385 ISLAND LIFE part ii 



severest part of which a few Himalayan species of birds 

 and mammals may have been driven southward, and 

 have ranged over suitable portions of the whole area. Java 

 then became separated by subsidence, and these species were 

 imprisoned in the island ; 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, in which a few other 

 Indian or Indo-Chinese forms have been retained, but prob- 

 ably 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 subsi- 

 dence 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 intervening island (Banca) 

 possesses a distinct form.^ 



In my Oeographical Distribution of Animals, Vol. 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, explan- 

 ation above given. The amount of the relationship 

 between Java and Siam, as well as that between Java 

 and the Himalayas, is too small to be well accounted for 

 by an independent geographical connection in which 

 Borneo and Sumatra did not take part. It is at the same 

 time too distinct and indisputable to be ignored; and a 

 change of climate which should drive a portion of the 

 Himalayan fauna southward, leaving a few species in Java 



1 Pitta megarhijncJms (Biincei) allied to P. hrachyicrus (Borneo, Sumatra, 

 Malacca) ; and Pitta hangkaiius (Banca) allied to P. sordidus (Borneo and 

 Sumatra). 



