PliOE. AV. A. HA SWELL ON AUSTRALASIAN POLTCLADS. 109 



vesicula. Prostate-giand reservoir situated in the course of the ejaculatory duct. No 

 bursa copulatrix. Vagina continued baclvAvards to open on the ventral surface by the 

 second female aperture. 



Tiie discovery by Ilerzig (9) of a Polyclad (named by him Laidlawla) which has a 

 second female aperture situated not on the ventral but on the dorsal side, may be 

 regarded as of some importance, as it may help us towards a determination of the homo- 

 logies of the parts. A correspondence with the Trematode " canal of Laurer " and with 

 the Cestode " vagina " and recej^taculum seminis obviously suggests itself. Bergendal 

 lias recently described a Triclad Avith a second female aperture, and I have shown that 

 such an opening (dorsally situated) occurs in the Acoela, so that an arrangement of this 

 kind would seem to be very widespread in the Platodes. In all such cases the object of 

 tlie arrangement is, most probably, to enable fresh supplies of spermatozoa to be taken 

 in without any interference wMth the passage outwards of the fertihzed ova. But it may 

 be that in some cases tlie canal has lost its function, though still persisting, or may have 

 l)ecome adapted to other uses. 



DiPLOSOLENiA JOHNSTONI, n. g., n. sp. (Plate 36. hgs. 1 & 2.) 



This is a very large Polyclad, one preserved specimen measuring 6 cm. in length and 

 cm. in breadth. The mouth is somewhat in front of the middle — in the thml 

 centimetre. The reproductive apertures are situated close together (or combined in one) 

 at the junction of the fourth and lifth centimetres. The tentacles are rather long and 

 of conical shape : they are placed a little behind the junction of the first and second 

 centimetres. The eyes are in two very compact groups, each comprising about 30, at 

 the bases of the tentacles, and two longitudinally extended less comjmct groups between 

 them, each of these also comprising about 30. Tlie dorsal surface is almost black, with 

 a narrow light margin. 



The pharynx has about twelve pairs of lateral folds. 



In two of the specimens, which have the j^iinis exserted and a considerable length of 

 the stylet projecting, the male and female apertures are separated by a distinct interval. 

 On the otlier hand, in the specimens with the penis retracted the parts of the body-wall 

 in the neighbouvhood of the apertures become involuted to form a kind of common 

 antrum having but a single external opening. 



The ventral part of the vagina is a long narrow passage the lumen of which has a 

 triangular cross-section in ti\e greater jjart of its extent. Its muscular investment is 

 thin, and it has an epithelium of long narrow cells. In the posterior part of its extent, 

 in the specimen sectioned, the lumen is lilled entirely with the shell-gland secretion 

 which completely saturates the epithelium. Further forwards numerous spermatozoa 

 are also present ; but in the anterior i)art of the passage these disappear and the lunaen 

 is filled with the shell-gland secretion. 



The vagina becomes bent liack sharply on itself, the dorsal liuib running Ijack to a 

 point just over the base of the (exserted) stylet, where it bifurcates to form the ducts 

 of the two lateral receptacula seminis which run almost transversely outwards (fig. 2). 

 This dorsal part of the vagina is a narrow cylindrical tube, with an epithelium of 



