‖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.