex and aberrant forms, reducible to the same type. The group, and Huxley"s conception of its structure, are now absolutely accepted by anatomists, and have made one of the corner-stones of our modern idea of the arrangement of the animal kingdom. With the exception of sponges, concerning the exact relations of which there is still dispute, and of a few sets of parasitic and possibly degenerate creatures, all animals, the bodies of which are multicellular, from the simple fresh-water hydra up to man, are divided into two great groups. The structure of the simpler of these groups is exactly what Huxley found to be of importance in the Medusae. The body wall, from which all the organs protrude, consists merely of a web of cells arranged in two sheets or membranes, and the single cavity consists of a central stomach, surrounded by these membranes, the cavity remaining simple or giving rise to a number of branching ca.n.a.ls. The members of this great division of the animal kingdom are the creatures which Huxley selected and placed together, with the addition of the sea-anemones and the medusa-like Ctenophora, which, indeed, he mentioned in his memoir as being related to the others, but reserved fuller consideration for a future occasion. This group is now called the Clenterata, the name implying that the creatures are simply hollow stomachs, and it is contrasted in the strongest way with the group Clomata, in which are placed all the higher animals, from the simplest worm up to man; animals in which, in addition to the two foundation-membranes of the Clenterata, there is a third foundation-membrane, and in which, in addition to the simple stomach cavity with its offshoots, there is a true body-cavity or clome, and usually a set of s.p.a.ces and channels containing a blood-fluid. The older method of naming groups of animals after some obvious superficial character lingered on for some years in text-books and treatises, but in this memoir the young ship-surgeon had replaced it by the modern scientific method of grouping animals together only because of real ident.i.ty of structure.
There is yet left to be noticed perhaps the most wonderful of all the ideas in this first memoir by Huxley. In the course of describing the two foundation membranes of the Medusae he remarks:
"It is curious to remark, that throughout, the outer and inner membranes appear to bear the same physiological relation to one another as do the serous and mucous layers of the germ: the outer becoming developed into the muscular system, and giving rise to the organs of offence and defence: the inner on the other hand appearing to be more closely subservient to the purposes of nutrition and generation."
In the whole range of science it would be difficult to select an utterance more prophetic of future knowledge than these few words.
Huxley had been reading the investigations of Von Baer into the early development of back-boned animals. He had learned from them the great generalisation, that the younger stages of these animals resemble one another more closely than the adult stages, and that in an early stage in the development of all these animals the beginning of the embryo consists of two layers of cells, in fact of two foundation-membranes, one forming specially the wall of the future digestive ca.n.a.l, the other forming the most external portion of the future animal. In these days nothing could have seemed a remoter or more unlikely comparison than one inst.i.tuted between Medusae and the embryonic stages of back-boned animals. But Huxley made it, not allowing the evidence brought before his reason to be swamped by preconceived ideas. At the time he did no more than to make the comparison. It was much later that the full importance of it became known, when more extended work on the embryology of vertebrates and of the different groups of the invertebrates had made it plain that the two foundation-membranes of Huxley occur in all animals from the Medusae up to man. In the group of Clenterata the organisation remains throughout life as nothing more than a folding in and folding out of these membranes. The early stages of all the higher animals similarly consist of complications of the two membranes; but later on there is added to them a third membrane. Thus the group that Huxley gathered together comprises those animals that as adults remain in a condition of development which is pa.s.sed through in the embryonic life of all higher animals. The immense importance of this conclusion becomes plain, and the conclusion itself seems obvious, when seen in the light of the doctrine of descent. The group of Clenterata represents a surviving, older condition in the evolution of animals. Huxley himself, when on the _Rattlesnake_, regarded evolution only as a vague metaphysical dream, and he made the comparison which has been described without any afterthought of what it implied. In this we have the earliest authentic instance of the peculiar integrity of mind which was so characteristic of him in his dealings with philosophy and tradition. He never allowed any weight of authority or any apparent disturbance of existing ideas to alter the conclusions to which his reason led him. This intellectual courage made him fitted to be the leader in the battle for evolution and against traditional thought, and we shall find again and again in consideration of his work that it was the keynote of his life.
CHAPTER IV
EARLY DAYS IN LONDON
Scientific Work as Unattached Ship-Surgeon--Introduction to London Scientific Society--Translating, Reviewing, and Lecturing--Ascidians--Molluscs and the Archetype--Criticism of Pre-Darwinian Evolution--Appointment to Geological Survey.
