CHAP. IV. 



STKUCTUKE OF HEN'S EGG. 



617 



CHAPTER IV. 



HATCHING AND BREEDING. 



TWO conditions are absolutely necessary in the hatching of a fowl's 

 egg, namely, heat and moisture. Without heat the germ of life con- 

 tained within the shell, its envelope, would never develop, but would 

 die from inanition. Without moisture the absorption by the outer air 

 of the moisture within the shell, would be so great that the chicken, if it 

 remained alive until the time of hatching, would find itself surrounded 

 by a tough shell and a tougher membrane, through which it would be 

 utterly unable to penetrate. Whether the chick ever reaches this stage 

 or not depends upon the dryness of the atmosphere by which it is sur- 

 rounded, for if the absorption be too great, then the embryo will die 

 at an earlier stage. 



It is important to bear in mind that the egg is the method designed 



ABC E M FJ I K G 



Fig. 171. Section of Hen's Egg. 



by nature for the protection of the embryo, which, in the case of birds, 

 passes through the stages of development outside the body of the 

 mother. In the case of nearly all birds the final stage, after the laying 

 of the egg, is due to the attention and care of the parents, who 

 incubate by heat from their own bodies. A hen's egg has been very 

 expressively described by Mr. Matthieu Williams as " a sermon and a 

 miracle, for though scientists can tell us the component parts of our 

 morning egg, they have never been able to say why from one comes a 

 ' little rid hin,' and from another a bantam." It is formed of several 

 parts, which may (fig. 171) be briefly described as follows : 



A, the shell composed of carbonate of lime, phosphate of lime, 

 and animal glutin ; 



B, the outer membrane, adhering to the shell ; 



