Part 2 (2/2)
”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 s.h.i.+p 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 relations.h.i.+p 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 relations.h.i.+p 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 relations.h.i.+ps 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 fas.h.i.+on 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 fas.h.i.+on, 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 fas.h.i.+onable 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 fas.h.i.+on 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.
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