CHAPTER XIV. 



DISTRIBUTION IN SPACE. 



Under the general term of "Distribution" come all^the 

 facts concerning the external or objective relations of ani- 

 mals — that is to say, their relations to the external conditions 

 by which they are surrounded. 



The geographical distribution of animals is concerned with 

 the determination of the areas within which every species of 

 animal is at the present day confined. Some species are 

 found almost everywhere, when they are said to be " cos- 

 mopolitan ; " but, as a rule, each species is confined to a 

 limited and definite area. Not only are species limited in 

 their distribution, but it is possible to divide the earth's sur- 

 face into a certain number of geographical regions or " zoo- 

 logical provinces," each of which is characterised by the 

 occurrence in it of certain associated forms of animal life. 

 The number of these provinces has not yet been universally 

 agreed upon, and it is unnecessary here to enter into this 

 subject in detail. There are, however, some general con- 

 siderations which may be briefly alluded to. 



The geographical distribution of land animals is condi- 

 tioned partly by the existence of suitable surroundings, and 

 partly by the presence of barriers preventing migrations. 

 Thus, certain contiguous regions might be equally suitable 

 for the existence of the same animals, but they might belong 



