STUDIES ON THE ECTOPARA.SITIC TKEMATODES OF JAPAN. 169 



phologically to the vagina of other tapeworms and is homologous 

 with it. What then is the blind vagina? My answer is that it is the 

 homologue of the genito-intestinal canal of the Monogenea and there- 

 fore of the Laurer's canal. What has struck me as a remarkable 

 coincidence is that all these organs bear a decidedly abortive character. 

 That the Laurer's and the genito-intestinal canal appear to be in the 

 process of gradual disappearance has been already explained, and will, 

 I think, be admitted by most persons ; and the blind vagina of 

 Ampliilina appears to me as unmistakably abortive — the very fact 

 of its being blind and its total absence in the nearly related form 

 Canjopliyllccus speaking strongly for this view. Then, it bears at its 

 beginning a receptaculiim semiiiis just like Laurer's canal in most of the 

 distomes or the genito-intestinal canal in some Monogenea ( Hcxacotijle). 

 Again, if, as I have explained above, the receptacidum vitelli of Aspido- 

 gaster is homologous with the Laurer's canal, we have another simi- 

 larity between it and the accessoi*y vagina of Ampliiliim, in their both 

 ending blindly. Lastly, the relation of this vagina to the oviduct is 

 exactly the same as that of the Laurer's or of the genito-intestinal canal 

 to the oviduct in the Trematodes, I therefore believe them all homolo- 

 gous with one another. The blind ending of the canal in Ampliilina 

 may have been brought about by a simple abortion of its terminal por- 

 tion, as in Aspidogaster, or by a total disappearance of the alimentary 

 canal, with whicji it had baen connected as it now is in many species 

 of Monogenea. 



I am now going to propound the opinion which may seem to 

 many exceedingly heterodox, that the uterus of the Cestodes is 

 homologous with the vagina of the monogenetic Trematodes. But to 

 make my arguments properly appreciated it is necessary to explain 

 my conception of the relations of the various genital ducts in the 

 Cestodes. In these the uterus has, I believe; usually been regarded as 



