|
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
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
which
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
to animals
subterranean habits, a reduction in their
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
and of Kentucky, are blind. In some of the crabs the foot-stalk for the eye remains, though the eye is
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
|
