Fig. 96.—Diagram to show the theoretical (upper figure) and actual position of the hinder abdominal sterna in the female Cockroach. U, uterus; s, spermatheca. The nerve-cord is introduced into both figures.
The external reproductive organs of the female Cockroach belong to the 7th, 8th, and 9th somites. The 7th sternum is incompletely divided into anterior and posterior sections, and the posterior section is split into lateral halves. These are joined by a flexible membrane, which admits of the wide separation of the halves, when copulation or the passage of the large egg-capsule renders it necessary. The vertical faces of the membrane, which are pressed together when the parts are at rest, are stiffened by chitinous thickenings.
Fig. 97.—Hinder end of abdomen of female Cockroach. In the upper figure the halves of the 7th sternum are closed; in the lower figure they are open.
If the succeeding sterna retained their proper place, as they do in some Orthoptera (e.g., the Mole Cricket), the 8th and 9th sterna would project beyond the 7th, while the rectum would open beneath the last tergum, and the uterus between the 8th and 9th sterna. In the adult female Cockroach, however, the 8th and 9th somites are telescoped into the 7th, and completely hidden by it. Their terga are reduced to narrow bands. The 8th sternum forms a semi-transparent plate which slopes downwards and backwards, and is pierced by a vertical slit, the outlet of the uterus. The upper edge of this sternum is hinged upon the projecting basis of the anterior gonapophyses (to be described immediately), and the parts form a kind of spring joint, ordinarily closed, but capable of being opened wide upon occasion. The 9th sternum is a small median crescentic plate, distinct from the 8th; it supports the spermatheca, whose duct traverses an oval plate which projects from the fore-edge of the sternum.
Fig. 98.—External Reproductive Organs of Female. T8, &c., terga; S7, &c., sterna; G, anterior gonapophysis; G′, its base; g, posterior gonapophyses; Od, oviduct; sp, spermatheca; R, rectum. The upper figure shows the parts in oblique profile; the left lower figure is an oblique view from before of the outlet of the uterus, the anterior gonapophyses being cut short; the right lower figure shows the gonapophyses. Arrows indicate the outlet of the oviduct and uterus.