Fig. 1.

Schematic drawing of an avian oviduct. After ovulation, the oocyte is incorporated into the infundibulum part of the oviduct, and the sperm ascending the oviduct fertilizes the oocyte within 15 min of ovulation. After fertilization, the surface of the zygote is enveloped by several egg envelopes (i.e., albumen, shell membrane, egg shell and cuticle) through the passage of the oviduct, and is oviposited outside of the body. The position of the utero-vaginal junction is indicated by an arrow. The approximate time of zygote residency within each part of the oviduct is also indicated.