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 j)ower 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 
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