172 EFFECTS OF USE AND DISUSE. [Chap. V. 



deeper recesses of the Kentucky 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 penetrated 

 into the earth from the geographically limited faunas 

 of the adjacent tracts, and which, as they extended 

 themselves into darkness, have been accommodated to 

 surrounding 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 Schioclte'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 

 antenna? or palpi, as a compensation 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 continent. 

 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 rational explanation of the affinities of the 

 blind cave-animals to the other inhabitants of the two 

 continents on the ordinary view of their independent 

 creation. That several of the inhabitants of the caves 



