124 EFFECTS OF USE AND D1SUSF. 



eyes were lustrous and of large size ; and these animals, as 

 I am informed by Professor Silliman, after having been ex- 

 posed for about a month to a graduated light, acquired a 

 dim perception of objects. 



It is difficult to imagine conditions of life more similar 

 than deep limestone caverns under a nearly similar climate ; 

 so that, in accordance with the old view of the blind ani- 

 mals having been separately created for the American and 

 European caverns, very close similarity in their organiza- 

 tion and affinities might have been expected. This is cer- 

 tainly not the case if we look at the two whole faunas ; and 

 with respect to the insects alone, Schiodte has remarked : 

 "We are accordingly prevented from considering the entire 

 phenomenon in any other light than something purely local, 

 and the similarity which is exhibited in a few forms between 

 the Mammoth Cave (in Kentucky) and the caves in Car- 

 niola, otherwise than as a very plain expression of that 

 analogy which subsists generally between the fauna of 

 Europe and of North America." On my view we must sup- 

 pose 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 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 dark- 

 ness. 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 dis- 

 tinct 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 antennas 

 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 



