Male.—The male organs (Fig. 12) consist of a pair of testes (te), a pair of vesicles (v), vasa deferentia (v.d), and accessory glandular tubules (f). All the above parts lie in the central compartment of the body cavity. In P. capensis the accessory glandular bodies or crural glands of the last (17th) pair of legs are enlarged and prolonged into an elongated tube placed in the lateral compartment of the body cavity (a.g).
Fig. 12.—Male generative organs of Peripatus capensis, viewed from the dorsal surface. (After Balfour.) a.g, Enlarged crural glands of last pair of legs; F.16, 17, last pairs of legs; f, small accessory glandular tubes; p, common duct into which the vasa deferentia open; te, testis; v, seminal vesicle; v.c, nerve-cord; v.d, vas deferens.
The right vas deferens passes under both nerve-cords to join the left, and form the enlarged tube (p), which, passing beneath the nerve-cord of its side, runs to the external orifice. The enlarged terminal portion possesses thick muscular walls, and possibly constitutes a spermatophore maker, as has been shown to be the case in P. N. Zealandiae, by Moseley. In some specimens a different arrangement obtains, in that the left vas deferens passes under both nerve-cords to join the right.
Female.—The ovaries consist of a pair of tubes closely applied together, and continued posteriorly into the oviducts. The oviducts, after a short course, become dilated into the uteruses, which join behind and open to the exterior by a median opening. The ovaries always contain spermatozoa, some of which project through the ovarian wall into the body cavity. Spermatozoa are not found in the uterus and oviducts, and it appears probable that they reach the ovary directly by boring through the skin and traversing the body cavity.[[6]] In the neotropical species there is a globular receptaculum seminis opening by two short ducts close together into the oviduct, and there is a small receptaculum ovorum with extremely thin walls opening into the oviduct by a short duct just in front of the receptaculum seminis. The epithelium of the latter structure is clothed with actively moving cilia. In the New Zealand species there is a receptaculum seminis with two ducts, but the receptacula ovorum has not been seen.
There appear to be present in most, if not all, the legs some accessory glandular structures opening just externally to the nephridia. They are called the crural glands.
DEVELOPMENT.
As stated at the outset, Peripatus is found in three of the great regions, viz. in Africa, in Australasia, and in South America and the West Indies. It is a curious and remarkable fact that although the species found in these various localities are really closely similar, the principal differences relating to the structure of the female generative organs and to the number of the legs, they do differ in the most striking manner in the structure of the ovum and in the early development. In all the Australasian species the egg is large and heavily charged with food-yolk, and is surrounded by a tough membrane. In the Cape species the eggs are smaller, though still of considerable size; the yolk is much less developed, and the egg membrane is thinner though dense. In the neotropical species the egg is minute and almost entirely devoid of yolk. The unsegmented uterine ovum of P. Novae-Zealandiae measures 1.5 mm. in length by .8 mm. in breadth; that of P. capensis is .56 mm. in length; and that of P. Trinidadensis .04 mm. in diameter. In correspondence with these differences in the ovum there are differences in the early development, though the later stages are closely similar.
Fig. 13.—A series of embryos of P. capensis. The hind end of embryos B, C, D is uppermost in the figures, the primitive streak is the white patch behind the blastopore. (After Sedgwick.) A, Gastrula stage, ventral view, showing blastopore. B, Older gastrula stage, ventral view, showing elongated blastopore and primitive streak. C, Ventral view of embryo with three pairs of mesoblastic somites, dumb-bell-shaped blastopore and primitive streak. D, Ventral view of embryo, in which the blastopore has completely closed in its middle portion, and given rise to two openings, the embryonic mouth and anus. The anterior pair of somites have moved to the front end of the body, and the primitive groove has appeared on the primitive streak. E, Side view of embryo, in which the hind end of the body has begun to elongate in a spiral manner, and in which the appendages have begun. At, antenna; d, dorsal projection; p.s, preoral somite. F, Ventral view of head of embryo intermediate between E and G. The cerebral grooves are wide and shallow. The lips have appeared, and have extended behind the openings of the salivary glands, but have not yet joined in the middle line. At, antennae; c.g, cerebral groove; j, jaws; j.s, swelling at base of jaws; L, lips; M, mouth; or.p, oral papillae; o.s, opening of salivary gland. G, Side view of older embryo with the full number of appendages, to show the position in which the embryos lie in the uterus.