In young birds both oviducts are almost equal in size, but the right soon degenerates into an insignificant strand.
Oviducts of Oligochaeta, sperm ducts of Phreoryctes, the coelomoducts occupy, like the nephridia, two segments, the funnel opening into that in front of the segment which carries the external pore.
To this category will belong the oviducts in Teleostean fishes and probably the gonad ducts in several groups of invertebrates.
The oviducts are always short trumpet-shaped tubes and are sometimes reduced (Enchytraeidae) to merely the external orifices.
It is possible, however, that those oviducts belong to a separate morphological category, more comparable to the dorsal pores and to abdominal pores in some fishes.
The sperm ducts are usually longer than the oviducts; but in Limicolae both series of tubes opening by the funnel into one segment and on to the exterior in the following segment.
While the oviducts always open directly on to the exterior, it is the rule for the sperm ducts to open on to the exterior near to or through certain terminal chambers, which have been variously termed atrium and prostate, or spermiducal gland.
13, od) leads, and in some of the more primitive insects (bristle-tails, earwigs, may-flies) the two oviducts open separately direct to the exterior.
- Ovaries of Cockroach, with Oviducts Od and Colleterial Glands CG.
The paired oviducts and vasa deferentia are, as we have seen, mesodermal in origin.
In the female the ovary is a large unpaired organ from the anterior end of which arise two oviducts, and connected with the latter are a pair of large so-called copulatory pouches, which perhaps act as receptacula seminis.
These and the oviducts lie on the anterior half of the body; but the oviducts themselves soon unite to form a single tube of great length, which runs backwards to its posterior extremity, terminating in the genital orifice close to the anus, In the male, on the contrary, this orifice is situated in the anterior half of the body, not far behind the mouth.
The ovary is double, and the oviducts open by a median ventral pore about the middle of the body; in this region there is a second swelling.
E., the connexions of the generative organs, lettering as above: o.d., o.d., oviducts; f., fertilizing canal; X 30.
Many lizards, however, retain the eggs in the oviducts until the embryo is fully developed; these species then bring forth living young and are called ovo-viviparous by purists.
The cloaca is often very large; the nephridia and oviducts may open into it, and the eggs lodge there on their way outwards; they are thrown out, as are the faecal masses, by an eversion of the cloaca.
The ovaries are attached to the side walls of the trunk region; between them and the body wall lie the two oviducts whose inner and anterior end is described as closed, their outer ends opening one on each side of the anus, where the trunk joins the tail.
Temporary oviducts are formed between the "spermduct" and the germinal epithelium at each oviposition.
Thus the condition in the Dermaptera is more primitive than in any other Pterygote order except the Ephemeroptera (Mayflies) which are still more generalized, the primitive mesodermal ducts (oviducts and vasa deferentia) opening by paired apertures as in the Crustacea.
There are two series of ovaries extending through a large part of the body and accompanied by two uteri; the latter open by two oviducts which debouch into an atrium which also receives the intestine and a single receptaculum seminis, and is continued backward as the cloaca; this opens posteriorly.
The ducts are present only as a single pair, except in one genus of parasitic Isopoda (Hemioniscus), where two pairs of oviducts are found.
The oviducts may have diverticula serving as receptacles for the spermatozoa (in cases where internal impregnation takes place), and may be provided with glands secreting envelopes or shells around the eggs.