124 ON THE ORIGIN OF SPECIES 



readily took to flight would oftenest have been blown 

 to sea and thus have been destroyed. 



The insects in Madeira which are not ground-feeders, 

 and which, as the flower-feeding coleoptera and lepi- 

 doptera, must habitually use their wings to gain their 

 subsistence, have, as Mr. Wollaston suspects, their 

 wings not at all reduced, but even enlarged. This is 

 quite compatible with the action of natural selection. 

 For when a new insect first arrived on the island, the 

 tendency of natural selection to enlarge or to reduce 

 the wings, would depend on whether a greater number 

 of individuals were saved by successfully battling with 

 the winds, or by giving up the attempt and rarely or 

 never flying. As with mariners shipwrecked near a 

 coast, it would have been better for the good swimmers 

 if they had been able to swim still further, whereas it 

 would have been better for the bad swimmers if they 

 had not been able to swim at all and had stuck to the 

 wreck. 



The eyes of moles and of some burrowing rodents 

 are rudimentary in size, and in some cases are quite 

 covered up by skin and fur. This state of the eyes is 

 probably due to gradual reduction from disuse, but 

 aided perhaps by natural selection. 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 inflammation of 

 the nictitating membrane. As frequent inflammation 

 of the eyes must be injurious to any animal, and as 

 eyes are certainly not indispensable to animals with 

 subterranean habits, a reduction in their size with 

 the adhesion of the eye-lids 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. 



It is well known that several animals, belonging to 

 the most different classes, which inhabit the caves of 



