By the telescoping of the 8th and 9th somites the sterna take the position shown in fig. [96]B, and a new cavity, the genital pouch, is formed by invagination. This receives the extremity of the body of the male during copulation, while it serves as a mould in which the egg-capsule is cast during oviposition. Its chitinous lining resembles that of the outer integument. The uterus opens into its anterior end, which is bounded by the 8th sternum; the spermatheca opens into its roof, which is supported by the 9th sternum and the gonapophyses; while its floor is completed by the 7th sternum and the infolded chitinous membrane.
A pair of appendages (anterior gonapophyses) are shown by the development of the parts to belong to the 8th somite. They are slender, irregularly bent, and curved inwards at the tips. A small, forked, chitinous slip connects them with both the 8th and 9th terga, but their principal attachment is to the upper (properly, posterior) edge of the 8th sternum. The anterior gonapophyses expand at their bases into broad horizontal plates, which form part of the roof of the genital pouch.
Two pairs of appendages, belonging to the 9th somite, form the posterior gonapophyses. The outer pair are relatively large, soft, and curved: the inner narrow, hard, and straight.[167]
The anterior gonapophyses form the lower, and the posterior the upper jaw of a forceps, which in many Insects can be protruded beyond the body. Some of the parts are often armed with teeth, and the primary use of the apparatus is to bore holes in earth or wood for the reception of the eggs. Hence the apparatus is often called the ovipositor. It forms a prominent appendage of the abdomen in such Insects as Crickets, Saw-flies, Sirex, and Ichneumons. The sting of the Bee is a peculiar adaptation of the same organ to a very different purpose. In the Cockroach the ovipositor is used to grasp the egg-capsule, while it is being formed, filled with eggs, and hardened; and the notched edge (fig. [5], p. 23) is the imprint of the inner posterior gonapophyses, made while the capsule is still soft. The shape of the parts in the male and female indicates that the ovipositor is passive in copulation, and is then raised to allow access to the spermatheca.
Male Reproductive Organs.
The male reproductive organs of Insects, in spite of very great superficial diversity, are reducible to a common type, which is exemplified by certain Coleoptera. The essential parts are (1) the testes, which in their simplest form are paired, convoluted tubes; more commonly they branch into many tubules or vesiculæ, while they may become consolidated into a single organ; (2) long coiled vasa deferentia, opening into or close to (3) paired vesiculæ seminales, which discharge into (4) the ejaculatory duct, a muscular tube, with chitinous lining, by which the spermatozoa are forcibly expelled. Opening into the vesiculæ seminales, the ejaculatory duct, or by a distinct external orifice, may be found (5) accessory glands, very variable in form, size, and number. More than one set may occur in the same Insect. To these parts, which are rarely deficient, are very often appended an external armature of hooks or claspers.
Fig. 99.—1. Male Organs, ventral view. Ts, testis; VD, vas deferens; DE, ductus ejaculatorius; U, utriculi majores; u, utriculi breviores. 2. Do., dorsal view, showing termination of vasa deferentia. 3. Conglobate gland, and its duct. × 8.
The male Cockroach will be found to agree with this description. It presents, however, two peculiarities which are uncommon, though not unparalleled. In the first place the testes are functional only in the young male. They subsequently shrivel, and are functionally replaced by the vesiculæ seminales and their appendages, where the later transformations of the sperm-cells are effected. The atrophied testes are nevertheless sufficiently large in the adult to be easily made out. Secondly, the accessory glands are numerous, and differ both in function and insertion. Two sets are attached to the vesiculæ seminales, and the fore end of the ejaculatory duct (utriculi majores and breviores); another large conglobate gland opens separately to the exterior. We shall now describe the structure of these parts in more detail.[168]