10 THE GEOGRAPHY OF MAMMALS 



scarcely any ground for connecting the Neotropical and 

 Australian Regions under one name. 



Before discussing the other differences between this 

 scheme and that of Huxley, it will be as well to mention 

 the diverging views of some other naturalists. Of these 

 the chief is Professor Heilprin, of Philadelphia, who 

 in his "Geographical and Geological Distribution of 

 Animals," (5) " in accordance with a suggestion by Professor 

 Newton," has proposed to unite the Nearctic and Palsearctic 

 Regions into a single realm — the " Holarctic " — and to 

 separate the Pacific Islands from Australia as the " Poly- 

 nesian Realm." Again, Mr. J. A. Allen, of New York, in 

 his recently published essays (1 and 2), has shown con- 

 siderable independence of thought in this matter. In the 

 introduction to the later of them, which deals chiefly with 

 the distribution of North American mammals, Mr. Allen 

 gives an account of the influences which, in his opinion, 

 mainly determine the geographical distribution of life, 

 dwelling first on the great importance of temperature and 

 moisture, and afterwards on the inter-relation of land- 

 areas, which, he says, is " co-eval and perhaps more than 

 co-ordinate with climate in its influence upon the distribu- 

 tion of life." Next, Mr. Allen treats of the seven primary 

 life-regions, or " realms " as he terms them, into which he 

 proposes to divide the Earth. These are : — 



1. An Arctic Realm, occupying all the country in 

 both hemispheres north of the isotherm 32° F., this 

 boundary corresponding very closely to that of the 

 northern limit of trees. 



2. A North Temperate Realm, occupying the whole of 

 the northern hemisphere between the isotherms of 32° 

 and 70° P. 



