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." On my view
we must suppose that American animals, having in most cases ordinary
powers of vision, slowly migrated by successive generations from the
outer world into the deeper and deeper recesses of the Kentucky caves,
as did European animals into the caves of Europe. We have some evidence
of this gradation of habit; for, as Schiodte remarks: "We accordingly
look upon the subterranean faunas as small ramifications which have
penetrated into the earth from the geographically limited faunas of the
adjacent tracts, and which, as they extended themselves into darkness,
have been accommodated to surrounding circumstances. Animals not
far remote from ordinary forms, prepare the transition from light to
darkness. Next follow those that are constructed for twilight; and, last
of all, those destined for total darkness, and whose formation is quite
peculiar." These remarks of Schiodte's it should be understood, apply
not to the same, but to distinct species. By the time that an animal had
reached, after numberless generations, the deepest recesses, disuse
will on this view have more or less perfectly obliterated its eyes, and
natural selection will often have effected other changes, such as an
increase in the length of the antennae or palpi, as a compensation for
blindness. Notwithstanding such modifications, we might expect still to
see in the cave-animals of America, affinities to the other inhabitants
of that continent, and in those of Europe to the inhabitants of the
European continent. And this is the case with some of the American
cave-animals, as I hear from Professor Dana; and some of the European
cave-insects are very closely allied to those of the surrounding
country. It would be difficult to give any rational explanation of the
affinities of the blind cave-animals to the other inhabitants of the
two continents on the ordinary view of their independent creation.