The _Rattlesnake_ was paid off at Chatham on November 9, 1850. In the natural course of events Huxley would have been appointed before long to active service upon another ship. But he had no intention of relapsing into the position of a mere navy doctor; he had acc.u.mulated sufficient scientific material to keep him employed on scientific investigation for years, and so he applied to the Admiralty to "be borne on the books" of H.M.S. _Fisgard_ at Woolwich,--that is to say, to be appointed a.s.sistant-surgeon to the ship "for particular service," so that he should not be compelled to live on board, but might remain in town, and, with free access to libraries and museums, work up the observations he had made on the _Rattlesnake_ into serious and substantial contributions to science. His request was granted, largely by the aid of his old chief, Sir W. Burnett, who continued to take the most useful interest in the young man he had originally nominated to the service. In a letter to him Huxley described the investigations which he desired to continue as being chiefly those on "the anatomy of certain Gasteropod and Pteropod Mollusca, of Firola and Atlantis, of Salpa and Pyrosoma, of two new Ascidians, namely, Appendicularia and Doliolum, of Sagitta and certain Annelids, of the auditory and circulatory organs of certain transparent Crustacea, and of the Medusae and Polyps." His request was granted, and for the next three years Huxley lived in London with his brother, on the exiguous income of an a.s.sistant-surgeon, and devoted himself to research. He became almost at once of the first rank among English anatomists. The result of the paper on Medusae in the _Transactions of the Royal Society_ was that he was elected a Fellow of the Society on June 5, 1851, and a year later received a Royal Medal of the Society. He made many warm friendships both among the older and the younger generations of scientific men. In his obituary notice of Huxley, Sir Michael Foster wrote:
"By Edward Forbes, in whose nature there was much that was akin to his own, and with whom he had some acquaintance before his voyage, he was at once greeted as a comrade, and with Joseph Dalton Hooker, to whom he was drawn at the very first by their common experience as navy surgeons, he began an attachment which, strengthened by like biological aspirations, grew closer as their lives went on. In the first year after his return, in the autumn of 1851, he made the acquaintance of John Tyndall at the meeting of the British a.s.sociation at Ipswich, and the three, Hooker, Huxley, and Tyndall, finding how much in common were all their scientific views and desires, formed then and there a triple scientific alliance."
Repeated efforts were made by these three, and by more influential friends, to induce the Admiralty to contribute to the expense of publishing Huxley"s scientific results, as they had given a pledge to encourage officers who had done scientific work. These efforts lasted unavailingly for nearly three years, and then, as Huxley says: "The Admiralty, getting tired, I suppose, cut short the discussion by ordering me to join a ship, which thing I declined to do, and, as Rastignac, in the _Pere Goriot_, says to Paris, I said to London, _ nous deux_." This light phrase conceals a courageous and momentous decision. He was absolutely without private resources, and having abandoned his professional work he had no salary of any kind. For a year or so he supported himself by writing reviews and popular scientific articles, striving all the time not only to gain his bread but to continue his scientific work and make it known to the public.
He desired to get a professorship of physiology or of comparative anatomy, and as vacancies occurred he applied, but unsuccessfully. At the same time, he tells us, he and his friend, John Tyndall, were
"candidates, he for the Chair of Physics, and I for that of Natural History in the University of Toronto, which, fortunately, as it turned out, would not look at either of us. I say fortunately, not from any lack of respect for the University of Toronto; but because I soon made up my mind that London was the place for me, and hence I have steadily declined the inducements to leave it which have at various times been offered."
In these early years in London Huxley"s work was most varied. A large number of anonymous articles by him appeared in the _Literary Gazette_, and in other periodicals. He a.s.sisted to remove the insular narrowness from English scientific work by translating many foreign memoirs. With the collaboration of Mr. Henfrey, he edited a series of scientific memoirs, all of which were translated from foreign languages, and many by his own pen. With the a.s.sistance of Mr. George Busk he made a translation of Kolliker"s _Histology_, a great treatise on microscopic anatomy which played a large part in the development of the modern English schools of anatomy and physiology. He made some valuable contributions to Todd and Bowman"s _Cyclopaedia of Anatomy_, an elaborate publication now nearly forgotten and practically superseded, but which was the standard anatomical work of the middle of this century. He was unable to progress rapidly with his work upon oceanic Medusae, as he was uncertain how to have it published; the Admiralty refused to a.s.sist, and it was too lengthy for publication in the volumes of the learned Societies. As a matter of fact, he did not publish it until 1858, when it appeared as a separate memoir. To the _Quarterly Journal of Microscopical Science_ and to the _Transactions of the Royal and Linnaean Societies_ he contributed a large number of memoirs dealing with the microscopic anatomy and relationships of invertebrates, and, lastly, he gave a series of addresses at the Royal Inst.i.tution, which had been founded as a means by which leading men of science might give accounts of their work to London society. Abstracts of these lectures are published in the early volumes of the _Proceedings of the Royal Inst.i.tution_ and are interesting as shewing the kinds of zoological subjects which were attracting the attention of Huxley and which he considered of sufficient interest and importance to bring to the notice of the general public. The first of these lectures, and probably the first given in public by Huxley, occurred on April 30, 1852, and was ent.i.tled "Animal Individuality."
