133 EFFECTS OF USE AND DISUSE. 



the caves of Europe. We have some evidence of this gra- 

 flation of habit; for, as Schiodte remarks: " We accord- 

 ingly look upon the subterranean faunas as small ramifica- 

 tions which have penetrated into the earth from the geo- 

 graphically limited faunas of the adjacent tracts, and 

 which, as they extended themselves into darkness, have 

 been accommodated to surrounding circumstances. Ani- 

 mals not far remote from ordinary forms, prepare the tran- 

 sition 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 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 

 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' 

 antennse 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 inhabit- 

 ants 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 prob- 

 ably had no relation to its dark habitation; for it is natu- 

 ral that an insect already deprived of vision should readily 

 become adapted to dark caverns. Another blind genus 

 (Anophthalmus) offers his 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 



