372 CLASS XVI. 



especially remarkable in some species, in tlie imitation of sounds 

 and of songs they have heard. Admirable also is their instinct, 

 which, as in the insect at the last period of its life, has special 

 regard to the preservation of the species and the care of the young. 

 The artistic manner in which some build their nest, the solicitude 

 with which they tend it, Avith which they conceal it from the eye 

 of their enemies, the skill with which they contrive to divert the 

 persecutions of other animals, and of man, from the place where 

 their nest is, all tliis reminds us of similar exhibitions in the insect 

 tribes. 



The ordinary abode of birds is in connexion with the disposi- 

 tion of their moving power; the swimming membrane of the feet, 

 for example, in the ducks, &c. at once indicates their resort to 

 water. Some are almost entirely restricted to abide in water, as the 

 Aptenodytes, which only comes to land for the brooding of her eggs. 

 The waders live in morasses and on the shores of rivers; whilst 

 some are able, if they have long wings, to make their nest in trees, as 

 the herons. The gallinaceous birds live principally on the ground; 

 climbing birds, like the monkeys and squirrels amongst mammals, 

 in the woods. Amongst the songsters and the birds of prey are 

 some which fly to a great height, and live partly on the ground, 

 partly in trees. Some birds live only on mountains. Between the 

 covering also of the body, the peculiar arrangement of the feathers, 

 and the usual abode of birds, a striking correspondence prevails. 

 Tlie thick, smooth and often shining feathers of the water-birds 

 may afford us an example of this. 



The geographic distribution of birds deserves, in fine, some 

 notice. Towards the poles the number diminishes both of genera 

 and species ; it increases in the temperate zones, and in the torrid 

 zone of our earth there are found, just as in the other classes of the 

 animal kingdom and the natural families of the vegetable kingdom, 

 the greatest richness and the most abundant variety of forms. The 

 genera of birds, of which Em-ope possesses species, do not form one 

 half of the whole number that is received for the species of birds 

 discovered on our earth. The swimming-birds are especially nu- 

 merous near the poles, and, whilst the number of their species forms 

 scarcely tt of that of the entire class, in Sweden it amounts to 

 more than |, in Greenland to more than h of the whole number of 

 species of birds occurring in those countries. The genera Aha, 



