DISCREPANCIES. 



water Treatise," contend that they form no por- 

 tion of the fauna now in existence on the surface 

 of the earth, but belong to a creation as distinct 

 as we may suppose that of Venus or Jupiter to 

 be. The data, however, scarcely warrant such a 

 conclusion as this. 



Mr. Charles Darwin has lately alluded to these 

 singular facts in confirmation of his theory of the 

 origin of species by means of natural selection, or 

 the preservation of favoured races in the struggle 

 for life. He takes the first-named view, that in 

 the subterranean animals the organs of sight have 

 become (more or less completely) absorbed, in 

 successive generations, by disuse of the function. 

 "In some of the crabs the foot-stalk remains, 

 though the eye is gone ; the stand for the telescope 

 is there, though the telescope with its glasses has 

 been lost. As it is difficult to imagine that eyes, 

 though useless, could be in any way injurious to 

 animals living in darkness, I attribute their loss 

 wholly to disuse. In one of the blind animals, 

 namely, the cave-rat, the eyes are of immense 

 size; and Professor Silliman thought that it re- 

 gained, after living some days in the light, some 

 slight power of vision. In the same manner as, 

 in Madeira, the wings of some of the insects have 

 been enlarged, and the wings of others have been 

 reduced, by natural selection aided by use and 

 disuse, so in the case of the cave-rat, natural selec- 

 tion seems to have struggled with the loss of light 

 and to have increased the size of the eyes ; where- 

 as, with all the other inhabitants of the caves, 

 disuse by itself seems to have done its work. 



". . . . On my view, we must suppose that 



American animals, having ordinary powers of 



vision, slowly migrated by successive generations 



from the outer world into the deeper and deeper 



6 81 



