Thomas Henry Huxley; A Sketch Of His Life And Work

by Sir P. Chalmers Mitchell

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 Kölliker, 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 Encyclopædia 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 zoölogy 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 zoölogists 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 zoölogical 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 Zoölogical 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 Medusæ 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 zoölogists 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 Palæontologist 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 palæontological."