In some families, as many freshwater snakes, the sea snakes, Viperinae and Crotalinae, the eggs are retained in the oviduct until the embryo is fully developed.
In some forms this receptacle acquires a separate external opening remaining connected with the oviduct internally.
From each ovary an oviduct (fig.
From the oviduct a long duct full of yolk passes backwards almost to the hinder end of the body and ends blindly in a globular dilatation just below the skin.
In these forms the pregnant female, instead of laying eggs, as Diptera usually do, or even producing a number of minute living larvae, gives birth at one time but to a single larva, which is retained within the oviduct of the mother until adult, and assumes the pupal state immediately on extrusion.
Portion of which the ova or spermatozoa are developed, the lower portion serving as an oviduct or vas deferens; the female generative organs open at the middle of the body, the male close to the posterior extremity into the terminal portion of the alimentary canal; from this cloaca a diverticulum is given off in which are developed one to three chitinous spicules that subserve the function of copulation.
We have here clearly a case of a true coelomoduct performing the function of an oviduct in both leeches and Eudrilidae.
In all the species except the African species there is a globular receptaculum seminis opening by two short ducts close together into the oviduct, and in the neotropical species there is in addition a small receptaculum ovorum, with extremely thin walls, opening into the oviduct by a short duct just in front of the receptaculum seminis.
The oviduct of Lumbricus) are parts of the coelomic wall itself, which have grown out to the exterior.