00 INTRODUCTION. 



also hare a much wider range assigned to them 

 than others; and a very few, 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 



