CHAP. II.] THE ELEMENTARY FACTS OF DISTRIBUTION. 



27 



Africa. Two other families of mammalia, though confined to 

 the Eastern hemisphere, are yet markedly discontinuous. The 

 Tragulidse are small deer-like animals, known as chevrotains or 

 mouse- deer, abundant in India and the larger Malay islands 

 and forming the genus Tragulus ; while another genus, 

 Hyomoschus, is confined to West Africa. The other family is 

 the Simiida^ or anthropoid apes, in which we have the gorilla 

 and chimpanzee confined to West and Central Africa, while 

 the allied orangs are found only in the islands of Sumatra 

 and Borneo, the two groups being separated by a greater 

 space than the Echimyida3 and other rodents of Africa and 

 South America. 



Among birds and reptiles we have several families, which, 

 from being found only within the tropics of Asia, Africa, and 

 America, have been termed tropicopolitan groups. The Mega- 

 Isemidse or barbets are gaily coloured fruit-eating birds, almost 

 equally abundant in tropical Asia and Africa, but less plentiful 

 in America, where they probably suffer from the competition of 

 the larger sized toucans. The genera of each country are 

 distinct, but all are closely allied, the family being a very 

 natural one. The trogons form a family of very gorgeously 

 coloured and remarkable insect-eating birds very abundant in 

 tropical America, less so in Asia, and with a single genus of 

 two species in Africa. 



Among reptiles we have two families of snakes — the Dendro- 

 phidae or tree-snakes, and the Dryiophidse or green whip-snakes 

 — which are also found in the three tropical regions of Asia, 

 Africa, and America, but in these cases even some of the genera 

 are common to Asia and Africa, or to Africa and America. The 

 lizards forming the small family Lepidosternidse are divided 

 between tropical Africa and South America, while even the 

 peculiarly American family of the iguanas is represented by 

 two genera in Madagascar. Passing on to the Amphibians the 

 worm-like Caeciliadae are tropicopolitan, as are also the toads of 

 the family Phryniscidse. Insects also furnish some analogous 

 cases, three genera of Cicindelidse (Pogonostoma, Ctenostoma, 

 and Peridexia) showing a decided connection between this 

 family in South America and Madagascar ; while the beautiful 



