Zona pellucida. [NL.](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[NL.](Biol.), a radiately striated membrane situated next the yolk of an ovum, or separated from it by a very delicate membrane only.