13 
increases to a considerable extent, but also because the sperms 
during their passage through the prostate vesicle do not need to 
become mixed with the glandular secretion. In this connection it 
should be mentioned, that in its entire length, thus also the part 
inside the prostate vesicle, this elferent duet from the vesicula semi- 
nalis has a well-developed muscular wall. Therefore, any active 
participation on the part of the prostate vesicle in the ejaculation 
of the sperma is not necessarily needed. From the distal glandless 
end of the prostate vesicle runs the efferent duet as a shaft-like 
continuation through the unusnally elongated narrow penis. 
We now return to the prostate vesicle of Ceratoplana. The effe¬ 
rent duet is mueh longer than the prostate vesicle. The muscular 
covering of the duet is not sharply divided from the muscularis of 
the prostate, which gradually fuses with the muscles of the duet, 
in that the muscle fibres by degrees become grouped in 
rings around the epithelial wall of the duet. The epithelial tube 
begins as a small funnel-shaped projection, pierces the muscular 
wall of the prostate vesicle, and continues through the basal part 
of the penis, surrounded by a thick circular muscle layer, travers- 
ing this organ throughout its entire length; in the meantime the 
muscle layer of the duet gradually diminishes in thickness. 
The penis is unarmed. It is unusually long, and this becomes 
more apparent as its diameter is very small (text-fig. 6 and 7). 
At its base the penis is 60 (.i in diameter, while it gradually tapers 
towards its apex, where its diameter reaches a maximum of only 
S p. In the interior this organ consists of the duet that comes 
from the prostate vesicle. The tissue surrounding it is very feebly 
developed. The muscular sheath of this duet ends, however, at 
about Vs of the distance from the base of the penis to its apex. 
The epithelial lining from the base of the penis to its apex is 
so low that sometimes it can hardly be discerned, and the abso- 
lutely flattened epithelial nuclei are so sparse, that at times they 
are almost indistinguishable. Thus the epithelial lining of the penis 
is very different from the epithelium in the antrum masculinum 
described below. Beneath the epithelium of the penis lies a well- 
developed circular muscle layer with densely arranged fibres. It 
can be traced all the way to the apex. Between this circular muscle 
layer and that of the ductus ejaculatorius is a thin parenchyma 
