190 GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 



America, one species takes the place of another, a third suc- 

 ceeds the second, and so on, until finally the fauna is found 

 to be completely changed, though it is not always possible 

 to mark the precise line which divides the one from the 

 other. 



405. The range of species does not at all depend upon 

 their powers of locomotion ; if it were so, animals which 

 move slowly and with difficulty would have a narrow range, 

 whilst those which are very active would be widely diffused. 

 Precisely the reverse of this is actually the case. The com- 

 mon oyster extends at least from the St. Lawrence to the 

 Carolinas ; its range is consequently very great ; much more 

 so than that of some of the fleet animals, as, for instance, the 

 Moose. It is even probable that the very inability of the 

 oyster to travel really contributes to its diffusion, inasmuch 

 as, having once spread over extensive grounds, there is no 

 chance of its return to a former limitation, inasmuch as, being 

 fixed, and consequently unable to choose positions for its 

 eggs, they must be left to the mercy of currents ; while 

 Fishes, by depositing their eggs in the bays and inlets of the 

 shore, undisturbed by currents and winds, secure them from 

 too wide a dispersion. 



406. The nature of their food has an important bearing 

 upon the grouping of animals, and upon the extent of their 

 distribution. Carnivorous animals are generally less con- 

 fined in their range than herbivorous ones ; because their 

 food is almost every where to be found. The herbivora, on 

 the contrary, are restricted to the more limited regions 

 corresponding to the different zones of vegetation. The 

 same remark may be made with respect to Birds. Birds of 

 prey, such as the eagle and vulture, have a much wider range 

 than the granivorous and gallinaceous birds. Still, notwith- 

 standing the facilities they have for change of place, even 

 the birds that wander widest recognize limits which they do 



