STtfDIIilS ON THE ECTOPARASITIC TREMATODES OF JAPAX. 163 



canalis genito-intestinalis we must consider that of tlie vagina of the 

 Cestodes. 



Until quite recently the vagina of the Cestodes appears to have 

 been generally regarded as homologous with the Laurer's canal 

 of the distomes ; but a careful examinatioa of this view convinces 

 me that hardly a single positive proof can be cited in its favour, 

 and that it is grounded on a mistaken estimate of the analogy 

 (as opposed to homology) that has been supposed to exist between 

 the two organs. Looss'' has however recently shown that the 

 vagina of the Cestodes is to be regarded as the homologue of th& 

 uterus of the Trematodes. On my part I entirely agree with him on' 

 this point, and will briefly recapitulate the reasons that led me to this 

 conclusion, even before I had read Looss' paper. 



If we cast a glance on the genital organs of the Plathelminthes 

 (the Nemertinei excepted), we find that in all the three classes two 

 ducts open to the exterior, i. e., to the morphologically external surface 

 of the body, near each other. One of them is the vas deferens ; the 

 other is in Turbellaria the eiFerent duct of the ovary, while in the 

 Cestodes and Trematodes it is called respectively the vagina and 

 the uterus ; but in these classes it is likewise the direct con- 

 tinuation of the oviduct. In Canjopliyllceus tuba, indeed, the uterus 

 opens, according to Monticelli'^ side by side with the vagina, 

 and in C. viutabilis, according to Will'\ it unites with the vagina, so 

 that in this genus the uterus and not the vagina corresponds in the 

 position of its external opening to the uterus of the Trematodes. But 

 the uterine opening seems to be very unstable in its position in the 

 Cestodes ; for in Ainpliilina it is near the anterior end of the body, 



1). Looss. — I. c. 



2). Montioelli — Appunti sui Cestodaria. p. 5. 



3). Heinrich Will — Anatomie von CaryophyUseus mutabilis. Zeitschr. f. wiss. Zool. 

 Bd. 56. 1893. Taf. II. &g. 17 



