STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAX. Iß]^ 



unfortunately it is not in accordance with my observations on 

 a closely allied specie.-j ÇAxine ahcrrani), in which the vagina 

 opens, as stated above, into the yolk-dact. If now we eliminate 

 the case of Axine heloncs as requiring further examination, we have 

 in the above mentioned forms a perfect series of vagina3 from a truly 

 paired to as truly an unpaired condition — Oncliocotijle and Calicotijîe 

 standinsr at one end of the series and Axine ahernuis standins" at the 

 other. In Monocotijle, Tri-stomiiiu, and Epihddla the external opening 

 of the vngina is single and is situated on one side of the body. In 

 Monocotijle it opens into the oviduct from the ventral side ; while in 

 Tristomum and EpihdcUa it opens into the yolk-reservoir more to the left 

 or right. The latter fict has been regarded by Braun as indicating 

 the formation of the vagina in these species- by the simple atrophy of 

 one of the originally j^aired vagina? ; but the relation of things above 

 mentioned in Monocotijle, considered together with the evidently close 

 systematic relationship of this genus with Calicot jle, seems to me to 

 point strongly to the view that its unpaired vagina has been formed 

 by the union and subsequent displacement towards one side, of the 

 originally paired vagina^, and not as Braun supposes by the atrophy 

 of one of them. That the vno-iiia in Octohothrinm lanceolatum — a form 

 the single vagina of which Braun regards as due to the atrophy of 

 one of the originally paired vaginœ — has been formed by the union of 

 the originally paired vagina? seems to me evident from its exact 

 similarity to Axine ahermns both in the position of its external open- 

 ing as well as in its relation with the yolk-ducts as described by 

 Dieckhotf ; and in Tristomiun and Epibdella the displacement of the 

 external opening of the vagina towards one side of the body may have 

 entailed a similar displacement of its internal opening. I therefore go 

 one step farther and regard the unpaired vagina — whether its opening 

 be situated on the ventral or on the dorsal side, or whether it be in the 



