778 PROFESSOR J. STEPHENSON 



about 30 m. The lining epithelium is approximately cubical, or in other cases much 

 flattened, the tube being swollen out into an elongated, thin-walled empty chamber 

 (e.g. right side in fig. 5). 



The atrium (fig. 5) is comparatively small, ovoid in shape, with its long axis 

 vertical, in length 100 m and in breadth 70 m. It is lined by a tall, non-staining 

 epithelium, the cells showing a multitude of minute granules thickly scattered in a 

 clear groundwork. The low cells of the vas deferens are continued some little way 

 into the swelling of the atrium, and then give way abruptly to the columnar cells 

 of the type described. The muscular coat is well marked, especially the layer of 

 circular fibres as seen in a vertical section. The peritoneal investment shows a few 

 small cells ; but there is no " prostate." The lumen may contain spermatozoa, or 

 may be empty. 



The ejaculatory duct is rather shorter than the atrium. It is lined by narrow, 

 closely packed columnar epithelial cells ; it has a well-marked muscular investment, 

 and is surrounded by numerous small peritoneal cells. 



Turning to the female organs which are present in the fully mature animal, the 

 ovisac, which as usual encloses the hinder part of the sperm-sac, is an out-pushing of 

 septum 6/7, which may extend as far back as the hinder end of segment ix. Numerous 

 blood-vessels are seen in sections closely applied to its inner surface (these may, of 

 course, all be the coils of a pair of very tortuous loops). The ovisac does not merely 

 cause a backward bulging of the septa (7/8, 8/9) posterior to it ; these, as seen in 

 longitudinal sections, maintain their transverse direction between the body -wall and 

 ovisac, and fuse intimately with the periphery of the latter. 



The female funnels were not seen in any of the stages. They may possibly be 

 represented by a layer of peritoneal cells which occurs, in one specimen, over a limited 

 area on the anterior face of septum 6/7 near its attachment to the ventral parietes ; these 

 cells are small, and consist of little else than nuclei. Oviducts were not seen at all. 



The spermathecaB (fig. 6) are in segment v. They are a pair of ovoid sacs with 

 their long diameter vertical, and in size measure (maximum) 140 m by 105 m ; they 

 are thus, compared with these organs in some other genera of the Naididse, relatively 

 small. Their epithelial lining is of very irregular height, the cells being of all forms, 

 from a much elongated columnar down to cubical ; in this way are formed a number 

 of irregular projections into the cavity ; the nuclei are peripherally situated. There 

 is a well-marked muscular coat, on the outside of which are a few scattered peritoneal 

 cells (fig. 6, p.c.) ; the nuclei of these latter are not flattened, and the cells may be 

 attached by a comparatively narrow, almost stalk-like, base. The lumen was empty 

 in all the specimens. The duct (fig. 6, d.) is narrow and short ; it is lined by a regular 

 columnar epithelium, and has a strong muscular investment. The aperture is 

 remarkable as being at about the level of the middle of segment v, not, as usual, in 

 furrow 4/5 ; it is at the edge of the clitellum. 



Genital setai (text-fig. l,f) are found in the sixth segment in the fully mature 



