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 
Tragulidae 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 Simiidae 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 Echimyidse 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- 
laemidae 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- 
phidse or tree-snakes, and the Dryiophidae 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 Lepidosternidae 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 Phryniscidae. Insects also furnish some analogous 
cases, three genera of Cicindelidae (Pogonostoma, Ctenostoma, 
and Peridexia) showing a decided connection between this 
family in South America and Madagascar ; while the beautiful 
