1 84 THE DOCTRINE OF DESCENT. 



sages only partially obscure, possess less atrophied optic 

 apparatus. A singular gradation occurs among the 

 burrowing mammals, and Darwin ^^ cites an example 

 admirably illustrating the loss of sight in consequence 

 of the mode of life. " In South America a burrowing 

 rodent, the Tuco-tuco, or Ctenomys, is even more 

 subterranean in its habits than the mole ; and I was 

 assured by a Spaniard, who had often caught them, that 

 they were frequently blind ; one which I kept alive was 

 certainly in this condition, the cause, as appeared on 

 dissection, having been the inflammation of the nicti- 

 lating membrane. As frequent inflammation of the 

 eyes must be injurious to any animal, and as eyes are 

 certainly not necessary to animals having subterranean 

 habits, a reduction in their size, with the adhesion of the 

 eyelids and growth of fur over them, might in such case 

 be an advantage ;* and, if so, natural selection would 

 constantly aid the effects of disuse " 



In the classes of flying animals, a large number have 

 left off flying ; and we find their flying apparatus in an 

 aborted or incomplete condition, which perverse judg- 

 ment and reasoning alone can regard as a state of 

 progressive development from yet simpler rudiments. 

 If throughout the great family of the Coleoptera, genera 

 and species are to be found with imperfect flying appa- 

 ratus, consolidated wing covers, &c., if the whole family 

 of Staphylinae does not possess the power of flight, no 

 one dreams of considering them as arrested forms; 

 but it is conceivable that the mode of life in which 

 they differ from the other members of their order and 

 class, gradually superinduced in their flying ancestry the 

 habit of not flying, and at the same time the atrophy 



