102 GEOGRAPHICAL DISTRIBUTION. 



probably be caused by the heat ; and Buffon says 

 that instead of warmer, they seek colder climates. 

 The house-swallow, 1 which remains with us till 

 October, is stated to winter in Africa, so that its 

 object is evidently a warmer climate. It is re- 

 markable that the birds of this tribe, when they 

 visit us in the spring, return to their old haunts. 

 Dr. Jenner ascertained this by cutting off two 

 claws from the foot of a certain number, several 

 of which were found in the following year, and 

 one was met with after the expiration of seven. 

 The instinct that directs these little beings so 

 unerringly across continents and oceans, and 

 leads them to their native clime is wonderful, 

 and inexplicable under any other principle than 

 that of Divine superintendence. But upon this 

 I shall have occasion to enlarge hereafter. 



From what is here stated, it seems most pro- 

 bable, that it is not only the increasing heat of 

 the southern regions which induces the swallow 

 to seek a less ardent clime to transact her loves 

 and rear her young ; but also a stimulus, caused 

 by the heat, acting upon her organization, which 

 aids to accomplish that important purpose, and 

 is the leading star by which her Creator impels 

 her to the land of her own nativity, and which 

 is destined to be that of her offspring. Only 

 the swift leaves a colder climate for one more 

 genial and better suited to the same purpose, 



1 Hirundo rustica. 



