THE EGG 23 



nature of the shell, as there is not room for two eggs side by side 

 in the lower part of the body-cavity. 



The ovary lies at the anterior end of the kidney attached 

 by a fold of the peritoneum (mesovarium) to the dorsal wall of 

 the body-cavity. In a laying hen ova of all sizes are found from 

 microscopic up to the fully formed ovum ready to escape from 

 the follicle. Such an ovary is shown in Figure 4; the gradation 

 in size of the ova will be noticed up to the one fully formed and 

 ready to burst from its capsule. At 5 in this figure is shown a 

 ruptured follicle, and the ovum w^hich has escaped from this 

 follicle is shown in the oviduct at 8. It will be seen that the part 

 of the definitive hen's egg produced in the ovary is the so-called 

 yolk. The blood-supply of the very vascular ovary is derived 

 from the dorsal aorta, and the veins open into the vena cava 

 inferior. 



The oviduct is a large coiled tube (Fig. 4) which begins in a 

 wide mouth with fringed borders, the ostium tubce abdominale 

 (funnel or infundibulum) opening into the body-cavity near the 

 ovary. It is attached by a special mesentery to the dorsal wall 

 of the body-cavity, and opens into the cloaca. The following 

 divisions are usually distinguished: (1) the funnel or infun- 

 dibulum, (2) the albumen secreting portion, (3) the isthmus, 

 (4) the uterus or shell-gland, (5) the vagina (Fig. 4). The albu- 

 men secreting portion includes all of the coiled tube; the isthmus 

 is a short section next to the dilated uterus, and the vagina is 

 the short terminal portion opening into the cloaca (Figs. 4 and 5). 



The formation of an egg takes place as follows: the yolk, or 

 ovum proper, escapes by rupture of the follicle along a preformed 

 band, the stigma (Fig. 4-4), into the infundibulum, which swallows 

 it, so to speak, and it is passed down by peristaltic contractions 



ova are shown in the oviduct at different levels; normally but one ovum 



is found in the oviduct at a time. 



1, Ovary, region of young follicles. 2 and 3, Successively larger follicles. 

 4, Stigmata, or non-vascular areas, along which the rupture of the follicle 

 takes place. 5, Empty follicle. 6, Cephahc lip of ostium. 7, Funnel of 

 oviduct (ostium tubae abdominale). 8, Ovum in the upper part of the ovi- 

 duct. 9, Region of the oviduct in which the albumen is secreted. 10, Albu- 

 men surrounding an ovum. 11, Ovum. 12, Germinal disc. 13, Lower seg- 

 ment of albumen-secreting portion. 14, Lower part of the oviduct ("uterus," 

 shell-gland). 15, Rectum. 16, Reflected wall of the abdomen. 17, Anus, or 

 external opening of cloaca. 



