EFFECTS OF USE Nl) DISUSE. 128 



The insects in Madeira which are not ground-feeders, and 

 which, as certain flower-feeding coleoptera and lepidoptera, 

 must habitually use their wings to gK.n 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 tei. .ency 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 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 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 cer- 

 tainly 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 aid the effects 

 of disuse. 



It is well known that several animals, belonging to the 

 most different classes, which inhabit the caves of Carniola 

 and Kentucky, are blind. In some of the crabs Jae foot- 

 stalk for the eyes 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, their loss may be attributed to 

 disuse. In one of the blind animals, namely, the cave- 

 rat (Neotoma), two of which were captured by Professor 

 Silliman at above half a mile distance from the mouth of 

 the cave, and therefore not in the profoundest depths, the 



