Peripatus

Peripatus, a genus occupying a unique position between myriopods and insects on the one hand and annelids on the other. For, along with the trachæe or air-tubes characteristic of insects, Peripatus has the nephridia or excretory tubes characteristic of the higher worms. The body measures about two inches in length, is shaped like that of a worm or caterpillar, but without external rings, bears numerous (14 to 42) imperfectly-jointed stump-like clawed feet, and has a soft skin, with little of that chitin which is abundant as a cuticular product in other arthropods. The head bears a pair of mobile antennæ, a pair of mandibles in the mouth, and a pair of oral papillæ from which slime oozes. With this Peripatus catches its prey of small insects, &c. The species live in moist places under stones and bark, and are nocturnal in their habits. Professor Sedgwick says that 'the exquisite sensitiveness and constantly changing form of the antennæ, the well-rounded plump body, the eyes set like small diamonds on the side of the head, the delicate feet, and, above all, the rich colouring and velvety texture of the skin all combine to give these animals an aspect of quite exceptional beauty.' There are many remarkable structural features: thus, the ventral nerves are widely separate; the eyes are simple, like those of an annelid; the body-cavity is divided into three longitudinal compartments, from which the cavities of the legs are furthermore distinct. The sexes are separate. The development varies considerably in different species, for the ova may contain a considerable amount of yolk or none at all. In several it has been observed that the cells of the embryo are for a prolonged period indistinctly separate from one another. The embryos develop within the body of the mother-animals; when born they resemble the parents except in size. The distribution is very wide; in South Africa there are four species—e.g. P. capensis, P. balfouri; in New Zealand, P. novæ Zealandiæ; in Queensland, P. leuckartii; in Caracas, P. edwardsii; and others from Demerara, Trinidad, St Vincent, Chili, Quito, &c. The distribution, the structure, and the development of Peripatus all suggest that it is the survivor of an archaic type. The genus is usually dignified as a special class of Arthropods—Prototracheata. See figure under CATERPILLAR; and monograph by A. Sedgwick, Quart. Journ. Micr. Sci., xxviii. (1888).