It is difficult to imagine conditions of life more similar than deep
limestone caverns under a nearly similar climate; so that on the
common view of the blind animals having been separately created for
the American and European caverns, close similarity in their
organisation and affinities might have been expected; but, as Schiodte
and others have remarked, this is not the case, and the cave-insects
of the two continents are not more closely allied than might have been
anticipated from the general resemblance of the other inhabitants of
North America and Europe. On my view we must suppose that American
animals, having 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, "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." 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.
Pages:
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178