MIGRATION. 



No act of nature affords so wide a field for speculation 

 as that of the migration of animals. The causes that 

 influence their movements, the power that directs them, 

 the object and importance of the natural laws that govern 

 and impel them to depart from a particular spot and to 

 return to it, at some future time, by the most miraculous 

 and unerring certainty, probably after the lapse of a year 

 or more, are mysteries that require profound consideration 

 before we can attempt to describe, or even to suggest, by 

 what impulse they are guided. 



The inclination to travel from place to place is strongly 

 implanted in by far the largest portion of the animal 

 creation, and it may be fairly considered that the migra- 

 tory far outnumber the non-migratory species. There are 

 two Orders among vertebrate animals the power of loco- 

 motion of which best adapts them for migration — viz. the 

 Orders Aves and Pisces ; and in those Orders we find many 

 species that annually migrate, some that occasionally, some 

 that rarely, and others that never do so. The desire to 

 migrate has been attributed by some to an actual neces- 

 sity, such as scarcity of food ; but that does not fairly 

 account for it, as many of our summer birds leave this 

 country at the time that food is most abundant. We 

 might, with equal right, argue that the animals that 

 hibernate do so on account of the supply of food failing ; 

 but we have already shown, in a previous paper, that such 



228 



