In Heliodrilus the blind extremity of the spermatheca is enclosed in a coelomic sac which is in connexion with the sacs envolving the ovaries and oviducts.
In Utricularia bladder-like sacs are formed by a modification of leaflets on the submerged leaves.
The oesophagus leads into a remarkable stomach, plaited like the manyplies of a sheep, and after this the intestine takes a very large number of turns embedded in the yellow liver, until at last it passes between the two renal sacs to the anal papilla.
They are essentially spherical, pear-shaped or oval sacs opening on to the exterior but closed at the coelomic end.
Special sacs developed from the intersegmental septa lodge the developing ova and sperm.
Both male and female gonads consist of more or less lobulated hollow sacs connected with the epidermis by short ducts.
The vesiculae seminales are muscular sacs with a mucous lining which is thrown into a series of delicate net-like folds.
In some cases the ova, after leaving the mouth, are lodged in the oral arms, and undergo the earliest phases of their development in this situation, accumulating in the grooves that continue the angles of the mouth, and bulging the wall of the groove into sacs or pockets.
It is indeed only among the Eudrilidae that the enclosure of the ovaries in septal sacs is at all general.
The mesoblastic somites are paired sacs formed from the anterior lateral portions of the primitive streak (fig.