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Show 1903.] FROM ZANZIBAR AND BRITISH EAST AFRICA. 105 the two vasa deferentia at its hinder end. Its walls are thin and consist of circular muscle-fibres. The resemblance existing between these organs of Bisparoplana and those of Planocera and Paraplanocera is so great, that w e are compelled to assume a close relationship between these genera. In the shape of the penis Bisparoplana approaches rather the latter genus, whilst in possessing a single vesicula seminalis it approximates rather to the former. Female apparatus.-The antrum femininum is large and rather elongated. The vagina, after running forward to receive the separate openings of the uteri, is continued back as the accessory vesicle which ends blindly after making a second turn forwards, ventral to the first part of its course. The shell-glands open into the accessory vesicle. The inclusion of this species in the Planoceridse will necessitate an alteration of the definition of that family. I do not attempt to offer a new definition in the present paper, since it is necessary to have information concerning the anatomy of a large number of species the internal structure of which but little is known, before any useful modification of Lang's definition can be suggested. However, it is permissible to point out here that the discovery of such a form as Bisparoplana indicates, I think forcibly, not only that in the future our definition of the Planocerida? will have to be altered, but also that the Leptoplanidae may be a polyphyletic family. The genus Bisparoplana may be defined as follows:-An elongated form, not provided with tentacles; the eyes arranged in two lines over the brain. Mouth a little in front of the middle of the body. Penis cylindrical, armed with chitinous spines resembling those of Planocera; a well-developed prostate and single large vesicula seminalis present. Female ducts simple, a small accessory vesicle present. STYLOCHUS ZANZIBARICUS, sp. nov. Labelled " s.s. Juba." A small, rather elongate form. Length 10 mm. Breadth 4 ,, Tentacles from anterior end 2'5 ,, "Mouth" „ „ 7 „ Genital openings from hinder end ... "5 „ No note as to colour, but to judge from the single spirit-specimen, this is mottled reddish-brown and yellow on the dorsal surface; the ventral surface is uniform greyish yellow. The eye-spots are found on and about the base of the tentacles and on the anterior margin, where they are of moderate size (see text-fig. 5, p. 106). I have not found any definite group of brain-eyes. |