BIRDS. 317 



the removal of putrefying substances, which would soon taint 

 the atmosphere, and spread disease and death around. Many 

 hirds, besides those we have named, share in this labour, con- 

 verting into nourishment that which would otherwise prove 

 baneful. Among the mammiferous animals, we find some 

 that prey upon the helpless and the dead; and thus the carni- 

 vorous tribes, both of birds and quadrupeds, carry into effect 

 the same beneficent provision. But they are not the sole, 

 though they are the most powerful, workers ; there are others, 

 both on land and water, whose diminutive size is more than 

 compensated by their countless numbers. Let us revert to 

 some of the invertebrate animals, whose habits have been 

 briefly noticed, and see how numerous are these labourers, 

 how different their structure, yet how effectually they all work 

 together. Even in the brief space to which we have been 

 restricted, we have enumerated, as devourers of organised 

 matter in a state of decay, Infusoria, Star-fishes, Earth- 

 worms, Crustacea, Insects, Mollusca, Fishes, Crocodiles, and 

 we now add Birds and Mammals. Each individual acts for 

 himself alone; yet all unconsciously co-operate in carrying out 

 one harmonious design. Without the ceaseless efforts of these 

 heterogeneous labourers, the air, the rivers, and the seas 

 would alike become loaded with impurities, and the earth 

 would soon be converted into one great charnel-house. The 

 wisdom by which a comprehensive scheme for preventing this 

 result has been formed, and the providence by which it has 

 been sustained, speak alike of HIM by whom these animated 

 tribes have been called into existence, and have been gifted 

 with their several capacities. 



Migration. At the approach of winter, there are various 

 birds which make their appearance pretty nearly at the same 

 time each year, and leave us early in the spring. They have 

 arrived from regions further north, and have made our islands 

 the southern limit of that periodical change of residence to 

 which we give the term migration. There are others whose 

 appearance in spring we welcome, not only because of the 

 beauty of their flight or their plumage, or the cheerfulness of 

 their notes, but because we know from experience that these 

 feathered visitants are the harbingers of brighter skies and 

 renovated verdure. These lovely heralds of the spring stay 

 with us during the summer, and then wing their way to the 

 south. The British Islands constitute the northern limit of 

 VOL. ii. F 



