STUDIES ON THE ECT0PARA8ITIC TEEMATODES OP JAPAX. 16^ 



unfortunately it is not in accordance with my observations on 

 a closely allied species {Axine ahermns), in which the Yagina 

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

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

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

 paired to as truly an unpaired condition — Onchocotijle and Calicotijle 

 standing at ojie end of the series and Axine ahermns standing at the 

 other^ In Monocotyle, Tristomum, and Epibdella the external opening 

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

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

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

 or:.right. The latter fact has bsen regarded by Braun as indicating 

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

 one of the originally paired vaginae ; but the relation of things above 

 mentioned in Ilonocotyle, considered together with the evidently close 

 systematic relationship of this genus with Calicotyle, 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 vaginae, and not as Braun supposes by the atrophy 

 of one of them. That the vagina in Octohothrium lanceolatum — a form 

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

 one of the originally paired vagina3 — has been formed by the union of 

 the originally paired vaginae seems to me evident from its exact 

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

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

 Dieckhoffj and in Tristomum and Epihdella 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 



