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 Ratitae 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. 



