i8o 



ANATOMY or THE DOMESTIC FOWL 



2). . The yolk is surrounded by a very delicate membrane called the 

 vitelline membrane. The empty sac now shrinks and finally 

 disappears. 



The Egg. — ^The principal divisions of the egg are the yolk, the 

 albumin outside of the yolk content, the shell membranes and the 

 shell (Fig. 58). As stated, the yolk is formed in the ovary, leaving 

 the other three portions to be formed in the oviduct. 



• Fig. 57. — Section through the ovary, of the hen. u, The ova. d. An ovum 

 beginning to receive deposits of yolk material, c. Ova farther advanced in yolk 

 formation. 



The albumin may be subdivided into, first, a thin layer of albumin 

 lying close aroimd the yolk; second, a thick layer of albumin lying, 

 at the outer periphery; and third, a modification of the albumin 

 called the chalazae. The chalazse are twisted, dense cord-like 

 structures at either pole of the yolk, one end of which is adherent 

 to the vitelline membrane and the other to the inner membrane 

 surrounding the albumin. The chalazae thus act as stays to this 

 structure, which is carrying a delicate burden, the blastoderm. 



