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 



