440 



EMBRYOLOGY OF THE CHICK 



particles of carbonates and phosphates of calcium and magnesium. The 

 inner surface of the shell is composed of a thin but dense layer of in- 

 organic salts. After the shell has dried, it is quite porous, thus making 

 the passing of gases and water-vapor quite easy. 



There is a tough shell membrane lining the inner portion of the 

 shell. It is composed of a double sheet of fibrous connective tissue which 

 separates at the blunt end of the egg into an air space, becoming larger 

 as time goes by, 



THE REPRODUCTIVE 



One obtains a more thorough 

 the egg in the ovary if a review of 



el 



Fig. 262. 



The reproductive system of the fowl. The 

 figure shows two eggs in the oviduct, whereas 

 normally only one egg is in the oviduct at a 

 time. 6, Blastoderm ; c, cicatrix ; cl, cloaca ; 

 da, dense layer of albumen ; /, empty egg 

 follicle from which the ovum has escaped; a, 

 glandular portion of oviduct ; i, isthmus ; m, 

 mesovarium ; o 1 -o 4 , ovarian ova in various 

 stages of growth ; O 1 , ovum in upper end of 

 oviduct ; O a , ovum in middle portion of ovi- 

 duct (the oviduct has been cut open to show 

 the structure of this ovum) ;os, ostium or in- 

 fundibulum ; ov, ovary containing ova in 

 various stages of growth ; r, rectum ; u. 

 uterus ; v, vitellus ; w, ventral body wall, 

 opened and reflected. (From Duval. ) 



ORGANS OF THE FOWL 



understanding of the development of 

 the entire reproductive organs is un- 

 dertaken. The reproductive organs 

 of the fowl do not develop equally 

 on each side, though they begin de- 

 veloping symmetrically. The right 

 ovary ultimately degenerates, and as 

 far as we know does not function. 

 The left ovary (Fig. 252) and ovi- 

 duct alone carry on the work of the 

 organs. The left organs therefore 

 become quite large. 



A microscopical section of the 

 ovary shows this organ to be com- 

 posed of a great quantity of ova, 

 each ovum being contained in a 

 Graafian follicle (Fig. 253). The 

 ovary itself is suspended from the 

 dorsal abdominal wall by a double 

 fold of the peritoneum called a 

 mesovarium. 



In the hen, the ova vary in size 

 from a very small cell up to the full 

 sized yolk. The oviduct is large, 

 thick-walled and muscular, being 

 convoluted, and having a different 

 structural form in the different 

 parts. As the oviduct is to carry 

 eggs from the ovary to the uterus, 

 there are two openings, one the ab- 

 dominal, which is rather wide and 

 flaring and funnel-shaped, coming 

 in close contact with the ovary. 

 This opening is called the ostium or 

 infundibulum, or the fimbriated 

 opening. This last name is due to 



