27 
this same valve might be an obstacle to the escaping of the sperma, 
in case this were injected into the vagina, but I find HaswelTs 
explanation most plausible.) Examining the organisation in Cera- 
toplana colobocentroti, and var. hawaiiensis, one finds that the ductus 
vaginalis has a far more suitable location for the reception of the 
penis than the vagina, The ductus vaginalis forms the direct 
continuation of the antrum femininum, while the vagina opens into 
the antrum femininum at a right angle. The unusual length of 
the ductus vaginalis in C. hawaiiensis, as well as its loop, seems to 
be particularly adapted to prevent the sperma from being ejaculated 
past the median uterine duet and out via the vagina. In this way 
the mass of sperma is effeetively obstructed, and the sperms can 
make their way into the uteri. Still another argument for the use 
of the ductus vaginalis in the copulation act is that the penis, 
lacking a stylet, is very long and unusually narrow. It would 
hardly have such a length if it were only to be inserted into 
the antrum femininum. 
In Bergendalia anomala Laidlaw the ductus vaginalis runs from 
the female orifice strietly upwards, while the vagina is directed 
frontwards. The perpendicular location of the penis in this species 
seems to indicate that the penis is inserted in the ductus vaginalis. 
The diagram of B. diversa, given by Yeri and Kaburaki, does not 
suggest how the act of copulation takes place. Both Laidlaw, and 
Yeri & Kaburaki say that the vagina in the Bergendalia-spQCXQS, 
is „twisted into a remarkable spiral coil, making some five com- 
plete turns** {B. anomala), or „twisted at a part of its course into 
a compact spiral coil of some five turns“ {B. diversa). Unfortu- 
nately, no particulars are given in these descriptions as to the 
openings of the shell giands. Laidlaw merely says: „. . . a great 
number of nuclei massed around the vagina, and probably belong- 
ing to giand cells. Where the vagina turns dorsalwards and be- 
comes spirally twisted it has narrowed slightly, but its epithelium 
retains the characters already mentioned** (— „elongated columnar 
cells the nuclei of which lie near their bases**). Yeri and 
Kaburaki only State that the vagina „is extensively surrounded 
by numerous shell giands**, and their diagram does not clearly 
show the extent of the shell duet. The spiral development of the 
epithelium of the vagina may be intended for the purpose of prolonging 
