20 ANIMAL LIFE AND SOCIAL GROWTH 



to a different order. The okapis, the elephants 

 and the apes of the African forests are absent in 

 South America, while the tapirs of the latter region 

 live in the forests of Malay but are absent from 

 the other tropical forests of the old world. 



The continental differences in ground mammals 

 are fully as marked among arboreal forms. The 

 South American monkeys have prehensile tails, 

 their nostrils open outwards and they lack cheek 

 pouches. The old world monkeys, on the other 

 hand, lack a prehensile tail, they have cheek 

 pouches and their nostrils open downwards close 

 together. The two possess other structural dif- 

 ferences which divide them into two distinct taxo- 

 nomic series. The monkeys of the African and 

 the Asiatic forests are less distinct but they be- 

 long to different families; and the forests of tropi- 

 cal Australia are inhabited by animals such as the 

 tree kangaroos and other marsupials which are not 

 to be found elsewhere. These animals that oc- 

 cupy similar niches in the tropical rain-forests of 

 the world are physiologically equivalent despite 

 their differences in structure and classification. 

 Physiologically they reflect their environment 

 while their anatomy shows that they have arisen 

 from diverse stocks. 



The animals of the northern forest are more 

 similar on both the American and the Eurasian 



