644 



taculum seminis , as it does in most other Pol jclads , is continued back- 

 wards and then downwards to open on the ventral surface. 



This appears to be the fourth genus of Polyclads in which a second 

 female aperture is known to occur. In Trigonoponis Lang, and Poly- 

 porus V. Plehn, the apertures are arranged very much as in the Austra- 

 lian form. In Bergendalia Laidlaw, the second aperture leads into 

 the antrum femininum, the main female genital passage thus forming a 

 complete loop. 



The discovery by Herzige of a Polyclad which he calls Laidlmvia^ 

 having a second female aperture situated not on the ventral, but on the 

 dorsal, surface, may help to determine the homologies of the parts. 

 The following may constitute an additional link in the chain of evidence. 



In a form allied to Langs Cryptocelis, also occurring in Port 

 Jackson, the dorsal limb of the vagina opens behind, not on the surface, 

 or into a receptaculum seminis , but into one of the intestinal coeca ; so 

 that there comes to lee, as in Heterocotylean Trematodes, a genito- 

 intestinal canal. This is a condition which, so far as I am aware, 

 has not hitherto been observed in the Polyclads, and it is probably very 

 exceptional in that group. But it is of frequent occurrence in the Hetero- 

 cotylean Trematodes, being present, according to Groto^, in Diplo- 

 zoon, Microcotyle, Axine, Octocotyle, Diclidophora, Oncho- 

 cotyle and Hexacotyle. 



That this passage in the Polyclad is the same as the duct of the 

 receptaculum seminis (or »accessory sac«) which forms the i^osterior 

 termination (lateral and paired in Dlscocelis iigrina, Leptoplana sub- 

 viridiSj and an unnamed Australian form) of the main female genital 

 passage, there can be little room for doubt; and it thus becomes clear that 

 the genito-intestinal passage of the Heterocotylea is the homologue 

 of a passage or receptacle, which, though usually ending blindly, opens 

 in certain cases on the ventral, or the dorsal, surface. This apjaears to 

 me to strengthen the contention, so ably supported by Goto, that the 

 genito-intestinal canal, and not the vagina, of the Heterocotylea is the 

 equivalent of the »Laurer's canal« of the Malacocotylea. 



1 Laidlawia trigonojMra n. gen., n. sp. Zool. Anz. XXIX. 1905. 



2 Studies on the Ectoparasitic Trematodes of Japan. Journ. Coll. Sci. Imp. 

 Univ. of Japan. Vol. VIII. Part. I. 1894. 



