Among the winged insects the reproductive organs of the cricket (Fig. 466) are perhaps as simple as any. The testes are separate, and the vasa deferentia very long. The seminal vesicles bear numerous large and short utricles (utriculi majores and breviores), the penis being simple and dilated at the end; while in Phyllodromia germanica the testes are functional throughout life, and consist of four lobes each. In the common cockroach (P. orientalis) (Fig. 461) the testes are functional only in the young male; they afterwards shrivel and are functionally replaced by the vesiculæ seminales and their appendages, when the later transformations of the sperm-cells are effected. The accessory glands are numerous and differ both in function and insertion. Two sets of these glands (utriculi majores and breviores) are attached to the vesiculæ seminales and the fore end of the ejaculatory duct, while another appendage, called by Miall and Denny the conglobate gland, opens separately on the exterior upon a double hook, which forms a part of the external genital armature. The so-called penis is long, slender, and dilated at the end, but is not perforated.
Fig. 461.—A, male organs of the cockroach, ventral view: Ts, testis; VD, vas deferens; DE, ductus ejaculatorius; U, utriculi majores; u, utriculi breviores; 2, dorsal view; 3, CG, conglobate gland and its duct. B, male organs, side view: A, titillator; B, penis; other letters as in A.—After Miall and Denny.
In the locusts (Acrydiidæ) the testes are, unlike those of most other Orthoptera, closely united to each other so as to form a single mass of tubular glands into which penetrate both simple and dilated tracheæ; the entire mass is situated in the 3d, 4th, and 5th abdominal segments, and above the intestine. The anterior end of the testicular mass is rounded and held in place by a broad, thin band, one on each side; two similar bands are situated a little behind the middle of the mass. From the under side, and a little in advance of the middle of the mass, two straight small ducts, as long as the testicular mass, pass obliquely to the sides of the body, at the posterior end of the 7th segment of the abdomen; these are the vasa deferentia. Each vas deferens, with its mate, forms a convoluted mass of tubes, comprising twenty folded bundles (epididymis of Dufour), and two single, long, convoluted tubes, the vesiculæ seminales, which are lobed in the 6th and 7th segments of the abdomen. The two vesiculæ unite over the 5th abdominal ganglion, forming a thick, very short canal (ductus ejaculatorius), which passes into a large spherical muscular mass (præputium), behind which is the large intromittent organ (penis), which forms a short chitinous cylinder, quite complicated in structure, being armed with hooks and projections and affording excellent specific characters. It can be seen in place without dissection by drawing back the orbicular convex piece called the velum penis.
In the Hymenoptera the reproductive system is quite simple, as seen in Fig. 462.
Fig. 462.—Male organs of saw-fly (Athalia centifoliæ): a, a, testes; b, b, epididymis; c, d, vas deferentia; e, vesiculæ seminales; f, ductus ejaculatorius; h, penis (see also p. 180).—After Newport.
The general shape and relations of the female reproductive organs are seen in Fig. 298, of the locust (Acrydiidæ). The ovaries consist of two large bundles of tubes, each bundle tied to the other by slight bands, with air-sacs and tracheæ ramifying among them. These tubes extend along the intestine, passing into the prothorax. The ovarian tubes opening into the oviducts unite to form the vagina, which lies on the floor of the abdomen. (In the cockroach the vagina has a muscular wall and chitinous lining.) Above the opening of the duct, and directly communicating with it, is the copulatory pouch (bursa copulatrix), a capacious pocket lined within with several narrow, longitudinal, chitinous bands. Behind the bursa copulatrix lies, partly resting under the fifth abdominal ganglion, the sebific, cement, or colleterial gland (colleterium; compare Fig. 299, sb), which is flattened, pear-shaped, a little over half as long as a ripe egg of the same insect. From the under side, a little in advance of the middle, arises the sebific duct, which, after making three tight coils next to the ganglion, passes back and empties into the upper side of the bursa copulatrix, dilating slightly before its junction with the latter.
The most primitive type of reproductive organs observed in insects is that of the young Lepisma and the Ephemeridæ, in which the outlets of the oviducts and of the vasa deferentia respectively are double or paired, showing that insects have probably inherited these structures from the segmental organs of their vermian ancestors.
Réaumur had already observed the process of oviposition and seen that the female Ephemera had two openings near the end of the “6th” abdominal segment, from which he saw two masses of eggs pass out at a time (Fig. 463). Eaton afterwards (1871) referred to the oviducts as terminating between the 7th and 8th segments of the abdomen, and after him Joly; but for a detailed monograph on the subject we are indebted to Palmén. He found that the outlets of the sexual glands are paired, not only in the larvæ of all stages, but also in the imagines, and in both sexes. In the males the vasa deferentia pass on the ventral side of the 9th segment through two external appendages, both reproductive organs, at whose tips or sides the openings are situated. In the larvæ the female openings are not formed until after the last moult. In the females the two oviducts open on the ventral side of the hind-body between the 7th and 8th segments.