IJ2 s. GOTO. 



menon. For, according to the view of Monticelli and Pint ner, 

 the genito-intestinal canal is " un adattamento speciale " in the Mono- 

 genea, while according to that of Looss the vagina? of the same are 

 " Bildungen sui generis" — i.e., in logical language residual pheno- 

 mena. And as to the genito-intestinal canal being a special adapta- 

 tion in certain members of the ]\lonogenea, it is exceedingly difficult 

 to see how and from what necessity such a canal could have been 

 specially developed in a limited number of forms, while totally want- 

 in"" in others. Whereas, if we regard the cannl as in process of 

 abortion, we meet with no difficulty, and the various facts appear to 

 me capable of being brought into harmony with each other. Accord- 

 in<T to niv view, then, the Trematodes and the Cestodes are to be 

 derived phylogenetically from a form which — adopting the termino- 

 loo-y applicable at present only to the Monogenea — possessed the 

 paired vagina?, the uterus, and another duct, the homologue of the 

 canalis gcnito-intestinaUs. In saying this, however, it should be observ- 

 ed that I by no means assert these organs to have had in the suppos- 

 ed ancestral form the same function as they have now in either of its 

 descendants. 



As an addendum to the above discussion I beg to make just one 

 short remark on the vagina of Diplozoon. In my paper on Dipl. 

 Nipponiciim, I have described the vas deferens of one individual as 

 standing in direct connection with the yolk-duct of the other. In 

 doing so I stated merely what I could directly observe ; for in my 

 sections I could not distinguish the vagina from the vas deferens. It 

 is true that the terminal portion of what I then considered the vas 

 deferens was exceedingly small, but this portion was not set off by 

 any demarcation from the proximal portion. I fully admit, how- 

 ever, the justness of Pin tn er' s '^ criticism on this point. I have 



1). Pintner— Nochmals über den Begattungsakt der parasiLischen Platheluiinthen. Cen- 

 tralbt. f. Bakter. u. Parasitenk., Bd. 9, 1891, Xo. 22. 



