18 



THE DEVELOPMENT OF THE CHICK 



The shell-membrane consists of two layers, a thick outer 

 layer next to the shell and a thinner one next the albumen. Both 

 are composed of matted organic fibers (more delicate in the inner 

 than in the outer layer), crossing one another in all directions. 

 At the blunt end of the egg the two layers are separated and 

 form a chamber containing air that enters after the egg is laid 



(Fig. 2). 



The physical characteristics of the albumen are too well 

 known to require description. A dense layer inmiediately next 



BJ 



ML. 



A12,. 



VM. 



YK 



Fig. 2. — Diap;rain of the hen's egg; in section to show relations of the parts. 



A. C, Air chamber. Alb., Albumen. Bl., Blastoderm. Chal., Chalaza. 

 I. S. M., Inner layer of the shell membrane. L., Latebra. N. L., Neck of 

 Latebra. N. P., Nucleus of Pander. O. S. M., Outer shell membrane, p'v. s., 

 Perivitelline space. 8., Shell. V. M., Vitelline membrane. W. Y., White 

 yolk. Y. Y., Yellow yolk. 



to the vitelline membrane is prolonged in the form of two spirally 

 coiled opalescent cords towards the blunt and narrow ends of 

 the egg respectively; these are the chalazae, so called from a 

 fanciful resemblance to hail stones. The two chalazse are twisted 

 in opposite directions. In a hard-boiled e^g it is possible to strip 

 off the albmuen in concentric s])iral layers from left to right from 

 the broad to the small end of the egg. 



