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 fa.rther 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.^ 



In my GeograjMcal 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, 

 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 Fitta megarhynchus (Banca) allied to P. brachyurus (Borneo, Suma- 

 tra, Malacca) ; and Pitta banglcanus (Banca) allied to P. sordidus (Borneo 

 and Sumatra). 



