166 s. Gofo. 



degree of plausibility for the Viigina of the Monogenea, as will be 

 apparent from the descriptions already given and a comparison of my" 

 figures ; while, on the other hand, it holds very well for the genito- 

 intestinal canal, the wall of which is, as already mentioned, charac- 

 terised in some species by having circular thickenings exactly similar 

 to those of the oviduct; and Dieckhoff'^ has even expressed the 

 view that the canal may perhaps be a rudimentary (abortive?) oviduct. 

 Add to these the considerations that the vaginas of the Monogenea are 

 clearly seen to have been originally paired, while on the other hand 

 Ave have no trace of the paired condition of the Laurer's canal and of 

 the genito-intestinal canal; that the latter was regarded as, and 

 called by some writers, the Laurer's canal so long as they believed it 

 to open to the exterior (Taschenberg in Oncliocotyle) or to be in 

 direct continuation with the vas deferens of the other individual 

 (Zeller in Diplozooii); and finally that the genito-intestinal canal, like 

 the Laurer's, " puo apprirsi, o nell'ovidotto, o nel ricettacolo seminale 

 (as in Hexacotyle) o, insieme a questo, nell'ovidotto," the evidences 

 in favour of my view — that the genito-intestinal and the 

 Laurer's canal are homologous with each other — seem to 

 me to be very strong, much stronger than the evidences that can be 

 brought forward in favour of the other view, which appears far from 

 being " irrefutable." 



I have said above that we have no evidence of the fact that the 

 genito-intestinal canal was originally paired. There are, however, 

 some statements that require consideration in this respect. According 

 to Zeller ^^ the genito-intestinal canal is, in Folystomum integerrimum , 

 situated indifferently on the left or on the right side of the body, 



1). Dieckhoff— ;. c. p. 248. 



2). Zeller— Weiterer Beitrag zur Kermfcniss der Polystomen. Zeitsohr. f. wiss. Zool., 

 Bd. 27, 1876. p. 245. 



