ZONA

‖Zo″na (?), n.; pl. Zonæ (#). [[L., a girdle. See Zone.]] A zone or band; a layer. Zona pellucida. [] (Biol.) (a) The outer transparent layer, or envelope, of the ovum. It is a more or less elastic membrane with radiating striæ, and corresponds to the cell wall of an ordinary cell. See Ovum, and Illust. of Microscope. (b) The zona radiata. — Zona radiata [] (Biol.), a radiately striated membrane situated next the yolk of an ovum, or separated from it by a very delicate membrane only.