THE DISTRIBUTION OF ANIMALS. 
375 
currents. The heavy aquatic Mammals, as Whales, Wal¬ 
ruses, Seals, and Porpoises, are mainly polar. 
The land consists of the following somewhat distinct 
areas: the Neotropic, comprising South America, the West 
Indies, and most of Mexico; the Nearctic, including the 
rest of America; the Palaearctic, composed of the eastern 
continent north of the Tropic of Cancer, and the Hima¬ 
layas ; the Ethiopian, or Africa south of the Tropic of 
Cancer; the Oriental, or India, the southern part of Chi¬ 
na, the Malay Peninsula, and the islands as far east as 
Java, Borneo, and the Philippine Islands; and the Aus¬ 
tralian, or the eastern half of the Malay Islands and Aus¬ 
tralia. These are Mr. Wallace’s regions. Other writers 
unite the northern parts of both hemispheres into one 
.region, and the Oriental with the Ethiopian regions. 
Life in the polar regions is characterized by great uni¬ 
formity, the species being few in number, though the 
number of individuals is immense. The same animals in¬ 
habit the arctic portions of the three continents; while the 
antarctic ends of the continents, Australia, Cape of Good 
Hope, and Cape Horn, exhibit strong contrasts. Those 
three continental peninsulas are, zoologically, separate 
worlds. In fact, the whole southern hemisphere is pecul¬ 
iar. Its fauna is antique. Australia possesses a strange 
mixture of the old and new. South America, with newer 
Mammals, has older Reptiles; while Africa has a rich 
vertebrate life, with a striking uniformity in its distribu¬ 
tion. Groups, old geologically and now nearly extinct, 
are apt to have a peculiar distribution ; as the Edentata in 
South America, Africa, and India; the Marsupials in Aus¬ 
tralia and America; the Ratitse in South America, Africa, 
Australia, and New Zealand. 
In the tropics, diversity is the law. Life is more varied 
and crowded than elsewhere, and attains its highest devel¬ 
opment. 
