THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 145 



most other groups of animals. It is true that we shall find a 

 great many unsolved problems, upon which the most divergent 

 opinions are held, but the main outlines of the scheme are quite 

 generally agreed upon. 



Many plans for the zoological division of the continental 

 areas have been proposed by various writers on the subject, 

 some differing very radically from others. It would be useless 

 and tedious to review even the more important of the many 

 proposals and suggestions which have been made in the last 

 half-century ; and we may, with advantage, adopt an eclectic 

 scheme which has been slowly reached by successive approx- 

 imations to a satisfactory arrangement. 



Just as in political geography it is found necessary to rec- 

 ognize divisions of different rank and scope, like nation, state, 

 county, township, the facts of zoological geography require 

 divisions of diflFerent orders of importance. Thus, in descend- 

 ing order, the terms realm, region, subregion, province, etc. 

 are commonly employed, but unfortunately they are often 

 used loosely and even interchangeably ; yet it is desirable to 

 attach a more or less precise significance to each and more 

 terms are needed for an accurate expression of the many 

 complex facts. 



The extreme zoological peculiarity of AustraUa is recognized 

 by making that continent and its adjoining islands one of the 

 great primary divisions, of which the other includes all the 

 rest of the world ; the former is characterized by its almost 

 exclusively marsupial fauna, while the other continents are 

 inhabited by the Monodelphia or placental mammals. Aside 

 from Australia, by far the most isolated and peculiar region 

 of the earth is South America, and this fact is expressed by 

 constituting it into a realm, or division of the second order, and 

 to this realm is given the name Neogcea. The remaining con- 

 tinents. North America, Europe, Asia and Africa, make up 

 the other realm, Arctogcea, in which there is an unmistakable 

 general likeness among the mammals. The three continents 



