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 
Ixolliker 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 
Fig. 5. — Uterus (shell-gland) of the 
hen cut open to show the fully 
formed egg. (After Duval.) Some of the details of these 
1, Cut surface of oviduct, region of remarkable processes deserve 
breeds of hens. 
isthmus. 2, Reflected flap of uterus. 
3, Egg ready to be laid. 4, Lower ; 
extremity, or vaginal portion, of the several naturalists demonstrate 
oviduct. 5, Rectum. 6, Opening of t ee eee BATTS . 
: : - at ; ollicle is - 
the oviduct into the cloaca. 7, Open- that the ripe ; follic le » ee 
ing of the rectum into the cloaca. 8, braced by the funnel of the ovi- 
Cloaca. duct before its rupture so that 
attention: the observations of 
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 
