five hoofed animals, including the Tapir, two species of rhinoceros, and an
elephant. Besides these there are thirteen Rodents and four Insectivora, including
a shrew-mouse and six squirrels, whose unaided passage over twenty miles of
sea is even more inconceivable than that of the larger animals.
But when we come to the cases of the same species inhabiting two of the more
widely separated islands, the difficulty is much increased. Borneo is distant
nearly 150 miles from Biliton, which is about fifty miles from Banca, and this
fifteen from Sumatra, yet there are no less than thirty-six species of mammals
common to Borneo and Sumatra. Java again is more than 250 miles from
Borneo, yet these two islands have twenty-two species in common, including
monkeys, lemurs, wild oxen, squirrels and shrews. These facts seem to render it
absolutely certain that there has been at some former period a connection
between all these islands and the mainland, and the fact that most of the animals
common to two or more of then, show little or no variation, but are often
absolutely identical, indicates that the separation must have been recent in a
geological sense; that is, not earlier than the Newer Pliocene epoch, at which
time land animals began to assimilate closely with those now existing.
Even the bats furnish an additional argument, if one were needed, to show that
the islands could not have been peopled from each other and from the continent
without some former connection. For if such had been the mode of stocking
them with animals, it is quite certain that creatures which can fly long distances
would be the first to spread from island to island, and thus produce an almost
perfect uniformity of species over the whole region. 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