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 (T'richechus 
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 
