296 



THE REASON WHY : 



" Meanwhile the tepid caves, and pens, r.i.i sLoarcs, 

 Their brood as numerous hatch, for the e</g that soon 

 Bursting with kindly rupture forth disclos'd 

 Their callow young." MILTON. 



952. Why have some sp&ei&s of birds extremely soft bilh f 



Because the class of birds thus famished hare to stize their 

 prey quickly, as they often catch it while it is on the wing ; though 

 they do not fly after it, rapidity of motion both in darting at the 

 food, and in opening and shutting both with firmness and sharpness 

 at the tip, are the requirements of snch a bill ; and lightness in its 

 general structure is essential to quick motion. These bills are, 

 in very many species, so thin and weak that they are not able 

 to break the coat of a vegetable seed. 



953. Why do birds lay egg* ? 



Because, to bear their yonng 

 in any other manner, would 

 eneumber ike body, and mate- 

 rially interfere with the active 

 movements that are charac- 

 teristic of the feathered tribes. 

 As soon as an egg becomes 

 large and heavy enough to 

 be cumbersome to the bird, 

 it is removed from the body, 

 and deposited in a nest, which, 

 in some respects, may be re- 



t?arded as em artificial womb. 



A shell impervious to air protects the germ of life within, until 

 from two to twenty eggs have accumulated, and then, although 

 laid at different intervals, the incubation commences, and the 

 young birds are hatched at the same time. 



954. Why do the eggs of birds contain two distinct substances, 

 the white and the yolk ? 



The white, or albumen, of the egg, supplies nourishment to the 



