Image from John Anderson, Dept. of Animal Sciences, The Ohio State University. Used with permission.
Looking at the photo, we begin
at the ovary. The ovary is a cluster of various sizes of developing
follicles. The follicle is a sack that contains the developing yolk.
It takes about 10 days for a yolk to grow from a very small size to the
normal size found in eggs. The oviduct is a long tube containing
many blood vessels and glands. The function of the oviduct is to produce
the albumen, shell membranes and the shell around
the yolk to complete the egg. Normally, a yolk is released when the follicle
ruptures (breaks). Then the yolk enters a thin-walled infundibulum,
the first part of the reproductive tract (oviduct). It is in the infundibulum
where the egg can become fertilized if sperm are present. The egg then
passes to the magnum where albumen (egg white) is placed around
the yolk. The egg then passes to the isthmus where the shell membranes
are placed around the egg. The egg then moves to the shell gland
(uterus) where a hard calcified shell is placed around the
developing egg. The egg passes quickly through the vagina just
before it is laid.