The problem as to what is meant by an individual had been raised in his mind by consideration of many of the forms of marine life, notably compound structures like the Portuguese man-of-war, and creatures like the salps, which form floating chains often many yards in length. He explained that the word _individual_ covers at least three quite different kinds of conceptions. There is, first, what he described as arbitrary individuality, an individuality which is given by the mind of the observer and does not actually exist in the thing considered. Thus a landscape is in a sense an individual thing, but only so far as it is a particular part of the surface of the earth, isolated for the time in the mind of the person looking at it. If the observer shift his position, the range of the landscape alters and becomes something else. Next there are material, or practically accidental individual things, such as crystals or pieces of stone; and, lastly, there are living individuals which, as he pointed out, were cycles. All living things are born into the world, grow up, and die, and it was to the cycle of life, from the egg to the adult which produces eggs, that he gave the name individual. In a simple animal like Hydra there is no difficulty in accepting this plain definition of individuality; but Huxley went on to compare with Hydra a compound creature like the Portuguese man-of-war, which really is composed of a colony of Hydra-like creatures, the different members of the colony being more or less altered to serve different functions. All these have come from the branching of a single simple creature produced from an egg, and to the whole colony Huxley gave the name of zoological individual. The salps give a still wider interpretation to this view of individuality. The original salp produced from the egg gives rise to many salps, which may either remain attached in a chain, or, breaking away from one another, may live separately. Huxley extended the use of the word _individual_ so as to include as a single zoological individual the whole set of creatures cohering in chains or breaking apart, which had been produced by budding from the product of a single egg-cell. This subtle a.n.a.lysis of ideas delighted and interested his contemporaries, and the train of logical examination of what is meant by individuality has persisted to the present time. Like all other zoological ideas, this has been considerably altered by the conception of evolution. Zoologists no longer attempt to stretch logical conceptions until they fit enormous and different parts of the living world. They recognise that the living world, because it is alive, is constantly changing, and that living things pa.s.s through different stages or kinds of individuality in the course of their lives. A single egg-cell is one kind, perhaps the simplest kind, of zoological individual; when it has grown up into a simple polyp it has pa.s.sed into a second grade of individuality; when, by budding, the polyp has become branched, a third grade is reached, and when the branches have become different, in obedience to the different purposes which they are to serve in the whole compound creature, a still further grade is reached. Huxley"s attempt to find a meaning for individuality that would apply equally to a single simple creature, to a compound creature, and to the large number of separate creatures, all developed by budding from one creature, is a striking instance of his singular capacity for bringing apparently dissimilar facts into harmony, by finding out the common underlying principle, and, although we no longer accept this particular conclusion, we cannot fail to notice in it the peculiar powers of his mind.
A second and even more interesting Royal Inst.i.tution lecture dealt with the "Ident.i.ty 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 ma.s.ses 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 Cla.s.se 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 zoology, 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 b.u.t.terflies, but by a process of s.e.xual breeding produced young which grew into the ordinary adults, and that these adults, as indeed they do, gave rise to caterpillars by s.e.xual 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 s.e.xual 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 s.e.xual generations. The s.e.xual 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 zoological 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 quant.i.ty of an allied Ascidian, Pyrosoma, which had received its name from its phosph.o.r.escence.
"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 phosph.o.r.escence was intermittent, periods of darkness alternating with periods of brilliancy. The light commenced in one spot, apparently on the surface of one of the zooids, 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 ma.s.s was dark again. Friction at any point induces the light at that point, and from thence the phosph.o.r.escence 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 seash.o.r.e. 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 Clenterate.
Mertens, another distinguished zoologist, had declared that "the relation of this animal with the Pteropods (a peculiar group of molluscs) is unmistakable"; while Muller, 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 ca.n.a.l, 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 zoologists 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 zoology 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 sh.e.l.l-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 h.o.m.ologues 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 h.o.m.ologous. 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 sh.e.l.l-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 h.o.m.ologous 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 Kolliker, 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 sh.e.l.l. 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 zoology 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 zoologists 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 zoological 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 Inst.i.tution in 1854 and 1855, the one on "The Common Plan of Animal Forms," the other on "The Zoological 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, ent.i.tled _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 zoologists 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 pa.s.s 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 a.s.sumed 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 a.s.sured, 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 Inst.i.tution, choosing as the t.i.tle 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.
[Ill.u.s.tration: THOMAS HENRY HUXLEY, 1857 Reproduced by permission from _Natural Science_, vol. vii., No. 42]
"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 pa.s.sing 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 Kolliker 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 a.s.sistance 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 ident.i.ty 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 a.s.sociation 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.