CHANGES IN THE EGG. 289 



At the expiration of the full period of incubation 

 the white has entirely disappeared, leaving, as the 

 only trace, a few dry flakes of membrane, and an 

 earthy residuum. The yolk also disappears, being 

 taken into the body of the chick. It might ap- 

 pear to the unthinking person, that the conversion 

 of the fluid matters forming the egg, in its fresh 

 state, into the solid and fleshy constituents of the 

 chick, must be attended with increase of weight. 

 It appears a natural supposition, that the egg con- 

 taining a chick should weigh considerably more 

 than it did at first. Such, however, is not the case 

 in reality ; the egg actually weighs less at the ex- 

 piration of the period of incubation than it did at 

 its commencement, having lost about one-sixth 

 part of its entire weight during that time. This 

 loss consists chiefly of the loss of water by evapo- 

 ration from the surface of the egg-shell. 



It may be naturally asked, What has been the 

 exciting cause which has produced the wonderful 

 phenomenon of the development of a living bird 

 from an apparently lifeless spot, floating in the 

 contents of the egg-shell? When we remember, 

 that in artificial incubation, heat is the only agency 

 employed to awaken life in the shell is it to be 

 u 



