32 THE TUNDRA AND iTS FAUNA 



emphasized — the poverty of the land and the relative 

 wealth of the sea in these northern latitudes. Another 

 cause of the abundance of the seals and their allies in 

 Arctic and Antarctic waters is certainly to be sought 

 in the fact that these animals must come on shore to 

 breed, and suitable regions for this purpose, offering 

 security against attack, except in the case of man, the 

 great enemy of the large mammals, are to be found in 

 the frigid rather than in the temperate or torrid zones. 



Of the Arctic seal-like animals, the walrus (Trichechus 

 rosmarus), which is circumpolar, is one of the most 

 interesting forms. As already noted, it is stated to 

 feed chiefly upon molluscs, but apparently adds fish, 

 swimming birds, and even seals to these. It seems to 

 pass a considerable part of its life on shore, or at least 

 on floating ice-floes. The massive tusks are used in 

 digging up mussels from the mud, and also in helping 

 the animal to clamber upon the ice. 



The true seals are represented by a number of species, 

 five or six occurring in Greenland. The presence of 

 a number of nearly related forms within a limited area 

 means a very perfect adaptation to the natural con- 

 ditions. Analogous conditions are presented by the 

 many kinds of antelope which are found in the open 

 plains of Africa, and the many kinds of deer in the 

 forests of Asia. 



The true seals are very clumsy on land, but are very 

 perfectly adapted for swift movement in the sea. They 

 feed upon fish, to which at times they add shell-fish and 

 crustaceans. In the sea their great enemy is the killer 

 whale, but their enemies on land are much more serious, 

 consisting of the polar bear and man, both of whom 

 take advantage of the animal's relative helplessness on 

 land, and the fact that they must come on shore to 



