The females of most animals have two functional ovaries, but the hen has only one. The right ovary stops developing when the female chick is hatched, but the left one continues to develop. Th eleft ovary will contain up to about 4,000 tiny ova from which the full-sized yolks will develop when the hen matures. Each yolk or ovum is contained in a thin membranous follicle. Blood vessels in the follicle carry nutrients to the developing yolks. When a yolk matures, the follicle ruptures along a line relatively free from blood vessels known as stigma, and the yolk is released. The yolk is kept intact by the vitelline membrance surrounding it.

Upon release from the follicle, the yolk drops into the body cavity. The the infundibulum, or funnel, engulfs the yolk and starts on its way down the oviduct. The oviduct is more than two feet long and is lined with glands which secrete the materials for the albumen, shell membranes, and shell. Twenty-four hourse or more are required from the time the yolk is released until the completed egg is laid.

The germinal disc from which new life forms is attached to the yolk of the egg. Surrounding and protecting the germ cell and yolk is the white or albumen consisting of several layers.

The albumen is somewhat elastic, and it is a shock-absorbing, semi-solid material with a high water content. The albumen and the yolk of the egg serve as food for the growing embryo during the incubation period. On opposite sides of teh yolk are two twisted, whitish cord-like objects know as chalazae. They anchor the yolk and keep it from rising and touching the shell. Nature provided them also to serve as a rotating axis to keep the germ cell on the top side of the yolk and, therefore, next to the heat of te hen's body. So, the yolk and albumen work together to protect and sustain the life of the growing embryo.

Around the albumen and yolkk are two shell membranes and the shell itself. These give protection to both the yolk and albumen, and the shell provides for an exchange of gases and serves as a method of conserving the food and water supply incased within the shell for the benefit of the devloping embryo.

Shortly after the ovum has been released from the hen's ovary, it is picked up by the funnel or infundibulum. Sperm from the male are found in the folds of the infundibulum. Soon after the ovum is picked up by the infundibulum, many sperm contact the germinal disc, but only one unites with the germ. Thus fertilization occurs about 24 hours before the egg is laid.

Since the fertilized germinal disc, or blastoderm, spends about 24 hours in the warmth of the hen's body (about 107 degrees F.) while the egg i sbeing completed, certain stages of embryonic development occur during that time. About 3 hours after fertilization the newly formed single cell divides and makes two cells. Then there are 4, 8, 16, and so on. Cell division continues until there are many cells grouped in a small, whitish spot visible on the upper surfavce of the egg yolk.