360 
ISLAND LIFE. 
[part II. 
species of birds and mammals may have been driven south- 
ward, and ranged over suitable portions of the whole area. 
Java Was then separated by subsidence, and these species 
became imprisoned there ; while those in the remaining part of 
the Malayan area again migrated northward when the cold had 
passed away from their former home, the equatorial forests of 
Borneo, Sumatra, and the Malay Peninsula being more especially 
adapted to the typical Malayan fauna which is there developed 
in rich profusion. A little later the subsidence may have 
extended farther north, isolating Borneo and Sumatra, but pro- 
bably leaving the Malay Peninsula as a ridge between them as 
far as the islands of Banca and Biliton. Other slight changes 
of climate followed, when a further subsidence separated these 
last-named islands from the Malay Peninsula, and left them 
with two or three species which have since become slightly 
modified. We may thus explain how it is that a species is 
sometimes common to Sumatra and Borneo, while the inter- 
vening island (Banca) possesses a distinct form. 1 
In my Geographical Distribution of Animals, Yol. I., p. 357, I 
have given a somewhat different hypothetical explanation of the 
relations of Java and Borneo to the continent, in which I took 
account of changes of land and sea only ; but a fuller consideration 
of the influence of changes of climate on the migration of animals, 
has led me to the much simpler, and, I think, more probable, 
explanation above given. The amount of the relationship be- 
tween Java and Siam, as well as of that between Java and the 
Himalayas, is too small to be well accounted for by an indepen- 
dent geographical connection in which Borneo and Sumatra did 
not take part. It is, at the same time, too distinct and indisput- 
able to be ignored ; and a change of climate which should drive 
a portion of the Himalayan fauna southward, leaving a few 
species in Java, from which they could not return owing to 
its subsequent isolation by subsidence, seems to be a cause 
exactly adapted to produce the kind and amount of affinity 
between these distant countries that actually exists. 
1 Pitta megarhynchus (Banca) allied to P. brachyurus (Borneo, Suma- 
tra, Malacca) ; and Pitta bangJcanus (Banca) allied to P. sordid us (Borneo 
and Sumatra). 
