special interest, is the greatly increased proportion of Australian forms and
decreased proportion of Indian forms, as we go from west to 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 Lombock. In Flores. In Timor.
Javan 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. [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.] It will be observed that the number of birds that
appear to have entered from Australia is much less 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 Timor. 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 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........ ... 33 23 11
Closely allied to Javan birds.. 1 5 6
Total.............. 34 28 17
Australian birds......... 4 5 10
Closely allied to Australian birds 3 9 26
Total..... ......... 7 14 36We 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 to have full play; while the vicinity of Lombock to