zona

Zo"na, n.; pl. Zonæ. Etym: [L., a girdle. See Zone.] Defn: A zone or band; a layer. Zona pellucida. Etym: [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 Etym: [NL.] (Biol.), a radiately striated membrane situated next the yolk of an ovum, or separated from it by a very delicate membrane only.

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