The prostate vesicle (pr) is oval and has a stronger muscular 
wall than the vesicula seminalis, The muscularis is pierced by nu- 
merous duets leading from the extracapsular giand cells. These 
empty their secretion into the lumen of the prostatic vesicle. The 
epithelial lining of this vesicle is also secretory. The large-granular 
quality of the secretion from 
the prostatic giand cells is 
noteworthy. In its reaction to 
eosine it is absolutely normal, 
and thus stains faintly. The 
epithelial lining of the prostate 
vesicle, which contains one- 
third of the thickness of the 
muscular wall, has in addition 
numerous ciliated cells. The 
long cilia reach to the center 
of the lumen of the vesicle, 
and thus exceed the height of 
the epithelial cells. 
Such a thick lining of cilia in the prostatic vesicle, particularly 
when its secretory system has reached its full development, as is 
the case here, is very unusual in Polyclads. On the other hånd, 
before the secretory cells are ready, a dense lining of cilia belongs 
to the epithelial cells. This condition has been treated by me in 
an earlier paper (Bock, 1924, p. 15). The cilia can hardly be 
supposed to aid in the ejaculation of the fluid, for the thick mus¬ 
cular walls of the vesicle are no doubt quite sufficient for this 
purpose. Therefore, I believe the purpose of the cilia is to clean 
up, to produce a water-stream needed for the respiration of the 
tissues, and to distribute the secretion in the lumen of the vesicle. 
The muscular duet that leads from the vesicula seminalis does not 
only pierce the wall of the prostate vesicle, but also projects slightly 
into the lumen as a short thick protuberance. There is, however, 
no division into chambers in this prostate vesicle, as in the case 
of that of Notoplana and Copidoplana, but the cavity of the vesicle 
encircles the protuberance completely. It should be noted that on 
its outer side, that is, the one toward the prostatic lumen, the 
protuberance is covered by an ordinary epithelium without any 
c^v P'' 
Text-fig. 6. Ceratoplana colobocentroti. 
Longitudinal section through genital appa- 
ratus. 66 x, af, antrum feminum; dv, duc- 
tus vaginalis; mu, median uterine duet; p, 
penis; php, pharyngeal pocket; pr, prosta¬ 
tic vesicle; se, seminal canal; vg, vagina ; vs. 
vesicula seminalis. 
