east. We shall show this in a yet more striking manner
by counting the number of species identical with those of
Java and Australia respectively in each island, thus :
In Lomboclt. In Flores. In Timor.
.Tavan birds . . . 33 23 11
Australian birds . . 4 5 10
Here we see plainly the course of the migration which
has been going on for hundreds or thousands of years, and
is still going on at the present day. Birds entering from
Java are most numerous in the island nearest Java ; each
strait of the sea to be crossed to reach another island offers
an obstacle, and thus a smaller number get over to the
next island.1 It will be observed that the number of
birds that appear to have entered from Australia is much
les.s'than those which have come from Java ; and we may
at first sight suppose that this_ is due to the wide sea that
separates Australia from Timot' But this would be a hasty
and, as we shall soon see, an unwarranted supposition.
Besides these birds identical with species inhabiting Java
and Australia, there are a considerable number of others
very closely allied to species peculiar to those countries,
and we must take these also into account before we form
i The names of all the birds inhabiting these islands are to be found
in the “ Proceedings of the Zoological Society of London” for the year
1863.
any conclusion on the matter. It will be as well to combine
these with the former table thus :
In Lombock. In Flores. In Timor.
Javan birds’ ............................
Closely allied to Javan birds
Total , . •
Australian b i r d s . ......................
Closely allied to Australian birds
Total . . . .
33 23 li
mbs! 5 6
_ — —
34 28 17
—
4 5 10
3 9 26
7 14 36
i H I (—
We now see that the total number of birds which seem
to have been derived from Java and Australia is very
nearly equal, but there is this remarkable difference between
the two series: that whereas the larger proportion
by far of the Java set are identical with those still inhabiting
that country, an almost equally large proportion of the
Australian set are distinct/though often very closely allied
species. It is to be observed also, that these representative
or allied species diminish in number as they recede from
Australia, while they increase in number as they recede
from Java. There are two reasons for this, one being that
the islands decrease rapidly in size from Timor to Lombock,
and can therefore support a decreasing number of
species; the other and the more important is, that the distance
of Australia from Timor cuts off the supply of fresh
immigrants, and has thus allowed variation O 7 to have full
VOL. I. Y