On the surface of every egg yolk there can be seen a tiny, whitish spot called the blastodisc. This contains a single female cell. If sperm is present when a yolk enters the infundibulum, a single sperm penetrates the blastodisc, fertilizing it and the blastodisc becomes a blastoderm. Technically, the blastoderm is the true egg. The first stages of embryonic development have begun and continue until the egg is laid.
Development then subsides until the egg is incubated.
After fertilization, the egg can develop and become a chick. Only fertilized eggs grow into chicks. The chicks grow and become adult birds. The oviduct is a tubelike organ lying along the backbone between the ovary and the tail. In a mature hen it is approximately 25 to 27 inches long.