906 



CARE AND NOURISHMENT OF THE DEVELOPING YOUNG 



the anterior part (i.e., the ovarian end) of the albumen-secreting portion of 

 the oviduct (figs. 157; 369A). Some of the watery material is added in the 

 isthmus and in the uterus (Romanoff and Romanoff, '49, p. 220). 



e) Formation of the Egg Membranes and Egg Shell. As the egg 

 reaches the isthmus, the shell membranes are formed around the albuminous 

 material. In the upper part of the isthmus, the thin inner membrane is formed, 

 while the thick, coarse, outer membrane is deposited in the posterior parts 

 of the isthmus. These two membranes of the egg expand considerably coin- 

 cident with the passage of a watery albuminous material through their mesh- 

 work into the outer, liquid, albuminous layer while the egg passes through 

 the lower part of the isthmus, and also during the first part of the egg's occu- 

 pancy of the uterus. As a result, the volume of the albumen is increased 

 rapidly and considerably in this general area. 



During the latter part of the period of the egg's residence within the uterus, 

 calcareous concretions or mammillae are deposited upon the external face 

 of the coarse, outer, egg membrane (fig. 369B). Each conical concretion or 

 mammilla is embedded in the outer egg membrane. The broader distal end 

 of the mammila faces outward while the pointed proximal end is attached 

 to the egg membrane (fig. 369B). Small pores appear between the various 

 mammillae. External to the mammillary layer, a spongy layer of collagenous 

 fibers is formed. This spongy layer gradually becomes impregnated with cal- 

 cium salts which lie within the spaces between the spongy fibers and between 

 the mammillary and spongy layers. The calcified spongy layer and associated 

 mammillary concretions form the egg shell. The calcium probably is secreted 

 in the form of bicarbonate which later changes to calcium carbonate. Some 

 calcium chloride and phosphate, together with a calcium-protein substance 

 also are formed. The colored pigments of the egg shell in colored eggs are 



OF ALBUMEN : 

 OUTER LIQUID 



LIGAMENTUM 

 ALBUM 



HALAZA 



SPONGY LAYER ■ 

 GG MEMBRANE 

 AIR CELL 



»«« 





-■i^:«ij-S 



M 



AMMILLARY iffmmi^-^i^^ii^-'^''"^ 

 LAYER ^■ 



SHELL MEMBRANE 



EGGSHELL 



Fig. 369. Structure of the hen's egg. (A and B redrawn from Romanoff and Romanoff, 

 1949. Wiley & Sons, Inc., N. Y. ) (A) General structure of newly laid hen's egg (after 

 Romanoff). (B) Detailed structure of egg shell (after von Nathusius). 



