J,76 PEOF. W. A. HASWELL OX AUSTEALASIAX POLTCLADS. 



transverse. In the living animal, and to a still more marked degree in preserved 

 specimens, its position is indicated by a rounded elevation on the dorsal surface. There 

 is no enclosino- sheath or sac, the more peripheral muscular fibres passing into the 

 muscular layers of the body-wall or into the layers of parenchyma-muscle that surround 

 the various neighbouring organs (intestinal branches, vasa deferentia, uteri). The 

 muscular fibres are some longitudinal in direction, some circular, some radial, but they 

 are not arranged in any definite layers or zones. At the external apertui'c the muscular 

 mass is quite continuous with the muscular layers of the body-wall. The entire lumen 

 of the penis (distal part of ejaculatory duct) is lined with horny spines or teeth. 

 These (PI. 36. figs. 6 & 7) are largest in the neighbourhood of the external opening, 

 gradually decreasing in size anteriorly. The larger spines are slightly curved, pointed, 

 and have a shape comparable to that of the claw of a bird. In the smaller spines the 

 l)ase is relatively more expanded than in the larger and the distal part more abruptly 

 curved. In the neighbourhood of the opening a process from the underlying tissue 

 projects into the cavity of the spine : further forwards this is not recognizable. 



The female aperture leads into a narrow passage surrounded by a thick mass of 

 parenchyma with numerous muscular fibres. Through this mass run numerous shell- 

 gland ducts, and these perforate the epithelium of the passage in all parts except the 

 part immediately adjacent to the aperture, so that an antrum as distinct from an ootype 

 or shell-gland reservoir can hardly be said to exist. This part of the ootype gives off 

 laterally a number of very short and small diverticula, which have a fairly regular 

 arrangement. "When it approaches near the dorsal surface of the body it expands in the 

 interior of a rounded prominence which projects dorsally in this region a little in front 

 of the female aperture. As it passes forwards it becomes narrow^er and gives off' short 

 irregular diverticula. When it reaches the muscular mass of the penis projecting behind 

 the male aperture it passes to the left, and is continued forwards as a narrow diverticulum 

 (PI. 37. fig. 3) for some distance beyond the male reproductive aperture. Not far from 

 its anterior extremity it receives on its dorsal side the common uterine duct. This 

 unsymmetrical anterior prolongation of the vagina has not a specially developed mus- 

 cular layer, so that it cannot be looked upon as a bursa copulatrix. On the other hand, 

 the ducts of the shell-glands open into it in much greater abundance than into the 

 central part of the ootype itself, and it is best looked upon as a prolongation of the latter. 

 The reflected portion, or dorsal limb of the vagina, produced backwards in most Polyclads 

 beyond the point at which it receives the uterine duct, and frequently leading to a 

 receptaculum seminis, is here entirely absent. 



Clear evidence of the mode of action of the copulatory parts of the reproductive 

 apparatus is afforded by two of my series of sections. In one, a transverse series, there 

 is traceable a long narrow object running obliqviely, on one side only, through the thick 

 mass of tissue refei-red to above as surrounding the vagina, the upper end lying near the 

 lumen of the latter. Traced downw^ards this body is found to run to the ventral surface, 

 where it terminates by perforating the epidermis of the corrugated area in front of the 

 female aperture, projecting slightly on the exterior. In front, between this body and 

 the lumen of the vagina, the tissue is unusually open and spongy, and in the interstice.s 



