LAWS OF VARIATION 197 



may be attributed to disuse. In one of the blind ani- 

 mals, namely, the cave-rat (Neotoma), two of which were 

 captured by Professor Silliman at above half a mile dis- 

 tance from the mouth of the cave, and therefore not in 

 the profoundest depths, the eyes were lustrous and of 

 large size; and these animals, as I am informed by Pro- 

 fessor Silliman, after having been exposed for about a 

 month to a graduated light, acquired a dim perception 

 of objects. 



It is difficult to imagine conditions of life more sim- 

 ilar than deep limestone caverns under a nearly similar 

 climate; so that, in accordance with the old view of the 

 bliud animals having been separately created for the 

 American and European caverns, very close similarity 

 in their organization and affinities might have been ex- 

 pected. This is certainly 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 Carniola, 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 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 Kentucky caves, as did European animals into the 

 caves of Europe. We have some evidence of this grada- 

 tion of habit; for, as SehioJte remarks, "We accordingly 

 look upon the subterranean faunas as small ramifications 



