184 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 Staphylinze 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 
