28 
the passage of the eggs during shell-formation and meanwhile 
giving the eggs a rotation. It seems very plausible to me that it 
might at the same time act as an effective obstacle to any mass 
of sperma injected into the ductus vaginalis. In this connection I 
might point out, in order to avoid any misunderstanding in the 
future as to the organization of the vagina in the genus Bergen- 
dalia, that very likely the spiral twist only concerns the epithelium 
of the vagina and originates through the formation, by higher epi- 
thelial cells, of a spirally running ridge, and that the thin basement 
membrane of the vagina and the muscular wall are not affected 
by it. This is not mentioned in the descriptions, but I feel that 
I have the right to draw this conclusion from my knowledge of 
the condition in some Stylochids that have not been described 
as yet, and because of the information derived from the outline 
diagrams of sagittal sections of the Bergendalia-sipecies. 
Returning to the function of the ductus vaginalis, there only 
remains to be mentioned that Lang, in his description of this duet 
in Trigonoporiis cephalophtalmus, naturally did not neglect to discuss 
its purpose. On account of its structural development (see Lang’s 
description and diagram), he considers the duet as having 
the function of a pump (p. 315). He denies, with full right, that 
the eggs are emptied by means of it. „Es bleibt also nur die 
Moglichkeit, dass Stoffe von aussen in den Eiergang hineingepumpt 
werden, und da kbnnte man vielleicht vermuthen, dass die Pumpe dazu 
dient. Samenmassen in den Begattungsapparat hinein zu befordern.“ 
He then adds that, from a morphological point of view, the canal re- 
sembles to a certain extent Laurer’s canal in the Trematods and 
the Cestods. However, it seems hardly probable to me that the 
beaded appearance of the duet is due to an adaption to its present 
function, but on the contrary that it is a remnant of the structure of 
the duet from the time when this duet belonged to a Lang’s giand 
vesicle. The ductus vaginalis in Trigonoporus seems less suited 
to copulation. Such a use would certainly have required and 
brought about a change in its appearance. It seems more plaus¬ 
ible that such a method of copulation has not developed as yet, 
but that the vagina in this species still acts as the copulatory organ. 
In such a case the beaded structure retained by the vagina is 
supposed to retard the sperma. Superfluous sperma and the pro- 
