chap, xii.] THE ORIENTAL REGION. 353 



these higher animals become replaced by allied species much 

 more rapidly than the mollusca; and it is also pretty certain 

 that the modification by which this replacement is effected 

 takes place more rapidly when the two sets of individuals are 

 isolated from each other, and especially when they are restricted 

 to islands, where they are necessarily subject to distinct and 

 pretty constant conditions, both physical and organic. It 

 becomes therefore almost a certainty, that Siam and Java on 

 the one hand, and Sumatra, Borneo, and Malacca on the other 

 must have been brought into some close connexion, not earlier 

 than the newer Pliocene period ; but while the one set of 

 countries were having their meeting, the other must have been 

 by some means got out of the way. Before attempting to 

 indicate the mode by which this might have been effected in 

 accordance with what we know of the physical geography, 

 geology, and vegetation of the several islands, it will be as well 

 to complete our sketch of their zoological relations to each 

 other, so as ascertain with some precision, what are the facts 

 of distribution which we have to explain. 



Malacca, Sumatra, and Borneo. — After having set apart the 

 Philippine Islands and Java, we have remaining two great 

 islands and a peninsula, which, though separated by con- 

 siderable arms of the sea, possess a fauna of wonderful uni- 

 formity having all the typical Malayan features in their full 

 development. , Their unity is indeed so complete, that we can 

 find hardly any groups of sufficient importance by which to 

 differentiate them from each other ; and we feel no confidence 

 that future discoveries may not take away what speciality they 

 possess. One after another, species or genera once peculiar to 

 Borneo or Sumatra have been found elsewhere; and this has 

 gone to such an extent in birds, that hardly a peculiar genus 

 and very few peculiar species are left in either island. Borneo 

 however is undoubtedly the most peculiar. It possesses three 

 genera of Mammalia not found elsewhere : Cynogale, a curious 

 carnivore allied to the otters ; with Dendrogale and Ptilocerus, 

 small insectivora allied to Tupaia. It has Simla, the Orang- 



