On the question of the homology of the canalis genito-intestinalis 

 and all of the vaginal ducts of flatworms, there exists considerable litera- 

 ture in which are expressed the most varied points of view. According to 

 one of them, the vaginal duct of Monogepoidea is homologous to the one in 

 Turbellaria and Cestoidea and to Laurer's canal of Trematoda .whereas the 

 canalis genito-intestinalis of Monogenoidea is similar to the one among 

 Turbellaria. These points of view, with certain alterations, are held by 

 Bresslau (Bresslau, 1928-1933) and Reisinger (Reisinger, 1923) and also 

 Fuhrmann (Fuhrmann, 1928) and a number of other researchers. Others, 

 as for instance Goto (Goto, 1894) and Looss (Looss, 1893), consider that 

 the vagina of Monogenoidea corresponds to the uterus of Cestoidea, where- 

 as the canalis genito-intestinalis c orresponds to Laurer's canal of trema- 

 todes. Finally, a well-known authority of digenetic trematodes, Odhner 

 (Odhner, 1912-1913) supposes that the vaginal duct of Monogenoidea is not 

 homologous among the various species and that the vaginal duct emanating 

 from the ovary represents the true vagina and that the duct emerging from 

 the vitelline reservoir or from the vitelline ducts is a sui generis forma- 

 tion which he designates as the ductus vaginalis. In connection with this, 

 Odhner considers that the ductus genito-intestinalis corresponds only to 

 the true vagina of Monogenoidea and also Laurer's canal of Trematoda. 

 The system of Monogenoidea (see further page 336 ) proposed by Odhner 

 appears to be the result of this point of view. 



We think that the vaginal duct of Cercomeromorphae is a for- 

 mation homologous to that among Turbellaria. Also from our point of view 

 the homology of the canalis genito-intestinalis of Monogenoidea and Tur- p. 72 



bellaria cannot be subjected to any doubt. As for the connparison of the 

 canalis genito-intestinalis and the vaginal duct with Laurer's canal of 

 Trematoda it appears to us more reasonable to compare the latter with 

 the vaginal tract of Cercomeromorphae. The views of Goto and Looss on 

 the homology of the vagina of Monogenoidea and the uterus of Cestoidea do 

 not withstand serious criticism. There is no doubt that it is a result of 

 their being carried away by the convenience of comparison of the inter- 

 relations of the ducts of both groups, but this point of view cannot be recog- 

 nized as correct. Finally the point of view of Odhner has, at first glance, a 

 serious basis; however, in the light of the present level of knowledge of 

 Monogenoidea this view appears erroneous. The fact is that he established 

 two suborders of Monogenoidea (which he accepts as an order). These two 

 suborders, Monopisthocotylinea and Polyopisthocotylinea, differ by the fact 

 that in the second there is a d uctus genito-intestinalis (vagina) and ductus 

 vaginalis, whereas among the former there is only a vagina, however, as 

 Fuhrmann correctly points out, we encounter among the first group of 

 Odhner those relations which this author consider characteristic only for 

 the secnnd group. Thus, for instance among Tristoma there is a ductus 

 v aginalis according to the terminology of Odhner, but there is no canalis 

 g enito-intestinalis. We noticed similar relations among a number of other 

 Capsalidae and among part of Monocotylidae and so forth. Undoubtedly, 



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