72 THE STRUCTURE OF THE FOWL 



calcareous material with small air - spaces 

 between them. The outermost layer or shell 

 cuticle is thin, delicate, and structureless, 

 but porous ; while the middle layer is spongy 

 and formed of a meshwork of fibres. Within 

 the shell is the shell-membrane, consisting of 



a-c 



Fig. 42. — Diagram of the Parts of a fully formed Egg. 



bl., blastoderm; yk.i, white yolk: yk.2, yellow yolk; ch.al., chalaziferous layer 

 of albumen; al.i, dense albumen; al.2, fluid albumen; ch., chalaza; s.m., shell- 

 membrane; sh., shell; a-c, air-chamber. 



an outer thick and an inner thin layer. At 

 the broader end of the egg the two layers of 

 the shell-membrane are separated from each 

 other to form the air-chamber — a space of 

 considerable importance in relation to the 

 respiration of the unhatched chick. Within 

 the shell-membrane is the albumen, or " white 



