34 THE TUNDRA AND ITS FAUNA 
upon cuttlesand crustaceans. The white whale (Delphin- 
apterus leucas) is similarly an Arctic form, remarkable 
for its habit of ascending rivers for a considerable 
distance. The killer whale (Orca gladiator), on the 
other hand, which is a very widely distributed animal, 
chiefly occurs in the Arctic in summer. 
If we sum up the facts in regard to the distribution 
of tundra animals, and of the marine forms which 
occur round its seaward margin, we may say briefly 
that the tundra fauna is virtually uniform throughout. 
The animals, generally speaking, are either circumpolar 
at the present time, or have once been circumpolar, 
and there is no distinction between eastern and western 
faunas. In other words, the fact that the ‘ salt, estrang- 
ing sea’ is here more or less ice-bound makes the land 
areas virtually continuous, and this, combined with the 
marked uniformity of physical conditions, leads to 
practical uniformity of distribution, both of plants and 
of animals. No such similar uniformity exists in regard 
to the other natural regions of the world. Though the 
steppes of Asia show a general resemblance in physical 
conditions to the steppe-like regions of North America, 
yet their faunas are different. In the same way, the 
faunas of the similar equatorial forests of South America 
and Africa are markedly dissimilar, and there is almost 
no resemblance between the desert fauna of Australia 
and those of Africa or of America. No resemblance, 
that is, when the actual affinities of the animals are 
considered, but necessarily desert animals or forest 
animals, whatever their affinities, share certain adapta- 
tions to forest or desert life. 
RerFerences. Accounts of tundra animals are to be found in almost 
all books dealing with the Arctic regions. The following may be men— 
tioned as giving a considerable amount of detail: Manual of the Natural 
