88 
INTRODUCTION. 
also have a much wider range assigned to theitl 
than others; and a very fetv, inhabiting different 
continents, are restricted only by temperature. Thus, 
between the magpie of England, North America, 
and China, specimens of which are now laying be- 
fore us of each locality, not the slightest difference 
can be detected ; and yet these birds are never found, 
in either of these continents, beyond the limits of 
wintery cold. Birds, of all other animals, might 
be thought at first to be exempt from this law of 
nature, seeing that they are such volatile beings, 
and capable of traversing immense distances in sur- 
prisingly short periods. But this opinion is not 
borne out by facts. The common house-swallow of 
Europe might reach America with as much ease as 
the coasts of Africa, and there enjoy the same warm 
temperature, and find as great an abundance of 
insect food. But its course has been ordained 
otherwise. Its Almighty Creator has implanted in 
it the destined route it is to pursue, and from that 
route it never deviates, whether on the right hand 
or on the left. To speculate upon the causes of 
such things would be idle ; we can only wonder at 
the fact and be silent. Sea birds have a much 
wider range than those inhabiting the land ; probably 
because their supplies of food, drawn from the ever- 
waving sea, and the ever-changing depositions of its 
tides, are much more precarious. And yet, even 
among these tribes, great regularity may be observed 
in general within geographic range, although these 
ranges in themselves are much more extensive than 
