THE MARINE TURBELLARIA. 287 



rather near the ventral surface. As it approaches the vagina it makes a sharp turn up and 

 the appearance of the epithelium changes; circular muscle fibres make their appearance, and, 

 after receiving the uterine openings, the organ is continued forward as the vagina, the epi- 

 thelium here consisting of a short, columnar, ciliated facies. The nuclei are homogeneous 

 and darkly-staining; the protoplasm is hyaline. The bursa copulatrix extends forward as far 

 as the front end of the male apparatus. Its inner walls are much folded and lined with 

 cubical non-ciliated epithelium. Outside this it has moderately thick muscular walls composed 

 of circular fibres. The undescribed species from Rotuma, to which I have already referred, 

 bears a strong resemblance so far as the female apparatus is concerned to PI. langii. In it 

 the receptaculum seminis is crowded with spermatozoa. 



Male apparatus. The outer sheath consists in this species of circular fibres only. 

 From the antrum masculinum for about a quarter of its length, which is roughly a millimetre, 

 it is continuous with the intrinsic muscular wall of the penis, and traversed by scattered, 

 radial fibres running fi-om the latter. 



After this a split appears between it and the intrinsic muscles of the penis, leaving a 

 space round the latter. At the upper anterior end the prostate as in the other Planocera 

 lies in close contact with the outer sheath. The few muscle-fibres surrounding the prostate 

 do not seem to be derived from the outer sheath. Lastly the sheath is pierced at two 

 points by the ducts running to the penis from the vesiculae seminales. 



The penis is approximately a millimetre in length. It is a cylindrical, tube-like organ, 

 its lumen lined with chitinous spines, which are a little hooked and not very thickly set. 

 The diameter is roughly equal throughout its entire length. The muscular wall consists of 

 a well-defined, rather thick layer of circular fibres crossed by radial fibres. The penis is con- 

 tinued right up to the level of the prostate, which communicates with it by a short, wide, 

 muscular duct, opening into it at the same point as do the ducts from the vesiculae. 



At a point about one-third of the total length of the penis fi-om the male aperture 

 the chitinous spines are interrupted by the appearance of two curious folds of the imier 

 wall (PI. XV. Fig. 13, pL). These folds are margined with chitinous material. It is possible 

 that they may be to some extent comparable to the chitinous hooks or collar of PL armata, 

 but their function is quite unknown to me. Behind them the spines are continued again 

 up to the level of the opening of the prostate duct. As already stated each of the vasa 

 deferentia is dilated before entering the outer sheath to form a vesieula seminalis, and the 

 dilated part has muscular walls composed of circular fibres. The ducts running' fi-om the 

 vesiculae to the penis are also muscular. 



Before passing to consider the species belonging to the next family I may briefly notice the 

 presence of a large Planoceroid represented by a single damaged specimen in the collection, 

 which I am not able to describe. Its total length is probably about 45 mm. A pair of 

 dorsal tentacles are visible. It is perhaps a Stylochoplana. I could only find indications of 

 a single genital aperture, the genital organs being quite immature. 



II. Family Leptoplanidae. 



3. Leptoplana pardalis, sp. n. (PI. XIV. fig. 9, and PI. XV. fig. 14). 



Several specimens from the reef, Goidu, Goifurfehendu Atoll, and from Minikoi, Laccadive 

 Group. 



G. 37 



