cteristic groups as
those of Priamus, Ulysses, and Erechtheus are strictly limited to the
Australian region of the archipelago, while five other groups are with
equal strictness confined to the Indian region, is a strong
corroboration of that division which has been founded almost entirely on
the distribution of Mammalia and Birds.

If the various Malayan islands have undergone recent changes of level,
and if any of them have been more closely united within the period of
existing species than they are now, we may expect to find indications of
such changes in community of species between islands now widely
separated; while those islands which have long remained isolated would
have had time to acquire peculiar forms by a slow and natural process of
modification.

An examination of the relations of the species of the adjacent islands,
will thus enable us to correct opinions formed from a mere consideration
of their relative positions. For example, looking at a map of the
archipelago, it is almost impossible to avoid the idea that Java and
Sumatra have been recently united; their present proximity is so great,
and they have such an obvious resemblance in their volcanic structure.
Yet there can be little doubt that this opinion is erroneous, and that
Sumatra has had a more recent and more intimate connexion with Borneo
than it has had with Java. This is strikingly shown by the mammals of
these islands--very few of the species of Java and Sumatra being
identical, while a considerable number are common to Sumatra and Borneo.
The birds show a somewhat similar relationship; and we shall find that
the distribution of the Papilionidae tells exactly the same tale. Thus:--

Sumatra has 21 species }
Borneo " 30 " } 20 sp. common to both islands;

Sumatra " 21 " }
Java " 28 " } 11 sp. common to both islands;

Borneo " 30 " }
Java " 28 " } 20 sp. common to both islands;

showing that both Sumatra and Java have a much closer relationship to
Borneo than they have to each other--a most singular and interesting
result, when we consider the wide separation of Borneo from them both,
and its very different structure. The evidence furnished by a single
group of insects would have had but little weight on a point of such
magnitude if standing alone; but coming as it does to confirm deductions
drawn from whole classes of the higher animals, it must be admitted to
hav