[Illustration: FIG. 86.—Section through a female _Gordius tolosanus_ when the deposition of ova is almost complete. _a_, _b_, _c_, _d_, _e_, and _f_, as in Fig. 84; _g_, egg-sac; _h_, ovary almost empty; _i_, dorsal canal containing eggs; _j_, receptaculum seminis.] In the female larva two similar splits are present; these form the egg-sacs. Posteriorly they end in two short oviducts which open into a uterus, in which fertilisation takes place, and in which the secretion arises which cements the eggs together. In the adult the ovaries and a receptaculum seminis are found, in addition to the organs present in the larva. The ovaries are formed from modifications of the packing tissue; they begin close behind the head, and soon attain such dimensions as to compress the egg-sacs and body-cavity to small slits. After a time the wall between the ovary and the egg-sacs becomes absorbed, and the eggs grow into the latter. In the old females, where the egg sacs are empty, there is a considerable space round the exhausted ovary, into which eggs continue to fall off; there {168}is also a median dorsal canal which contains a few eggs. By this time the wall between the ovary and the egg-sac has again appeared. One of the most interesting points about the female is that, according to Vejdovsky, the ovary is segmented, the cells which form the ova being heaped up in segmentally-arranged masses. This observation, if correct, is almost the only instance of segmentation recorded in the group Nemathelminthes. [Illustration: FIG. 87.—_Nectonema agile_ Verrill. A, The adult. Magnified. (After Fewkes.) B, Longitudinal section through the head. × about 20. (From Bürger.) _a_, Mouth; _b_, circumoesophageal commissure (dorsal); _c_, cell of salivary gland; _d_, septum cutting off head from rest of body; _e_, testis; _f_, ventral cord; _g_, oesophageal cells; _h_, lumen of oesophagus; _i_, cerebral ganglion (ventral).]