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.
The oviduct of Lumbricus) are parts of the coelomic wall itself, which have grown out to the exterior.
We have here clearly a case of a true coelomoduct performing the function of an oviduct in both leeches and Eudrilidae.
In the former, the duct, leading from the ovarian sac, and swelling along its course into the spherical sac, the "spermatheca," is highly suggestive of the oviduct and receptaculum of the Eudrilidae.
In some forms this receptacle acquires a separate external opening remaining connected with the oviduct internally.
M The "bell" swallows the matured embryos and passes them on into the uterus, and thus out of the body via the oviduct, which opens at one end into the uterus and at the other on to the exterior at the posterior end of o.-- the body.
(The ovary (a) leads into (bb) the oviduct, which is joined at (g) by the duct of the yolk-glands (h, h, Y).
A, a segment of Bothriocephalus latus, showing the generative organs from the ventral surface; ex., excretory vessels; c., cirrus; c.p., cirrus pouch; v.d., vas deferens; v.o., vaginal opening; v., vagina; sh.g., shell-gland; od., oviduct; ov., ovary; y.g., yolk-gland; y.d., its duct; ut., uterus; u.o., uterine opening; the testes are not visible from this side; X 23 (from Sommer and Landois).
B, anterior portion more highly magnified (from Marshall and Hurst, after Sommer); cs, cirrus sac; d, ductus ejaculatorius; f, female aperture; o, ovary; od, oviduct; p, penis; s, shell-gland; t, anterior testis; u, uterus; va, vp, vasa deferentia; us, vesicula seminalis; y, yolk-gland; yd, its duct.
The ovary (a) leads into (bb) the oviduct, which is joined at (g) by the duct of the yolk-glands (h).
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.
A canal (Laurer's canal) leads from the oviduct or yolk-duct to the dorsal surface.
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.
Germary and ovary paired; oviduct absent; young viviparous.
True viviparity, that is the development of the ova within the oviduct, is very rare, occurring only in one case among the Amphineura and in some aquatic and pulmonate Gastropoda.
The yolk prepared by the latter is conducted by one or more specialized ducts to the oviduct and the point of union is distinguished by the opening of a " shell-gland " which secretes a membrane around the conjoined mass of ovum and yolk.
From this junction there proceeds an oviduct or " uterus " (paired or single) which before opening to the exterior expands to form a muscular protrusible pouch - the bursa copulatrix.
Stevens the socalled oviduct acts only as a "sperm-duct" or receptaculum seminis.
B, buccal mass; m, retractor muscles of the buccal mass; ov, ovary; od, oviduct; i, coils of intestines; ao, aorta; c', left auricle; c, ventricle.