15 
base of the copulatory implement. In such a case the antral epithelium 
would need reinforcement. I might here reler to the lining of the 
cirrus in Plarioceridae to aid in the understanding of the purpose 
of these antral cells. But there is, of course, no question of 
homologizing. 
This peculiar organization of the epithelium is limited to the 
two upper thirds of the antrum. It should further be emphasized 
that the cells are very narrow, that they reach a height of 6-8///, and 
that the elongated nuclei occupy the center of the cells. There is a 
distinet limit between these and the extremely thin penis-epithelium. 
In the Wall of the antrum, there is, moreover, a well-developed 
circular muscle layer, traversed by longitudinal muscular fibres. In 
the surrounding parenchymatous tissue numerous coarse protractor 
fibres, as well as bundles of dorso-ventral muscle fibres, oceur. 
The retractor fibres of the copulatory organ are, on the other hånd, 
very feebly developed. 
The male aperture is a little back of the posterior border of 
the pharyngeal pocket. In colob ocentr oti Vs of the space between 
the mouth and the male aperture is oceupied by the pharyngeal 
pocket, only Vs being left for the vesicula seminalis, the prostate 
vesicle, and the penis. In hawaiiensis the male apparatus is more 
removed from the pharyngeal pocket. 
The fe male apparatus. The following description refers in 
the first place to the specimens from Krakatau. 
The female copulatory organ in Ceratoplana differs decidedly 
from that characterizing the genus Stylochoplana, ^hich, as mentioned 
earlier, Ceratoplana in its general organization the most resembles. 
While Stylochoplana without exception possesses a Lang’s glandular 
vesicle, such an organ is here absent. Instead of this, a canal 
runs in a caudal and ventral direction from the entrance of the 
median uterine duet to the female gonopore, and this communi- 
cating canal represents, what I have called the ductus vaginalis 
(Bock, 1913, p. 40 and text-fig. 13). As such it probably corre- 
sponds to the duet leading to Lang’s glandular vesicle (compare 
next chapter). In its general appearance this female genital appa¬ 
ratus agrees more with that which I have described for a Stylochid 
from South Africa, Cryptophallus wahlbergi (Bock, 1913, p. 123, 
text-fig. 13), than with the apparatus of any other Polyclad. 
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