part of Sumatra extended eastward and formed the narrow
straits of Banca, many birds and insects and some Mammalia would
cross from one to the other, and thus produce a general similarity of
productions, while a few of the older inhabitants remained, to reveal
by their distinct forms, their different origin. Unless we suppose some
such changes in physical geography to have occurred, the presence of
peculiar species of birds and mammals in such an island as Banca is a
hopeless puzzle; and I think I have shown that the changes required are
by no means so improbable as a mere glance at the map would lead us to
suppose.

For our next example let us take the great islands of Sumatra and Java.
These approach so closely together, and the chain of volcanoes that runs
through them gives such an air of unity to the two, that the idea of
their having been recently dissevered is immediately suggested. The
natives of Java, however, go further than this; for they actually have a
tradition of the catastrophe which broke them asunder, and fix its date
at not much more than a thousand years ago. It becomes interesting,
therefore, to see what support is given to this view by the comparison
of their animal productions.

The Mammalia have not been collected with sufficient completeness in
both islands to make a general comparison of much value, and so many
species have been obtained only as live specimens in captivity, that
their locality has often been erroneously given, the island in which
they were obtained being substituted for that from which they originally
came. Taking into consideration only those whose distribution is more
accurately known, we learn that Sumatra is, in a zoological sense, more
neatly related to Borneo than it is to Java. The great man-like apes,
the elephant, the tapir, and the Malay bear, are all common to the two
former countries, while they are absent from the latter. Of the three
long-tailed monkeys (Semnopithecus) inhabiting Sumatra, one extends into
Borneo, but the two species of Java are both peculiar to it. So also
the great Malay deer (Rusa equina), and the small Tragulus kanchil, are
common to Sumatra and Borneo, but do not extend into Java, where they
are replaced by Tragulas javanicus. The tiger, it is true, is found in
Sumatra and Java, but not in Borneo. But as this animal is known to swim
well, it may have found its way across the Straits of Sunda, or it may
have inhabited Java before it was separa