From the left ovary (the right one is wasted) the egg yolk is dropped (oocytes). These, while they pass through the oviduct, acquire the egg white or albumen and lastly the eggshell. Therefore, the egg formation occurs throughout the oviduct and lasts, in the hen, 24 hours.

The fecundation is always undertaken in the upper part of the oviduct where the union of the rooster's sperm and the hen's egg takes place. When this occurs, the egg becomes fertile producing the germ disc will be observed in a reduced time. Otherwise, it will not develop any new being.