Page:Popular Science Monthly Volume 16.djvu/119

 arising out of "the mass of animal life to be dealt with," is a supposition that could only occur to a mind altogether unacquainted with anatomical science. The marvel always is, not the accidental similarity of organs, due to the exigencies of their performing similar functions, but the adaptation of anatomically homologous organs to the performance of widely different functions. To take only one instance by way of illustration. Where is the "necessity" that no one among the many species of bats should not have the wing formed in any other way than by the highly peculiar and distinctive modification of the hand? Or where is the "necessity" that all the still greater number of species of birds should have their wings formed by another highly peculiar and equally distinctive modification of the arm? Both structures serve equally well for flight; as, indeed, do the wings of insects and did the wings of the pterodactyl. So far, then, as the exigencies arising out of "the mass of animal life to be dealt with" are concerned, there is no reason why these four types of wings should not occur indiscriminately among the four classes of animals in question—and this even if we follow our author in confining the possibilities of creative invention to the anatomical structures of which we are cognizant. This, of course, is but a general refutation. The absurdity of the argument from "necessity" becomes the more apparent the more numerous and more minute the homologies of structure are found to be within the limits of the same type, without ever transgressing on the equally numerous and minute homologies of any other type. But the fact that homologies never thus commingle—that no one of a vast congeries of organs characteristic of one group of organisms ever appears in any other group of organisms—this fact is of such overwhelming force as evidence of genetic descent, that its supposed failure of application in one solitary instance was, as Sir Charles Lyell wisely observed, to his mind the strongest argument against evolution with which he had met. This solitary case of failure had reference to the eye of a mollusk (the cuttle-fish), which was alleged to be anatomically similar to the eye of a true fish. The allegation proved to be wholly false; but, so far as any "necessity" arising from the difficulty of inventing new forms is concerned, there is no reason why the allegation should not have been true.

Our reviewer next treats of the argument from embryology, and in doing so his ideas present that same crudity of cast which gives to his whole essay its grotesque character. He says: "Certainly these remarks are exceedingly curious, and even in a sense imposing. . . . But these resemblances, be they never so close, infer no real connection between the objects thus heterogeneously associated. It is not pretended that the objects compared together are ever entirely alike—that the unborn young of the higher animal is, at any stage of its development, identical with any of the lower animals, but only that some of the features of the one are like the analogous features of the