oviduct(redirected from accessory oviduct)
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a female reproductive duct (usually paired) that serves mainly for the passage of mature eggs, or ova, that have formed in the ovary. The oviduct may be the direct continuation of the ovary (roundworms, arthropods, and echinoderms), or it may be completely isolated from the ovary. In the latter case, the oviduct opens anteriorly into the coelom and posteriorly into the cloaca (most vertebrates) or to the surface (annelid worms and mammals). Sexual funnels of annelid worms serve as the oviducts; most vertebrates have müllerian ducts, which develop from the primary renal duct. The oviducts of sturgeons and Holostei lie next to the ovaries. In most bony fishes the oviducts and ovaries are fused.
The egg is usually propelled through the oviduct by the contraction of the muscular walls or by movement of the cilia of the epithelium lining the cavity of the duct. The oviduct usually has various membranes. Its walls secrete coating substances; sometimes the substances are elaborated only by special regions of the ducts. For example, cephalopod mollusks have a special oviduct gland, and cartilaginous fishes have a shell gland.
The portion of the oviduct in which the eggs or embryos mature is called the uterus. Mammalian eggs are fertilized in the fallopian, or uterine, tubes, which are situated above the uterus. The terminal portion of the oviduct in organisms marked by internal fertilization (with the oviduct opening to the exterior) is called the vagina.