Pronunciation: (kôr'ē-on", kōr'-), [key]
1. Embryol.the outermost of the extraembryonic membranes of land vertebrates, contributing to the formation of the placenta in the placental mammals.
2. Zool.the membrane around the eggs of certain insects, secreted by cells of the ovary.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.