s 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 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
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 the foot-stalk for the eye 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 eyes were
lustrous and of large size; and these animals, as I am informed by
Professor Silliman, after having been exposed for about a month to a
graduated light, acquired a dim perception of objects.

It is difficult to imagine conditions of life more similar than deep
limestone caverns under a nearly similar climate; so that, in accordance
with the old view of the blind animals having been separately created
for the American and European caverns, very close