e 



PEOF. W. A. HASWELL ON AUSTRALASIAN POLTCLADS. 467 



front of or behind it, tliose in front being the more numerous (about 50), arrano-ed in 

 two parallel groups witli a small space between them. 



The colouring varies somewhat, but is never very pronounced. Some specimens ar 

 almost colourless, but for the light green ramifications of the intestinal c:eca ; but in 

 most there is a faint diffused brown tint due to the presence of minute dots of brown 

 pigment, which are most numerous in the region behind the pharynx. The ventral 

 surface is usually of a light brown colour except in the more central parts, where the 

 pharynx and principal parts of the genital apparatus appear white. One of the most 

 striking features in the aspect of the living animal is the conspicuousness of the 

 intestine and its main branches owing to their presenting tlie appearance of narrow, dark 

 greenish lines on the dorsal aspect of the animal. 



The mouth leads into the pharynx by a fimnel-like passage. The pharynx has about 

 eight to ten pairs of lateral folds and the intestine gives off about the same number of 

 main diverticula. Pharynx and intestine are almost conterminous. 



The two vasa deferentia (PI. 35. fig. 1) join at about the point of union of the anterior 

 and middle tliirds of the penis. The median duct thus formed runs forwards with an 

 almost straight course for some distance ; it is slightly dilated, and its Avail is somewhat 

 thickened, so that it may be regarded as forming a median vesicula seminalis. Further 

 forwards it becomes narrower, and is thrown into a number of coils, in the ordinarv 

 retracted condition of the penis. Eventually, when it reaches a point a little distance 

 in front of the antei-ior end of the penis, it bends sharply round, and runs almost straio-ht 

 back through the axis of the granule-gland papilla, where the ducts of the granule- 

 glands oi)en into it (granule-gland reservoir). 



Tlie penis (figs. 1 & 3) is an elongated muscular cylinder, without spines or otlier 

 special chitinous developments, straight in a well-extended specimen, but more or less 

 bent in a specimen contracted in the direction of the long axis. In front it is quite 

 circular in cross-section ; further back it is more or less compressed. Its walls consist 

 of outer longitudinal and inner circular layers of muscular fibres of approximately equal 

 thickness, and of a layer of columnar epithelium bounding tlie lumen. Surrouudino- it 

 is a thick mass of retiform parenchyma. 



Projecting backwards into the lumen of the penis from its anterior end is the conical 

 papilla (granule-gland papilla) perforated by the terminal part of tlie ejaculatory duct, 

 having the ducts of the granule-glands opening into it. This papilla is formed of an 

 involution of the muscular wall of the penis filled witli the retiform tissue that 

 surrounds it. 



The chief (anterior) female aperture leads into an ootype (fig. 1) of long-oval form 

 with greatly plicated walls. At its anterior end this bends back and passes into the 

 dorsal limb of the vagina. The latter runs backwards near the dorsal surface of the 

 body, and receives from below the unpaired ducts formed by the union of the rio-ht and 

 left uterine ducts. Instead of terminating blindly or expanding into a receptaculum 

 seminis, as in most other Polyclads, the vagina then bends downwards and opens on the 

 ventral surface some little distance behind the main female aperture (PI. 35. figs. 1, 5, & 6). 

 This posterior continuation of the oviduct has a thick, muscular wall ; its epithelium is 



67* 



