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adaptation for the prolongation of the copulatory implement. Semi- 
nal vesicles represent a late acquirement for the accumulation and 
simultaneous ejaculation of a larger mass of sperma. In several 
Acotyleans they are not yet developed. 
The interpretation that the seminiferous system has established 
connection with previously independent weapons of glandular nature 
which thus have been transformed into copulatory organs is not a 
new problem but for Polyclads has been vindicated by Lang 
(regarding Ånonymus) and Bergendal. It is also in accordance with 
ideas developed by v. Graff. His starting point has been the Åcoela 
and their poison weapon. However, I find it not necessary to 
accept his hypothesis of the Åcoela as the ancestors of other Tur- 
bellaria and thus also of the Polycladida. As I shall describe in 
another paper, glandular weapons may also occur in the Polyclads 
fully independently of the genital system. Graff has treated the 
„muskuløse Drusenorgane“ of the Triclads in „Bronn“ and enumerates 
a number of examples. With the exception of one, Polycelis cornuta,’^) 
all these have them in atrium genitale. Several Polyclads, for instance 
Paraplanocera disens and Boninia mirabilis^ have from one to many 
glandular organs in antrum masculinum. In this connection Disco- 
celis might be recorded, though not enough appreciated by Lang, 
as having them of simple type. 
After this short introduction, which was necessary in order to 
get an understanding of how the male copulatory organ has to be 
interpreted, we return to the Stylochids. If it is correct — and 
everything seems to speak for this theory — that the prostatic 
organ is the primitive element in the male apparatus of the Poly¬ 
clads, it is at once clear that with respect to its male apparatus 
Enterogonia is a degenerated type, the vesicula granulorum appe- 
ars here only as a little diverticle of the ductus ejaculatorius, a 
pitiable remnant from better days. A step further in the reduction 
of this diverticle would have brought about its complete disappear- 
ance and it would consequently have been nearly impossible to 
recognize and definitively prove that this male apparatus has origin- 
ated from a Stylochidean type. I regard the successful interpre¬ 
tation of Enterogonia as one of the best results obtained from Dr. 
*) This species deviates from P. nigra through having the organs in 
question in a special pocket shortly behind the genital pore. 
