logic, the argument from stability as Wallace applies it to the case of specific characters, is incompatible with his argument that useless generic characters may originally have been useful specific characters. It can scarcely be questioned that the transmutation of a species into a genus must, as a rule, have allowed time enough for a newly acquired--i.e. peculiar specific-character--to show some signs of undergoing degeneration, if, as supposed, the original cause of its development and maintenance was withdrawn when the parent species began to ramify into its species-progeny. Yet, as Darwin says, "it is notorious that specific characters are more variable than generic[132]." So that, upon the whole, I do not see how on grounds of general reasoning it is logically possible to maintain Mr. Wallace's distinction between specific and generic characters in respect of necessary utility. [132] _Origin of Species_, p. 122. But now, and lastly, we shall reach the same conclusion if, discarding all consideration of general principles and formal reasoning, we fasten attention upon certain particular cases, or concrete facts. Thus, to select only two illustrations within the limits of genera, it is a diagnostic feature of the genus _Equus_ that small warty callosities occur on the legs. It is impossible to suggest any useful function that is now discharged by these callosities in any of the existing species of the genus. If it be assumed that they must have been of some use to the species from which the genus originally sprang, the assumption, it seems to me, can only be saved by further assuming that in existing species of the genus these callosities are in a vestigial condition--i. e. that in the original or parent species they performed some function which is now obsolete. But against these assumptions there lies the following fact. The callosities in question are not similarly distributed through all existing species of the genus. The horse has them upon all his four legs, while other species have them only upon two. Therefore, if all specific characters are necessarily due to natural selection, it is manifest that these callosities are _not_ now vestigial: on the contrary, they _must_ still be--or, at best, have recently been--of so much importance to all existing species of the genus, that not only is it a matter of selection-value to all these species that they should possess these callosities; but it is even a matter of selection-value to a horse that he should possess four of them, while it is equally a matter of selection-value to the ass that he should possess only two. Here, it seems to me, we have once more the doctrine of the necessary utility of specific characters reduced to an absurdity; while at the same time we display the incoherency of the distinction between specific characters and generic characters in respect of this doctrine. For the distinction in such a case amounts to saying that a generic character,