CHAP. II THE ELEMENTARY FACTS OF DISTRIBUTION 27 



We must therefore consider them somewhat more 

 fully. 



Among mammalia the most remarkable of these divided 

 families is that of the camels, of which one genus 

 Camelus, the true camels, comprising the camel and 

 dromedary, is confined to Asia, while the other Auchenia, 

 comprisng the llamas and alpacas, is found only in the 

 high Andes and in the plains of temperate South America. 

 Not only are these two genera separated by the Atlantic 

 and by the greater part of the land of two continents, but one 

 is confined to the Northern and the other to the Southern 

 hemisphere. The next case, though not so well known, is 

 equally remarkable ; it is that of the Centetida?, a family 

 of small insectivorous animals, which are wholly confined 

 to Madagascar and the large West Indian islands Cuba 

 and Hayti, the former containing five genera and the latter 

 a single genus with a species in each island. Here again 

 we have the whole continent of Africa as well as the 

 Atlantic ocean separating allied genera. Two families (or 

 subfamilies) of rat-like animals, Octodontidse and 

 Echimyidse, are also divided by the Atlantic. Both are 

 mainly South American, but the former has two genera in 

 North and East Africa, and the latter also two in South 

 and West 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 EchimyidaB 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 Megala3mida3 or barbets are gaily coloured 



