Page - 151 - in The Origin of Species

EFFECTS OF USE AND DISUSE 151 which subsists generally between the fauna of Europe and of North America." On my view we must suppose that American animals, having in most cases ordinary powers of vision, slowly migrated by successive generations from the outer world into the deeper and deeper recesses of the Ken- tucky caves, as did European animals into the caves of Europe. We have some evidence of this gradation of habit; for, as Schiodte remarks, "We accordingly look upon the subterranean faunas as small ramifications which have pene- trated into the earth from the geographically limited faunas of the adjacent tracts, and which, as they extended them- selves into darkness, have been accommodated to surround- ing circumstances. Animals not far remote from ordinary forms, prepare the transition from light to darkness. Next follow those that are constructed for twilight; and, last of all, those destined for total darkness, and whose formation is quite peculiar." These remarks of Schiodte's, it should be understood, apply not to the same, but to distinct species. By the time that an animal had reached, after numberless generations, the deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and natural selection will often have effected other changes, such as an increase in the length of the antennae or palpi, as a compen- sation for blindness. Notwithstanding such modifications, we might expect still to see in the cave-animals of America, affinities to the other inhabitants of that continent, and in those of Europe to the inhabitants of the European conti- nent. And this is the case with some of the American cave- animals, as I hear from Professor Dana ; and some of the European cave-insects are very closely allied to those of the surrounding country. It would be difficult to give any ra- tional explanation of the affinities of the blind cave-animals to the other inhabitants of the two continents on the ordi- nary view of their independent creation. That several of the inhabitants of the caves of the Old and New Worlds should be closely related, we might expect from the well- known relationship of most of their other productions. As a blind species of Bathyscia is found in abundance on shady rocks far from caves, the loss of vision in the cave-species of this one genus has probably had no relation to its dark