OF NATURAL HISTORY. 505 



but; when cUfturbed, they migrate to another commodioug 

 place, and erect new habitations. 



From the fa(fts which have been enumeratedj it is appar- 

 ent, that the principle of migration, or ihe defire of chang- 

 ing fituations, is not confined to particular birds, but ex- 

 tends through almofl the whole fyllem of animation. Men, 

 quadrupeds, birds, fiihes, rei)tiles, infedls, all aiford ftril^ing 

 examples of the migrating principle. From the fame fa£ls 

 it is equally apparent, that the general motives for migrating 

 are fimilar in every clafs of animals. Food, multiplication 

 of fpecies, and a comfortable temperature of air, are evident^ 

 ly the chief caufes which induce animals to remove from one 

 place to another, or, what amounts to the fame thing, from 

 one climate to another. Partial emigrations, or emigrations to 

 fmall diftances, are prompted by the fame inftin^tive motives 

 which induce animals of a different ftrudlure to undertake 

 long and fatiguing excurfions. But, previous to aflual mi- 

 gration, what are the peculiar feelings of different animals, 

 and what fhould flimulate them to proceed uniformly in the 

 direction that ultimately leads them to the fituations moft 

 accommodated to their wants and their conftitutions, are 

 myflieries, with regard to which, like every other part of the 

 oeconomy of Nature, it is the duty of philofophers, inftead 

 of attempting to pufh their inquiries beyond the bounds of 

 human ability, to obferve a refpe£lable filence. 



