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. {20}[Illustration: 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.]