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 similarity in their
organisation and affinities might have been expected. This is certainly
not the case if we look at the two whole faunas; with respect to the
insects alone, Schiodte has remarked: "We are accordingly prevented from
considering the entire phenomenon in any other light than something purely
local, and the similarity which is exhibited in a few forms between the
Mammoth Cave (in Kentucky) and the caves in Carniola, otherwise than as a
very plain expression of that analogy which subsists generally between the
fauna of Europe and of North America.
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