CLASS-BOOK OF ZOOLOGY. 65 



SECTION XIII. 



II. ORNITHOLOGY. 



§ 250. Birds are warm-blooded, oviparous animals, pro- 

 vided with two wings and two feet, a horny, toothless 

 bill, and a body covered with feathers. 



§ 251. The flying of birds is facilitated by making them- 

 selves specifically lighter : an effect produced by inflating 

 with air, through the lungs, certain delicate membranous 

 cells, situated under the shoulders and below the hind- 

 part of the body ; as well as by filling with air the hollow 

 bones of the shoulders. 



§ 252. The formation of the bird's embryo in the egg 

 is effected by natural or artificial heat of about 96° Fah- 

 renheit, during a longer or shorter time, either by placing 

 the egg under the parent bird, or by putting it in a breed- 

 ing-machine. 



§ 253. The remarkable metamorphosis of an inanimate 

 egg, as of a hen, for instance, to an animate being, takes 

 place within the space of twenty days. At the end of 

 the second day the first moving of the heart is perceptible, 

 and on the fifth the whole frame of the little creature can 

 be distinctly seen in motion. The feathers make their 

 appearance in a fortnight. At the commencement of the 

 fifteenth day the chicken begins to breath, and on the nine- 

 teenth it is able to peep. 



§ 254. The use of birds to man is very considerable. 

 Birds of prey devour dead carcasses, mice, and rats; 

 Warblers feed on insects, which, from their numbers, 

 would otherwise destroy our fields, gardens, and fruit; 

 the gallinaceous or hen-like birds regale us with their flesh 

 and eggs ; and the water-birds furnish us with eggs, flesh, 

 feathers, and down. 



§ 255. Birds are also, on account of their beautiful 

 plumage, graceful motions, skill, attention, memory, do- 

 cility, and attachment to man, the greatest ornament of 

 the animal kingdom. 



6* 



