298 THE REASON WHY : 



*' The ynlke of the egge cannot be without the whyte, nor the 

 whyte -without the yolke ; no more rnaye the clergy and the 

 lordes be one without another." FROISSAKT'S CHROMICLKS. 



the most wonderful operations of instinct. The instrument which 

 it employs is a small protuberance on its upper mandible, called 

 the bill-scale, which has no other use, and accordingly drops off 

 soon after the bird is hatched. 



957. This bill-scale is provided with a sharp cutting edge, the use of which is to 

 cut through the membrane which lines the shell. Were it not for this, the shell 



would break, while the membrane would stretch, and the chicken would still 

 remain a prisoner. 



The egg-shell is formed by a solidified deposit from the blood-vessels of the 

 egg-duct of the parent bird ; but it is permeable to air, which is necessary to the 

 life of the embryo. The shell is lined by two membranes : the one external and 

 rough, so that it adheres to the shell ; the other exceedingly smooth, so that it 

 allows of the rotation of the contained parts. And, at one extremity of the egg, 

 there is a little sack hlled with air containing an unusual proportion of oxygen, 

 which is employed in giving vitality to the awakening germ. 



958. Wliy can a recently hatched bird exist for many hours 

 without food ? 



Because a portion of the yolk of the egg yet remains in its 

 body, and by that it continues to be nourished. 



959. The wisdom of this provision is obvious : had the first-born bird needed 

 immediate food, it must either have been starved, or the mother, whilst providing 

 for it, must have deserted her other e.gys, and thus destroyed the rest of her family : 

 but, under this arrangement, the mother may, without injury to her first-born. 

 continue to sit on her nest till all her little ones are hatched, which somet.jaes 

 takes more than a day. 



