1903.] POLYCLADS OF THE ‘‘ SKEAT EXPEDITION.” 311 
consists of a very thin layer of circular muscle-fibres, lined with 
a cubical epithelium, the nuclei of the cells of which lie close to 
the lumen, and which has rather the appearance of an exhausted 
secretory tissue. This organ I call the prostate (Pl. XXITT. fig. 4, 
pro.). About halfway between the penis and female aperture lies 
an organ which bears some resemblance to the penis already 
described. This organ constitutes one of the most interesting 
features of this anomalous species. It consists of a small pro- 
trusible penis-like organ (p.?), about one-third the size of that 
first described, lying ina small antrum. It is pierced by a short 
duct, which runs into it from a small non-muscular vesicle which 
lies immediately above it (p7.?). This small vesicle is of about 
- the same size as the prostate. There is no communication, so far 
as I can discover, between the duct connecting these structures 
and the vasa deferentia (Pl. XXITT. fig. 5). 
Text-fig. 54, 
Genital apparatus of Bergendalia anomala. 
ace., accessory part of vagina; p. ?, penis-like organ; pr. ?, prostate-like organ ; 
s., spiral coils of vagina. For other letters, see p. 318. 
I can suggest only two explanations of the presence of this 
second penis-like organ and its accessories. 
Firstly, that it may be regarded as a prostatic structure which 
has lost its connection with the penis and developed an intro- 
mittent terminal part of itsown. Such a state of affairs is found 
in the Cotylean family Diposthiide ; but in that case both penis 
and prostate open into a common antrum, and there is what 
appears to be a prostate gland in connection with the penis in 
Bergendalia, a fact which makes strongly against this view. 
The second possible explanation is that the organs under dis- 
cussion are the vestiges of asecond penis. The fact that they bear 
a close resemblance to the functional penis tends to support this 
view, as does also, I think, a comparison with Cryptocelides of 
Bergendal [1]. 
This is the only other Polyclad described, so far as I know, in 
which two penial organs lie behind each other on the middle line ; 
but, according to Bergendal, they lie behind the female aperture, 
and, further, both open intoa common antrum, whilst in some cases 
