16 
The only female gonopore is a short distance back of the male 
aperture (text-fig. 6 and 7), and only separated from it by an inter- 
space 0,15 mm. wide. The body-epithelium around the female aper¬ 
ture lacks glandular cells. From the genital pore a tube leads 
upwards. This soon divides into two, one of which is the direct 
continuation in a dorsal direction and represents the ductus vaginalis 
just mentioned, and the other, homologous to the vagina of Stylo- 
choplana, continuing in a rostral direction. The short joint duet 
to the openings of these canals might be called an antrum femininum 
(af). But, it should particularly be noted that, as regards the 
morphology of the tube and the nature of the wall, there is the 
closest agreement possible between this part — antrum femininum — 
and its direct continuation upwards — ductus vaginalis. Judging from 
the actual conditions, as seen in the series of sections, one would, 
indeed, be entitled to say that the vagina opens into the lower 
part of the ductus vaginalis. The distinetion of an antrum femininum 
then becomes, to a certain extent, theoretical. However, from a 
genetic point of view, the opening of the vagina into the ductus 
vaginalis can be regarded as a secondary feature. Without hesi- 
tation I must assume, that the acquisition of the ductus vaginalis 
took place a great deal later in the history of the genus than the 
development of the typical Polyclad-vagina. Thus, in the beginning, 
the genital pore must have belonged to the vagina. The reasons 
for such an assumption are found in the genus CryptophalluSy which 
shows a more primitive arrangement of the female copulatory 
apparatus. Here the ductus vaginalis opens together with the distal 
end of the vagina (Bock, 1913, text-fig. 13). And such, I believe, 
was the condition at'one time in Qeratoplana. From a theoretical 
point of view it is, however, not quite exeluded to assume that 
L 
the development took place in a different fashion. It might be 
that Ceratoplana has had a special exterior opening for the ductus 
vaginalis, as in the case of Trigonoporus and Bergendalia, and that 
the original female genital pore (= the opening of the vagina) 
has been moved back towards the aperture of the ductus vaginalis 
and upwards along this duet. In my opinion, no real reasons for 
such an assumption exist. It would seem hasty to base such a 
theory merely on the close similarity of the morphology and histo- 
logical development in the „antrum“ and the ductus vaginalis, when 
