24 



THE DEVELOPMENT OF THE CHICK 



of the oviduct. The escape of the ovum from the follicle is known 

 as the process of ovulation. During its passage down the ovi- 

 duct it becomes surrounded by layers of albumen secreted by 



the oviducal glands. The shell- 

 membrane is secreted in the 

 isthmus and the shell in the 

 uterus (Fig. 5). The ovum is 

 fertilized in the uppermost part 

 of the oviduct and the cleavage 

 and early stages of formation of 

 the germ-layers take place be- 

 fore the egg is laid. The time 

 occupied by the ovum in tra- 

 versing the various sections of 

 the oviduct is estimated by 

 Kolliker as follows: Upper two 

 thirds of the oviduct about 

 three hours (formation of al- 

 bumen), isthmus about three 

 hours (secretion of shell-mem- 

 brane) , uterus twelve to twenty- 

 four hours (formation of shell 

 and laying). These figures 

 are only approximate and it is 

 obvious that they are likely to 

 vary considerably in different 

 breeds of hens. 



Some of the details of these 



Fig. 5. — Uterus (shell-gland) of the 

 hen cut open to show the fully 

 formed egg. (After Duval.) 



1, Cut surface of oviduct, region of remarkable processes deserve 



isthmus. 2 Reflected flap of uterus, attention: the observations of 



3, Egg ready to be laid. 4, Lower 



extremity, or vaginal portion, of the several naturalists demonstrate 



thf o;^ucti,ft:1rclorca''''7':o1,en! that the ripe follicle i. em- 

 ing of the rectum into the cloaca. 8, braced by the funnel of the ovi- 

 ^^^^^^- duct before its rupture so that 



the ovum does not escape into the body-cavity, but into the 

 oviduct itself. Coste describes the process in the following 

 way: "In hens killed seventeen to twenty hours after laying I 

 have observed all the stages of this remarkable process. In 

 some the follicle, still intact and enclosing its egg, had already 

 been swallowed, and the mouth of the oviduct, contracted 



