170 HABITS OF BIRDS. 



lightened. But even boiling water does not render 

 the shell more fragile ; and though the water should 

 soften it, upon drying in the air it would become as 

 hard as at first*." It is well remarked by Mr. 

 Yarrel, that the shell is rendered more brittle by 

 the process of hatching, during which the egg of 

 the common fowl loses on. an average eight grains a 

 day, the moisture being partly evaporated and partly 

 absorbed, and the lining membrane at the same time 

 becoming partially separated f. 



Eggs fractured by the included Chick. 



Though the fracture of the shell usually extends 

 round the whole circumference, yet the chick is 

 sometimes contented with performing only about 

 three-fourths of the task. When this has been done, 

 the bill is not required to complete the separation, 

 which is effected more easily and speedily by push- 

 ing with the whole mass of its body, using the feet 

 as a lever. By thus continuing to push the body 

 forwards, a movement which is frequently repeated, 

 the chick gradually raises the upper portion of the 

 shell, and at length tears all the fastenings; and if 

 any part hold out, that becomes a sort of hinge which 

 permits the lid, as we may call it, to be thrown on one 



. * Reaumur, as before. f Zool. Journ. ii, 436. 



