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larity to it occurs also in, for instance, Plehniidae, PolyposthUdae, 
and Cryptocelidae. The location of the genital pores conforms per- 
fectly with that of the genus Stylochus. Furthermore, the female 
apparatus has a vagina of just the same type. Being here very 
moderately developed, the pharyngeal apparatus has, however, not 
the characterististics of the genera Stylochus, Kaburakia, Parasty- 
lochus, etc.; nor are the intestinal branches densely arranged. But 
these features cannot have a far-reaching importance. Stylochus 
has further well-developed tentacles; here there are merely traces 
of them, as is the case in, for instance, Parastylochus, Cryptophallus, 
Neostylochus, etc. The examination of the male apparatus settled 
definitively that the animal could not be ranked with the genus 
Stylochus, nor with any of the yet described Stylochid-genera. 
The seminiferous system is of a simpler type than that of any 
other Stylochid, seminal vesicles being not distinctly developed. 
But, as in the other members of this family, there is a discrete 
ductus ejaculatorius; a local strengthening of the muscularis of 
each large seminal vesicle shortly before the entrance into the 
ductus ejaculatorius indicates where a false seminal vesicle may 
develop. The penis is large and fleshy, as is often the case in 
the Stylochids Cryptophallus and Parastylochus. The prostatic 
vesicle, the organ par preference having value for the classification 
of the Polyclads, shows unexpected indistinctness. As pointed out 
in the last chapter of this paper, the organ varies considerably in 
the Stylochids. But, as a rule, it is provided with a well-defined 
muscular envelope. In Ilyplana the fibres are loosely arranged, 
and it is impossible to establish a discrete limitation for the mus- 
culature belonging to the vesicle. It intermingles indistinctiy with 
the fibres of the intromittent organ. In the loose grouping of the 
musculature, as well as in the appearance of the low epithelial 
wall of the vesicle and the feeble staining ability of the granular 
secretion, we get resemblances here to conditions met with in the 
Scandinavian Discocelides, whose relationship to the Stylochidae 
cannot be very distant. The distinctness of the muscular envelope 
of the prostatic vesicle of most Stylochids is partly due to the 
the location of it in the parenchyma, even if the dense interlacing 
of the fibres gives it a more pronounced appearance. But, when 
the prostatic vesicle is not removed from the penis, as in Para- 
