greater number of them, so, in some cases, helping it to conquer and survive. Among its descendants, inheriting the modification and the accompanying habit, the thickening would be further increased in the same way—survival of the fittest tending ever to accelerate the process. Presently the horny nodes thus formed, hitherto defensive only in their effects, would by their prominence become offensive, would make the blows given more hurtful. And now Natural Selection, aiding more actively, would mould the nodes into spurs; the individuals in which the nodes were most pointed would be apt to survive and propagate; and the pointedness, generation after generation thus increased, would end in the well-adapted shape we see."
But on page 274 he says—
"Besides ascribing to Natural Selection the rise of various internal modifications of other classes than those above, we must ascribe some even of these to Natural Selection. It is so with the dense deposits which form thorns and the shells of nuts: these cannot have resulted from any inner reactions immediately called forth by outer actions, but must have resulted mediately through the effects of such outer actions on the species."
But if the accumulation of inborn variations is considered sufficient to account for the indurated tissues which form the shells of nuts and the thorns of plants, it is difficult to understand why it should be considered insufficient to account for the indurated tissues on the knuckles of the gorilla and on the wings of the Chaja screamer. The transformation of structures which were totally different into shells and thorns appears at the least to furnish as extreme examples of evolution as callosities and spurs, which, after all, are only specialized thickenings of the epidermis. As regards the gorilla, Mr. Spencer
