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Show 312 MR. F. F. LAIDLAW ON THE [Apr. 21, there may be four or even six penes present. In another genus presumably allied to this, viz. Polypostia Bergendal [1], the penes lie in large numbers around the female aperture. The female apparatus is no less remarkable than that of the male. The vagina (ya.) runs forward for some little distance from the aperture, then turns upwards. As it does so, it is twisted into a remarkable spiral coil, making some five complete turns. It then runs backwards, narrows considerably, and soon receives the openings of the two uteri (ut.) on its ventral side. Beyond this point it is continued back as a narrow accessory vesicle (acc.ves.) about as far as the level of the female aperture, when it turns sharply ventralwards and opens to the exterior by the antrum. The only other Polyclads with which I am acquainted that possess a secondary female opening are Trigonoporus of Lang [6] and Polyporus of von Plehn [ii], but in both these cases the second opening is quite distinct from the primary one (the true antrum femininum). The curious spiral twisting of the vagina in the present species is, so far as I know, unparalleled in the order. For the first part of its course, i. e. whilst it is running forwards, the vagina is lined with elongated columnar ciliated cells, the nuclei of which lie near their bases. Outside this epithelium is a thin layer of circular muscle-fibres, and beyond these, in my sections, can be seen a great number of nuclei massed round the vagina, and probably belonging to gland-cells. Where the vagina turns dorsalwards and becomes spirally twisted it has narrowed slightly, but its epithelium retains the characters already mentioned. The muscle-slieath does not follow the individual folds of the spiral, but forms a continuous covering for that part of the duct (PI. XXIII. fig. 6, 7ii.s.). The rest of the terminal female ducts are precisely similar in character to the first part of the vagina, only narrower. There seem to be no special shell-glands present. The genus may be defined as an Acotylean genus in which behind the functional penis a small second penial organ occurs. The accessory vesicle of the female apparatus opens to the exterior through the antrum femininum. Body p>ointed at either end. Marginal eye-spots present ; mouth subcentral. Family L atocestid.e . L aT0CESTUS ARGUS, Sp. 11. Four specimens were collected by Mr. Evans. One of these is labelled " Chocolate-brown above, slightly lighter below." The largest specimen has a total length of about 30 mm. and a breadth of 5 mm. The mouth is 2*5 111111. from the hinder end of the body. This species is proportionately longer than the other member of the genus which I have had an opportunity of examining. Its most striking feature is the presence of a crowded row of eye-spots running completely round the margin of the body. The |