ARCTIC ZOOGEOGRAPHY 1 57 



to look into some of the more important recent theories especially as 

 they bear on the present fauna of the whole polar region. 



It is generally admitted that the true polar land fauna, that is, 

 broadly speaking, the animals inhabiting the circumpolar belt north 

 of the limit of trees, has a rather uniform aspect. In most places 

 we find the polar fox, stoat, polar hare, ptarmigans, lemmings, 

 snow buntings, polar bears, seals, walrus, reindeer, some auks, gulls, 

 and waders, and — not to be forgotten — the mosquitoes. We might 

 even with some propriety include in this category a fish, viz. the char, 

 or brook trout {Salvelinus). Others are more local at present, such as 

 the musk ox, certain ducks and geese; and here we might with equal 

 propriety include another fish, the Alaska blackfish {Dallia pec- 

 toralis). Looking more closely into details, however, we find that 

 there are certain inequalities in the distribution of these animals which 

 require explanation. Thus in Spitsbergen we miss certain strictly 

 Arctic vertebrates which in other localities we are used to associate 

 with polar conditions, such as the hare, the lemming, the stoat, while 

 a reindeer and a ptarmigan are abundant. Then again we notice 

 that certain kinds of animals are represented in different parts of the 

 region by- somewhat different, though evidently quite closely related, 

 species. Thus the walrus on the Pacific side {Odobenus divergens) has 

 been separated by zoologists from the one on the Atlantic side (0. 

 rosmarus); the Spitsbergen reindeer and ptarmigan are plainly 

 different from the Greenland species. Moreover, the reindeer and 

 the ptarmigans inhabiting the Arctic portions of Siberia and North 

 America have recently been split up by specialists into a large number 

 of forms or subspecies. Even the polar foxes and the polar bears, 

 though apparently less confined to definite localities, have been 

 similarly subdivided. 



Plainly, the problem of the north pole as a center of origin is entirely 

 different from that of the north pole as a center of distribution. Prob- 

 ably no zoologist' in this generation is naive enough to hold that the 

 typical Arctic animals are indigenous to the polar central area. Every 

 one of the inhabitants of the frozen zone is closely allied to some 

 species originated in or still living in the adjacent southern regions. 

 Even the polar bear, which most zoological taxonomists recognize as 

 the type of a separate genus (Thalarctos) distinct from that of the 

 brown bears {Ursus), possesses no characters different enough to 

 obscure its close relationship to them. The difference is most pro- 

 nounced in the dentition, inasmuch as "the cheek-teeth are relatively 

 small" while "the incisors and canines are enlarged and unusually 

 prehensive in character" as compared with the ordinary bears of 

 the boreal zone. It is easily seen that this modification of the teeth is 

 an adaptation to the peculiar necessities of the feeding habits of the 

 polar bear. The white color may be due to a similar adaptation. 



