But
No Such Uniformity Exists, And The Bats Of Each Island Are
Almost, If Not Quite, As Distinct As The Other Mammals.
For
example, sixteen species are known in Borneo, and of these ten
are found in Java and five in Sumatra, a proportion about the
same as that of the Rodents, which have no direct means of
migration.
We learn from this fact, that the seas which separate
the islands from each other are wide enough to prevent the
passage even of flying animals, and that we must look to the same
causes as having led to the present distribution of both groups.
The only sufficient cause we can imagine is the former connection
of all the islands with the continent, and such a change is in
perfect harmony with what we know of the earth's past history,
and is rendered probable by the remarkable fact that a rise of
only three hundred feet would convert the wide seas that separate
them into an immense winding valley or plain about three hundred
miles wide and twelve hundred long. It may, perhaps, be thought
that birds which possess the power of flight in so pre-eminent a
degree, would not be limited in their range by arms of the sea,
and would thus afford few indications of the former union or
separation of the islands they inhabit. This, however, is not the
case. A very large number of birds appear to be as strictly
limited by watery barriers as are quadrupeds; and as they have
been so much more attentively collected, we have more complete
materials to work upon, and are able to deduce from them still
more definite and satisfactory results.
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