ALLEN ON GEOGRAPHICAL DISTRIBUTION OF MAMMALS. 331 



of the southern third of South America, a small portion of Southern 

 Africa, and the greater portion of Australia. Extra- tropical South 

 Africa is all comprised within the Warm Temperate Zone, and is so small 

 in area and so intimately related, both geographically and faunally, 

 with Tropical Africa, that its formal separation, while, perhaps, war- 

 ranted in the abstract, is hardly practically necessary. Temperate South 

 America is exceedingly irregular in its northern outline, owing to pecu- 

 liarities of configuration, resulting from the presence of the great Andean 

 Plateau, by means of which it extends along the western border of 

 South America far northward of the southern tropic. Temperate Aus- 

 tralia is clearly separable from the tropical portion of the Australian 

 Realm. The South Temperate Zone hence consists of three compara- 

 tively small land-areas, widely separated from each other, and conse- 

 quently, as would be supposed, have little in common. 



The Antarctic Eegion has a very limited amount of land-surface, and 

 the few species that compose its fauna are almost wholly either marine 

 or pelagic. As previously stated, as a mammalian region it has little 

 significance. 



This hasty sketch shows that the differentiation of the land-surface 

 of the earth into realms, regions, and minor divisions has relation not 

 only to climate, but to the divergence and isolation of the different 

 principal land-areas ; that at the northward, where the lands converge, 

 there is no partitioning in conformity with continental areas, the tem- 

 perate and colder portions of the northern hemisphere all falling into 

 a single primary division, and that only the southern half is susceptible 

 of divisions of the second rank. Within the tropics, on the other hand, 

 the lands of the eastern and western hemispheres fall at once into dif- 

 ferent primary regions, and one of these is again divisible into regions 

 of second rank. Beyond the tropics, the land-surfaces are of small ex- 

 tent, widely separated, and faunally have almost nothing in common. 



With these preliminary remarks, we may now pass to a detailed con- 

 sideration of the several primary regions and their subdivisions. 



I. ARCTIC REALM. 



Whether or not an Arctic Region should be recognized as a division 

 of the first rank is a question not easy to satisfactorily answer. Natur- 

 alists who have made the distribution of animal life in the boreal 

 regions a subject of special study very generally agree in the recogni- 

 tion of a hyperboreal or circumpolar fauna, extending in some cases far 

 southward over the Temperate Zone. The Arctic portion of this hyper- 

 borean region has been frequently set off as a secondary division, or 

 subregion,* and generally recognized as possessing many features not 



*It forms Mr. Blyth's "Arctic Subregion" (Nature, vol. iii,p. 427, March 30, 1871), 

 Mr. Brown's " Circumpolar" division (Proc. Zool. Soc., Lond., 1868, p. 337), and Dr. 

 von Middendorfi's " Zirkumpolar-Fauna" (Sibirische Reise, Bd. iv, p. 910,1867). It 

 also accords very nearly with Agassiz's "Arctic Realm " (Nott and Gliddon's Types 

 of Mankind, 1854, p. Ix and map). 



