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



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 ac- 

 cordingly look upon the subterranean faunas as small 

 ramifications which have penetrated into the earth 

 from the geographically limited faunas of the adja- 

 cent tracts, and which, as they extended themselves 

 into darkness, have been accommodated to surround- 

 ing circumstances. Animals not far remote from or- 

 dinary 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 dark- 

 ness, 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 gener- 

 ations, 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 antennse or 

 palpi, as a compensation for blindness. ISTotwithstand- 

 ing 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 Eu- 

 ropean cave-insects are very closely allied to those of 

 the surrounding country. It weuld be difficult to give 

 any rational explanation of the affinities of the blind 

 cave-animals to the other inhabitants of the two con- 

 tinents on the ordinary view of their independent cre- 

 ation. That several of the inhabitants of the caves 



