During the breeding season, hormonal changes cause the internal testes of males to swell to more than 1000 times their normal size, and the ovaries and oviduct of females to increase in size in preparation for egg fertilization and egg development. During copulation, the male’s cloaca contacts and ejects sperm into the cloaca of the female. This is sometimes referred to as the "cloacal kiss." The sperm travel to the oviduct where they can be stored for long periods in sperm storage tubules. If all goes well, the sperm penetrate through the wall of the ovum (egg) and fertilization takes place. During the first stage of embryonic development, known as the blastocyst stage, the egg shell develops. Ovulation and laying take about 24 hours, so females produce at most a single egg per day.