30 THE TUNDRA AND ITS FAUNA 



gives him almost nothing. It is a commonplace of 

 physiology that in cold climates his need of fat is great, 

 but in this respect he resembles all the other animals 

 of the region, all of whom seek fatty food, and store 

 up in their bodies reserves of this heat-producing sub- 

 stance. The food from which the larger marine animals 

 obtain their supplies of fat is almost always, directly or 

 indirectly, found in the myriads of small Crustacea which 

 haunt polar seas, and whose bodies contain much oil. 

 Arctic seas are indeed specially characterized by their 

 wealth of small Crustacea and of marine mammals, and 

 the two facts are closely connected. The Crustacea feed 

 the fish of the polar seas, which, though of relatively 

 few species, are often extraordinarily abundant as 

 individuals. The seals and toothed whales feed upon 

 fish. Small Crustacea are also devoured by molluscs, 

 of which the mud-haunting forms are devoured by the 

 walrus, and the floating forms by the whalebone whales, 

 so that the Crustacea form the basis of the marine food- 

 supply. They are in their turn fed by the more minute 

 forms of life, especially by the minute plants, such as 

 the diatoms, so abundant in polar seas. 



The few survivors of the iU-fated Greely expedition 

 kept themselves alive by the collection of ' shrimps ' 

 in the shore-water. These ' shrimps ' must have been 

 largely the small crustaceans called amphipods, which 

 are enormously abundant in polar seas, and the fact 

 that they were so utilized may be taken as emblematic 

 of Arctic conditions. 



Apart from Crustacea, the littoral fauna of the Arctic 

 is fairly rich. A considerable number of large molluscs 

 occur, including in the ' gapers ' Mya and Saxicava 

 mussel-hke forms, which constitute an important part 

 of the food of the walrus. Where molluscs abound, 



