egg

Mature female reproductive cell produced by the ovary, which, after fertilization by a spermatozoon, enables the embryo to develop.

nucleus

Organelle containing a cell’s genes and controlling its activities.

zona pellucida

Fine granular coat composed of mucopolysaccharides covering the egg; it allows a single spermatozoon to penetrate the egg, which then becomes impermeable to others.

cytoplasm

Clear gelatinous substance surrounding the various cellular structures.

nucleolus

Small spherical body located inside the nucleus, within which the ribosomes, or protein-synthesizing structures, are produced.

corona radiata

Collection of granular cells that forms a protective crown around the egg.