Archegonium, the feminine sex organ in ferns and mosses. An archegonium also occurs in some gymnosperms, e.g., cycads and conifers. A flask-shaped structure, it consists of a neck, with one or more layers of cells, and a swollen base—the venter—which contains the egg. Neck-canal cells, located above the egg, disappear because the archegonium matures, thus producing a passage for entry of the sperm. The sperm are produced within the corresponding male sex organ, the antheridium.

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