STUDIES OX THE ECTOPARASITIC TREMATODES OF JAPAN. IQJ 



always, however, opposite the side at which the ovary is situated. In 

 Polystomum ocellatuin, again, the canal is described and figured by 

 Dieckhoff '^ as lying on the left side ; and in Sphymmira Osleri it is 

 figured by Wright and Macallum.^^ as lying likewise on the left 

 side. On the contrary, in all the species I have examined, the canal 

 is situated, as already mentioned, on the right side of the body ; and 

 this led me to ask Prof. Ijima whether he had not observed such a 

 position of the canal. He very kindly examined the serial sections of 

 two individuals of Polystomum ocellatum which he had at hand, and he 

 has informed me that the canal is situated on the right side in both. 

 This perhaps shows the necessity of a reexamination of the statements 

 to the contrary, effect j but. as this is at .present impossible for me to 

 do, I shall only remark that they do not oblige us to regard the genito- 

 intestinal canal as having been originally paired, any more than the 

 varied position of the common genital pore in Tcenia compels us 

 to infer its having been paired originally. 



It will be remembered that one ot the reasons that have led 

 Monticelli to assert the homology of the Laurer'a canal with the 

 vagina of the Monogenea is that " nei digenetici non vi e altra parte 

 dell'apparechio genitale che possa reguardarsi come una vagina." 

 But if instead of starting with the assumption that a morphological 

 equivalent of the vagina of the Monogenea must exist in the 

 Digenea, he had put the question simply as we have done, he 

 would have been led not to make the positive statement we have 

 quoted, denying all homology of the genito-intestinal canal with 

 the Laurer's. 



In my paper on Dlplozoon^^ I expressed the opinion that the reeep- 



1). Dieckhoff— i. c. p. 250. 



2). I. e. 



3). Goto-i. c. p. 184. 



