play ; while the vicinity of Lombock to Bali and Java
has allowed a continual influx of fresh individuals which,
by crossing with the earlier immigrants, has checked
variation.
To simplify our view of the derivative origin of the
birds of these islands let us treat them as a whole, and
thus perhaps render more intelligible their respective relations
to Java and Australia.
The Timor group of islands contains :—
J avan birds . . .
Closely allied species
Derived from Java
36
11
47
Australian birds . . . 13
Closely allied species . . 35
Derived from Australia ' . 48
We have here a wonderful agreement in the number of
birds belonging to Australian and Javanese groups, but
they are divided in exactly a reverse manner, three-fourths
of the Javan birds being identical species and one-fourth
representatives, while only one-fourth of the Australian
forms are identical and three-fourths representatives. This
is the most important fact which we can elicit from a
study of the birds of these islands, since it gives us a very
complete clue to much of their past history.
Change of species is a slow process. On that we are all
agreed, though we may differ about how it has taken place.
The fact that the Australian species in these islands have
mostly'changed, while the Javan species have almost all
remained unchanged, would therefore indicate that the
district was first peopled from Australia. But, for this to
have been the case, the physical conditions must have been
very different from what they are now. Nearly three
hundred miles of open sea now separate Australia from
Timor, which island is connected with Java by a chain ot
broken land divided by straits which are nowhere more
than about twenty miles wide. Evidently there are now
oreat facilities for the natural productions of Java to Os
pread over and occupy the whole of these islands, while
those of Australia would find very great difficulty in
Oo, ettin°O' across. To account for the present state of things,
we should naturally suppose that Australia was once much
more closely connected with Timor than it is at present;
and that this was the case is rendered highly probable by
the fact of a submarine bank extending along all the north
and west coast of Australia, and at one place approaching
within twenty miles of the coast of Timor. This indicates
a recent subsidence of North Australia, which probably
once extended as far as the edge of this bank, between
which and Timor there is an unfathomed depth of ocean.
I do not think that Timor was ever actually connected
with Australia, because such a large number of very abundant
and characteristic, groups of Australian birds are
quite absent, and not a single Australian mammal has
entered Timor ; which would certainly not have been the
y 2