I.] DISTRIBUTIONAL AREAS. 19 



is a term to the life of an individual, what is more natural than 

 that there should also be one to the existence of a species ? It still 

 remains, indeed, to account for the fact that the larger Plistocene 

 mammals had no successors in the greater part of the world, but 

 perhaps this is in some way connected with the advent of man. 



Before coming to the consideration of the zoological divisions 

 into which, from the present geographical distribu- 

 tion of mammals, the world may be mapped out, it tionai Areas of 

 is necessary to devote a brief space to the considera- Genera^ and 

 tion of two other points ; the first relating to the 

 relative size of the distributional area of genera and species, and 

 the second to the permanency of ocean-basins and continents. 



As regards the first point, it appears to be true in the case of 

 mammals (although not of all other groups) that every species has 

 a continuous distributional area, except where this has been broken 

 up by human destructiveness. It is not meant by this that every 

 part of such area is inhabited by the particular species, as 

 "station" renders this impracticable; but merely that the whole 

 area is ranged over by the species in such spots as are suited to 

 its particular mode of life. Great variation obtains, however, in 

 regard to the size of such distributional area; and it will be 

 obvious that the size of the area varies directly as the adaptability 

 of the species to different climatic and other physical conditions. 

 Perhaps the most important condition of all is the possibility of 

 obtaining suitable food ; and in this respect carnivorous mammals 

 are in a far better position than any other members of their class, 

 since the kind of animal on which they prey is immaterial. This 

 will readily account for the extensive geographical ranges enjoyed 

 by the puma and the tiger, which, as stated on page 5, embrace 

 almost every degree of latitude. Animals with such a wide dis- 

 tribution are of but little use to the student of geographical 

 distribution. Moreover, it will generally be found that species 

 with a wide range belong to large genera having a still more 

 extensive distributional area; this being markedly the case with 

 the puma and the tiger ; the genus Felts being one of the largest 

 in the class, and ranging over the whole world with the exception 

 of Australasia. Such cosmopolitan genera are likewise almost 

 valueless to the distributionist. 



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