It has been laid down as a fundamental law of biogenesis that ontogeny (the development of the individual) and phylogeny (that of the race) must exactly correspond.... This law which I long held as well founded is absolutely and radically false. Attentive study of embryology shows us, in fact, that embryos have their own conditions suitable to themselves, very different from those of adults.
"In a word," M. de Quatrefages continues, "the learned Genevan professor rightly considers that, 'The ontogenesis of all organic beings without exception, is the normal result of all the various influences which operate upon such beings.'"
But it must, moreover, be noted that the story which embryology can be made to tell is by no means so plain as we might easily be led to suppose.
Thus, although snakes are held to be descended from lizards, and some of them have rudimentary legs even in the adult stage, others have no trace of limbs even in the egg, while they have vestiges[{195}] of gills, and thus would seem to be visibly linked to ancient water-dwelling ancestors, and not to far more recent land-dwellers. Again;[230] Amphibians (frogs, newts and the like) agree in some respects, as to the development of the germ, with mammals, differing in the same respects from reptiles and birds. But reptiles and birds are supposed to be a more recent development than Amphibia, and therefore should intervene between them and mammals on the genealogical tree. Moreover the eggs of one group of Amphibians are found to exhibit some remarkable resemblances to those of reptiles and birds, from which it would thus appear to have derived them, although on other grounds it is declared to be of an older stock than theirs. Most frogs, toads, and newts come out of the egg as tadpoles, furnished with gills and so breathing in water. This should signify that these creatures are descended from fish or fishlike ancestors. But one frog (Rana opisthodon) is never a tadpole even in the egg, from which he gets out by means of a special opener on his snout which he has somehow acquired. On the other hand certain newts[231] breed as tadpoles instead of in their mature form, which looks like an attempt to climb down the tree instead of up.
It will be remembered that the latter phrase was that used by Professor Milnes Marshall. Yet even he expressed himself strongly concerning the[{196}] exaggerations of Professor Haeckel on this subject. In his review of Haeckel's Anthropogenie,[232] after observing that many descriptions of human embryology have been based on observations of dogs, pigs, rabbits, or even chickens and dogfish, he thus continued regarding the book before him:
A student who relied on Professor Haeckel's description, would obtain an entirely erroneous idea of the development of the human embryo.... It is a matter for great regret that a book of 900 pages, bearing such a title, should be allowed to appear, in which the account of the actual development of the human embryo is so inadequate or even erroneous.
Far more fundamental, however, is a remark of Mr. Mivart's, that if, as Darwinians say, the development of the individual is an epitome of that of the species, the latter must like the former be due to the action of definite innate laws unconsciously carrying out definite preordained ends and purposes. For although cells or embryos may be indistinguishable from one another, and may appear to us identical in constitution, their differences are absolute. Each is determined to be one sort of animal and no other, and can live at all only on condition of developing towards the prescribed form.—Therefore, whatever evidence the embryonic forms may be supposed to afford in support of Evolution, they have nothing in common with the haphazard process of Natural Selection.[{197}]
And here again Professor Huxley found himself obliged to enter his caveat, and to intimate his opinion that some of his friends were inclined to build too confidently upon this foundation. As his biographer Professor Weldon writes in the Dictionary of National Biography:
Darwin had suggested an interpretation of the facts of embryology which led to the hope that a fuller knowledge of development might reveal the history of all the great groups of animals at least in its main outlines. This hope was of service as a stimulus to research, but the attempt to interpret the phenomena observed led to speculations which were often fanciful and always incapable of verification. Huxley was keenly sensible of the danger attending the use of a hypothetical explanation, leading to conclusions which cannot be experimentally tested, and he carefully avoided it.... In the preface to the Manual of the Comparative Anatomy of Invertebrated Animals, he says: "I have abstained from discussing questions of ætiology,[233] not because I underestimate their importance, or am insensible to the interest of the great problem of Evolution, but because, to my mind, the growing tendency to mix up ætiological speculations with morphological generalizations will, if unchecked, throw Biology into confusion."
Accordingly, Huxley himself based his faith in Evolution on palæontological evidence, and attempted to decide the precise course it had followed only "in the few cases where the evidence seemed[{198}] to him sufficiently complete." This line of enquiry we have still to pursue, but meanwhile, it is evident that the phenomena we have been considering, failing to meet the approval of so thorough-going an Evolutionist as he undoubtedly was, cannot be said to furnish convincing scientific evidence in favour of Darwinism.