Fig. 476.—A, ovarian egg of a butterfly (Vanessa), surrounded by its follicle; above are the nurse-cells (n. c.), with branching nuclei; g.v, germinal vesicle. B, egg of Dyticus, living; the egg (o.v.) lies between two groups of nutritive cells; the germinal vesicle sends amœboid processes into the dark mass of food-granules.—After Korschelt, from Wilson.
Fig. 477.—A, lower portion of one of the two ovaries of Sphinx ligustri, the four egg-tubes uniting to form the slightly developed calyx (ov). The egg-tubes above contain ripe eggs still surrounded by the follicle; e. c, the empty egg-chamber. Beyond the empty egg-chambers (e. c) are three egg-chambers with ripe eggs and the connecting cord. The whole tube is surrounded by the peritoneal membrane and musculature.—After Korschelt.
3. Comprising ovaries whose ends above the egg-germs contain a well-developed mass of cells functioning as a yolk-forming organ, between whose special elements grow root-like offshoots of nearly ripe egg-cells. (Hemiptera.)
Fig. 478.—Ovary of a beetle, drawn somewhat diagrammatically: o, egg-tube; s, stalk of the same; c, egg-calyx; ov, oviduct.—After Korschelt.
When the egg is ripe the food-chamber disappears because its contents have served for the formation of the egg below it. In Lepidoptera especially, the egg-tubes resemble strings of pearls because most of the numerous eggs ripen simultaneously and are likewise deposited at the same period, which is naturally not the case in those insects whose eggs gradually ripen (Fig. 477). In other cases the egg- or food-compartments are transformed into each other, but only one egg- and one food-compartment can be situated in the same dilatation of the ovarian tube. Finally, there are insects in whose egg-tubes the egg-compartments are arranged in a single row, while the capacious terminal chamber contains a large mass of food-cells.
Egg-cells, nutritive cells, as well as the cells of the follicle epithelium (epithelium of the chambers of the ovarian tubes), originate as similar or homologous elements, division of labor leading to their later differentiation. Only a few of the numerous egg-germs develop into eggs, the rest serving as envelopes and also as food for these few. (Lang.)
In many insects the egg-tubes open into an egg-calyx (Fig. 478, c), in which the ripe eggs collect before passing into the oviduct (ov).
As the result of his investigations on the origin of the cellular elements of the ovaries of insects Korschelt concludes:—