8 ON THE GEOGRAPHY OF ANIMALS. 



influence on local distribution, but they have nothing to 

 do with the geographic distribution of animals indi- 

 genous to large continents: nor will they even explain 

 the local distribution of some of the commonest birds. 

 It may be said, indeed, that the absence of the night- 

 ingale in Northumberland and Scotland is to be at- 

 tributed to the greater coldness of those parts, compared 

 with the milder air of southern England. But how 

 are we to account for this bird being common in the 

 more northern kingdoms of Sweden and Germany ? 

 Climate, in this case, can have no influence ; neither can 

 food, since insects and their larvae, of the same species, 

 are found in all these localities : the thickets of Scot- 

 land are as favourable for breeding in as those of 

 Sweden ; and in regard to foes, no reason can possibly be 

 devised. In what way, also, can the circular range of the 

 nigli.'ngale be made out.'' Again, we will allow that 

 these causes are sufficient to account for the fire -crested 

 warbler (^Sylvia ignicapilla) being found in the Parisian 

 gardens, while it is a stranger to England. The dif- 

 ference of temperature, we will say, is the reason : 

 England is colder than France. But how are we to 

 account for two species of these gold-crested warblers 

 being common in North America, in precisely the same 

 latitudes, yet trtally distinct from those of Europe.'' It 

 is by such questions, of which every class of animals 

 will furnish innumerable examples, that closet theories 

 must be tried : at the same time, they will at once point 

 out the very distinct nature of local dispersion from that 

 of geographic distribution, properly so called. 



(10.) Another theory supposes that the same spe- 

 cies of animal or plant has been originally placed in 

 many different regions : in other words, to have been 

 at the period of their first existence locally diffused in 

 countries widely distant. Hence it is, that nearly every 

 country in the old world has a particular breed or race 

 of the horse, ox, sheep, and dog ; all of which, in com- 

 mon language, are terrr> ^d the original breed of the par- 

 ticular countries wherein they are found. Little need 



