170 s. GOTO. 



the direct continuation of the oviduct, and the vagina as an accessory 

 duct. From a physio] og'i cal point of view this conception is quite 

 correct — the ovum in fact passes from the ovary into the uterus. 

 Ihit, as I have ah'eady explained above, this mode of conception seems 

 to me morpliologically not correct. I regard the vagina as the direct 

 continuation of tlie oviduct, and both the yolk-duct and the uterus as 

 accessory ducts opening into the former. And in accordance with 

 this view I. regard that portion of the genital duct in Tœiiia and 

 CartjophjUœns^^ (PI. XXYII, lîgs. 5 & G) which lies between the 

 befrinnin"' of the vaiiina and the beo'innino- of the uterus as the yolk- 

 ihict. It may be ol)jectcd tliat the position of the shell-glands, which 

 are in otlier forms always situated around a portion of the oviduct, is 

 against such a view. Jhit the shell-glands being evidently a special 

 physicjlogical provision, I believe that their position must not be regard- 

 ed as constant; in fact, they do vary considerably in position even 

 among the monogenetic Trematodes; and if they can be displaced in 

 one direction there seems to me tobe no re:json why they can not be dis- 

 placed in another, provided only that there be a physiological necessity 

 for it or an advantage u'ained thereby. I therefore believe that in 

 Ta'iiia the shell-glands have shifted position from the initial portion of 

 the vagina (or its homologue, as in the Trematodes) towards the 

 uterus, in consecjuence of the changed functions of these two canals 

 (i.e., their respective homologues) in tlie Trematodes and the Cestodes — 

 assuming for the time being that the monogenetic Trematodes present 

 a more primitive state of things. This granted, let us compare the 

 uterus of the Cestodes with the vagina of the monogenetic Trematodes. 

 The most strikini>- difference between these two structures is that 

 one of them is clearly seen to have l)8en originally paired, while the 



1). Cf. Monticelli's "Appunti [etc." and Will's " Caryopliyllseus mutabilis" (PI. II» 

 fig. 17). 



