6 Laidlaw, Marine Turbellaria from Torres Straits. 



running from this gland to the penis is joined by the 

 common duct running from the vesiculae seminales. 

 These organs are merely the ends of the vasa differentia, 

 slightly dilated, and supplied with a thin coating of 

 muscle fibres. 



The outer sheath is very thin and consists simply of 

 a few circular fibres ; the muscle wall of the penis consists 

 of circular and diagonal fibres. There are apparently no 

 retractor muscles, but at its distal end the penis, as 

 already stated, comes into contact with the outer sheath. 

 This contact is most pronounced, and continued furthest 

 back from the aperture, on the ventral side. 



Female Organs. These resemble in detail those of 

 P. langii. The aperture leads into a wide muscular cavity 

 from which a large muscular bursa copulatrix runs forward, 

 after first bending to the right, alongside the penis just 

 outside the outer muscular sheath. From the dorsal part 

 of the cavity of the antrum femininum a short narrow 

 duct runs back, receiving the openings of the uteri on 

 either side, then, turning ventral-wards, it widens into a 

 large elongated sac which has non-muscular walls and 

 runs for some distance backwards. This sac I call the 

 receptaculum seminis. Owing to the preservation of the 

 tissues being rather poor, I cannot determine accurately 

 the characters of the epithelium lining the walls of these 

 chambers, but, so far as I can see, it appears precisely 

 similar to that of P. langii. Both the bursa copulatrix 

 (which has its inner walls much folded) and the recepta- 

 culum are filled with dense masses of spermatozoa. 



This species is readily distinguished from P. langii 

 by the possession of dorsal pigment-containing gut 

 diverticula, as well as by the arrangement of the eye-spots. 



The most noteworthy feature presented by species of 

 this genus is the occurrence of the remarkable bursa 



