222 NATURAL HISTORY OF THE [chap. ix. 



150 miles from Biliton, which is about fifty miles from 

 Banca, and this fifteen from Sumatra, yet there are no 

 less than thirty -six species of mammals common to Borneo 

 and Sumatra. Java again is more than 250 miles from 

 Borneo, yet these two islands have twenty-two species in 

 common, including monkeys, lemurs, wild oxen, squirrels, 

 and shrews. These facts seem to render it absolutely cer- 

 tain that there has been at some former period a connexion 

 between all these islands and the main land, and the fact 

 that most of the animals common to two or more of them 

 show little or no variation, but are often absolutely identi- 

 cal, indicates that the separation must have been recent in 

 a geological sense ; that is, not earlier than the Newer 

 Pliocene epoch, at which time land animals began to 

 assimilate closely with those now existing. 



Even the bats furnish an additional argument, if one 

 were needed, to show that the islands could not have been 

 peopled from each other and from the continent without 

 some former connexion. For if such had been the mode of 

 stocking them with animals, it is quite certain that creatures 

 which can fly long distances would be the first to spread 

 from island to island, and thus produce an almost perfect 

 uniformity of species over the whole region. But no such 

 uniformity exists, and the bats of each island are almost, 

 if not quite, as distinct as the other mammals. For 

 example, sixteen species are known in Borneo, and of 



