8 PHILOSOPHY OF ZOOLOGY. 



CHAP. 11. 



ON THE DISTRIBUTION OF ANIMALS. 



J.N examining the zoological productions of different coun- 

 tries, we observe, that the species which are commonly met 

 with in one district, are rare, or not to be detected, in the 

 others. If we confine our attention to any one species, we 

 shall observe, that there is some particular country where 

 the individuals are most numerous, and where the energies 

 of life are exerted with the greatest activity. iVs we recede 

 from this district, the individuals become less numerous, 

 their increase goes on at a slower rate, and those which axe 

 produced are rather of dwarfish stature : at length, we reach 

 the limits beyond which they do not extend. The geogra- 

 phical distribution of each species, therefore, may be re- 

 presented by a circle, towards the centre of which, existence 

 can be comfortably maintained ; but as we approach the cir- 

 cumference, restraints multiply, and life at last becomes im- 

 practicable. Each species has a range peculiar to itself, so 

 that the circles of different species intersect one another in 

 every possible relation. 



The extent of the earth's surface over which the indivi- 

 duals of a species are dispersed, can only be ascertained af- 

 ter a long series of observations, conducted by naturalists 

 in different countries. Hitherto the geographical limits of 

 but few species have been satisfactorily determined. These 

 chiefly belong to the larger species of quadrupeds, as the 

 African and Asiatic elephants, the ass and the quagga, the 

 lion, hippopotamus, and polar bear. In the tribes of the 

 less perfect animals, the species of which have been investi- 

 gated by few, the extent of their GEOGUArmcAL Distui- 

 BUTioN has been very imperfectly determined. 



