chap, i.] PHYSICAL GEOGRAPHY. 19 



species are exactly identical. Birds offer us one of the 

 best means of determining the law of distribution ; for 

 though at first sight it would appear that the watery 

 boundaries which keep out the land quadrupeds could be 

 easily passed over by birds, yet practically it is not so ; 

 for if we leave out the aquatic tribes which are pre- 

 eminently wanderers, it is found that the others (and 

 especially the Passeres, or true perching-birds, which form 

 the vast majority) are generally as strictly limited by 

 straits and arms of the sea as are quadrupeds themselves. 

 As an instance, among the islands of which I am now 

 speaking, it is a remarkable fact that Java possesses 

 numerous birds which never pass over to Sumatra, though 

 they are separated by a strait only fifteen miles wide, and 

 with islands in mid-channel. Java, in fact, possesses more 

 birds and insects peculiar to itself than either Sumatra 

 or Borneo, and this would indicate that it was earliest 

 separated from the continent ; next in organic indivi- 

 duality is Borneo, while Sumatra is so nearly identical 

 in all its animal forms with the peninsula of Malacca, 

 that we may safely conclude it to have been the most 

 recently dismembered island. 



The general result therefore at which we arrive is, that 

 the great islands of Java, Sumatra, and Borneo resemble 

 in their natural productions the adjacent parts of the 

 continent, almost as much as such widely-separated 



c2 



