Chap. V.] EFFECTS OF USE AND DISUSE. Ill 



generally between the fauna of Europe and of North America." 

 On my view we must suppose that American animals, having in 

 mcst cases ordinary powers of vision, slowly migrated by successive 

 generations from the outer world into the deeper and deeper re- 

 cesses 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 adja- 

 cent 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. Nest follow those that are constructed for twi- 

 light ; and, last of all, those destined for total darkness, and whose 

 formation is quite peculiar." These remarks of Schibdte'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. Notwithstand- 

 ing such modifications, we might expect still to see in the cave- 

 animals of America, affinities to the other inhabitants of that con- 

 tinent, 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 

 ihe 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 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 habitation ; for it 

 is natural that an insect already deprived of vision should readily 

 become adapted to dark caverns. Another blind genus (Anoph- 

 thalmus) offers this remarkable peculiarity, that the species, as 

 Mr. Murray observes, have not as yet been found anywhere except 

 in caves ; yet those which inhabit the several caves of Europe and 

 America are distinct ; but it is possible that the progenitors of these 

 several species, whilst they were furnished with eyes, may formerly 



