364 COMPARATIVE ZOOLOGY. 
light in lakes and rivers, and Moles are subterranean. As 
of Birds, the aquatic species abound in the polar regions. 
Marsupials inhabit two widely separated areas—America 
and Australia. In the latter continent, they constitute 
three-fourths of the fauna; while Edentates, Ruminants, 
Fig. 351.—Zones of Animal Life. 
Horses, Elephants, Hogs, Squirrels, Moles, Carnivores, 
Monkeys, and Apes are wanting. Excepting a few spe- 
cies in South Africa and South Asia, Edentates are con- 
fined to tropical South America. The equine family is 
indigenous to South and East Africa and Sonthern Asia. 
In North America, Rodents form about one-half the num- 
