162 ^' GOTO, 



median line of the body or otherwise — as formed by the union of the 

 originally paired vaginaa, such as we now meet with in Calicotyle and 

 Oncliocotijle. As a further support to this view it may be mentioned 

 that in Dactylogyrus and Tetmonchus the unpaired vagina, which is 

 present only on one side of the body, opens according to my own 

 observation, into the oviduct in the median line of the body at the 

 same level, as the paired yolk-ducts, just as in Monocotyle. This view 

 appears to me to be more in accordance with the actual state of things 

 than the other, in favour of which hardly a single positive fact can, as 

 it seems to me, be brought forward. 



Let us now turn our attention to that problematic oi'gan, the 

 canalis genito-intesiinalis. This canal is less widely distributed among 

 the . ectoparasitic Trematodes than the vagina : of the genera I have 

 hitherto studied it is present only in Diplozoon, Microcotyle, Axinc] 

 Octocotyle, ■ Diclidophara, Onchocotyle, and Hexacotyle. According to 

 my own observations it seems to be wholly wanting also in the 

 Gyrodactylidae.^^ It always opens at one end into the oviduct near 

 where the latter receives the unpaired yolk-duct — in fact the genito- 

 intestinal canal and the yolk-duct sometimes open opposite, or side by 

 side with, each other ; but usually the two openings are more or 

 less separated from each other ; and in this case that of the genito- 

 intestinal canal is situated in some species nearer and in others farther 

 from- the ovary than that of the yolk-duct. The wall of the genito- 

 intestinal canal presents nothing special except that in some species it 

 presents circular thickenings at stated intervals. 



As a preliminary step to the discussion of the homology of the 



1). I beg to remark here that in my paper on Diplozoon (p. 185) I alluded to the vagina of 

 Dactylogyjiis as being similar to the genito'-intestinal canal. I then suspected that these 

 canals might be homologous with each other ; but on further reflection such a view seems 

 to me untenable. 



