6. The ovipositor.
The ducts of the sexual glands in Peripatus being transformed nephridia or segmental organs, it has been inferred that this is also the case with those of insects, though, as Lang states, there is a considerable difference in the two cases, as the greater part of the ducts in Peripatus arises out of the ectoderm, while in the Myriopoda and insects they come from the mesoderm; but he adds that in the Annelids the greater part of the nephridial duct is of mesodermal origin.
While in insects there is but a single pair of genital outlets, the serial arrangement of the testicular (Fig. 458) and egg-tubes (Fig. 459) in some Thysanura (Campodea, Japyx, and Lepisma), where the tubes (5 to 7 on each side) open singly one behind the other in segmental succession, indicates that in their ancestors these egg-tubes opened out on different segments situated one behind the other. Each egg-tube independently opens into one of the two oviducts, which extend through the abdomen as straight canals. The two oviducts open externally by a short unpaired terminal portion, which in Machilis is said to be wanting, only the outer aperture of the two oviducts being in this case common to both. In Campodea and in the Collembola the ovaries and testes on each side are simply tubes. It is to be observed that in the young Lepisma Nassonow found that the external openings of the two ejaculatory ducts are paired (Fig. 458 B, ed.).
Fig. 458.—Male genital organs of Thysanura: A, Lepisma in which the testes are segmentally arranged.—After Grassi. B, Lepisma saccharina, young ♂: vd, vas deferens; ed, ejaculatory duct; ga, external appendages,—After Nassonow. C, Machilis, the testis lateral and separate, but not corresponding to the segments. D, Japyx, with an undivided testicular tube on each side; tt, testes; cd, vas deferens; vs, seminal vesicle; ce, ejaculatory duct.—After Grassi, from Perrier.
In the Stylopidæ, also, though this may be the result of adaptation to the singular parasitic habits of the females whose bodies are mostly situated in the abdomen of their host, the ends of the oviducts are formed by the invagination of the integument of the 2d, 3d, and 4th abdominal segments. In the 2d to 5th segments are situated tubes which open in the cavity of the body with funnel-like ends, so that the ducts have a close resemblance to the segmental organs of worms. (Nassonow.)
Fig. 459.—Ovaries of Thysanura: A, of Campodea. B, of Japyx.—After Grassi. C, of Machilis.—After Oudemans, from Sharp.
Fig. 460.—Female genital organs of Lepisma saccharina, adult: ov, ovaries; a, part of the oviduct, corresponding to the calyx of winged insects; od, oviduct; vg, vagina; rs, copulatory pouch; gg, accessory glands; m, muscles; n, nervous cord.—After Nassonow, from Perrier.