26 
Herzog (1905) and Zåhony (1907) have treated the Cotylean 
genus Laidlawia possessing a peculiar vesicle with a dorsal end- 
pore, and I will deal with this subject in the publication of the 
German South-Polar expedition, as this interesting Polyclad was 
collected at Kerguelen. However, in no event is such an organ 
homologous to the ductus vaginalis in Åcotylea. 
The function of the ductus vaginalis: No observations 
have been made on the method of copulation in the Polyclads 
possessing a ductus vaginalis. Theoretically one may expect that 
either the vagina or the ductus vaginalis are supposed to receive 
the penis, unless the sperma is directly injected into the tissues. 
The latter method is used by many Cotylean Polyclads, which pos- 
sess a penis armed with a stylet (see Lang, 1884, Bock, 1913). 
The spermatophores can, when such occur, be deposited anywhere 
in the body, Neither of these two methods of hypodermically in- 
jecting the sperma is probably used by Polyclads with a ductus 
vaginalis. An examination of the male apparatus is sufficient to 
show that this is not the case. In passing, it migt be mentioned, 
that Ceratoplana has masses of sperma in the distal ends of the uteri, 
and that the parenchymatous tissue of the body lacks spermatozoa. 
In Copidoplana, with its joint opening for the vagina and the 
antrum masculinum, the use of the ductus vaginalis as a receptacle- 
tube for the penis would make possible, or at least facilitate, 
a simultaneous mutual copulation. The organization of the penis 
seems directly to harmonize with the interpretation that it is in- 
tromitted into the short, narrow ductus vaginalis (Bock, 1913, 
text-fig. 46). As the penis-stylet does not consist of a firm, „chi- 
tinous“ substance, it does not seem suited for hypodermal injections 
nor able to pierce the thick basement membrane of the body. In 
Tripylocelis, which has quite a short and unarmed penis, the median 
uterine duet has such a location that the injected mass of sper¬ 
matozoa can easily make its way further into the uteri. The loca¬ 
tion of this backward-directed median uterine duet, which is very 
unfavourable for the deposit of the eggs, is improved through the 
development of „a process of epithelium, acting as a valve for 
preventing the passage of the eggs backv/ards to the posterior 
female aperture“ (Has well, 1907; the valve is, however, not shown 
on the figure presented). (Of course, it is theoretically possible that 
