xviii INTRODUCTION. 



serene sky and a bright sun, while the terrestrial animals re- 

 main involved in darkness and exposed to all the fury of the 

 tempest. In twenty-four hours it can change its climate, and 

 sailing over different countries, it will form a picture exceeding 

 the powers of the pencil or the imagination. The quadruped 

 knows only the spot where it feeds, — its valley, mountain, or 

 plain ; it has no conception of the expanse of surface or of 

 remote distances, and generally no desire to push forward its 

 excursions beyond the bounds of its immediate wants. Hence 

 remote journeys and extensive migrations are as rare among 

 quadrupeds as they are frequent among birds. It is this 

 desire, founded on their acquaintance with foreign countries, 

 on the consciousness of their expeditious course, and on their 

 foresight of the changes that will happen in the atmosphere, 

 and the revolutions of seasons, that prompts them to retire 

 together at the powerful suggestions of an unerring instinct. 

 When their food begins to fail, or the cold and heat to incom- 

 mode them, their innate feelings and latent powers urge them 

 to seek the necessary remedy for the evils that threaten their 

 being. The inquietude of the old is communicated to the 

 young ; and collecting in troops by common consent, influ- 

 enced by the same general wants, impressed with the approach- 

 ing changes in the circumstances of their existence, they give 

 way to the strong reveries of instinct, and wing their way over 

 land and sea to some distant and better country. 



Comparing animals with each other, we soon perceive that 

 smell, in general, is much more acute among the quadrupeds 

 than the birds. Even the pretended scent of the Vulture is 

 imaginary, as he does not perceive the tainted carrion, on 

 which he feeds, through a wicker basket, though its odor is as 

 potent as in the open air. This choice also of decaying flesh 

 is probably regulated by his necessities and the deficiency of 

 his muscular powers to attack a living, or even tear in pieces a 

 recent, prey. The structure of the olfactory organ in birds is 

 obviously inferior to that of quadrupeds ; the external nostrils 

 are wanting, and those odors which might excite sensation 

 have access only to the duct leading from the palate ; and even 



