317 
1906-7.] Helix pomatia with Paired Male Organs. 
from the external aperture, and probably this last portion of the tube ought 
therefore to be regarded as atrium. This view is supported by the character 
of the external opening, which agrees in every respect with that of the pore 
of the normal genital atrium. This left atrium, the inner surface of which 
is traversed by shallow transverse folds, is rather shorter than the right 
(normal) atrium, and its walls are slightly thinner. 
There is no trace of connection between these supernumerary organs and 
the ovotestis or the genital ducts of the right side. 
The duplication of genital organs in this specimen of Helix presents 
features of interest from three aspects, (1) on account of its rarity, (2) 
because the form of the supernumerary organs has a significance in relation 
to the phylogeny of the genital ducts in Helix, and (3) in regard to certain 
points in the ontogeny of the male organs of Helix. 
This abnormality is not in the same category as those moderately 
numerous instances in which organs, normally situated in the middle line, 
have been found in a state of more or less complete division — for example, 
the penis of mammals. The penis of Helix is never median, and there is no 
trace of any connection between the two penes of this abnormal specimen 
to suggest that they have been produced by division of a single penis 
rudiment. In the duplication of the penis and its associated structures this 
snail presents an example of lateral homoeosis which is extremely rare in 
the Mollusca ; in fact the only case,* known to me, at all comparable to this 
one is Appellof’s (1893, p. 14) record of a specimen of Eledone cirrhosa 
( — Moschites cirrosa), in which not only was the third right arm hecto- 
cotylised, as usual, but the third left one also. There were on the right 
arm 57 suckers and on the left 66 ; both arms presented the normal plan of 
hectocotylisation and were practically equally developed. There was no 
corresponding duplication of the internal sexual organs. This specimen 
therefore presents interesting parallels to the abnormal Helix in that (1) 
the duplicated sperm-transferring organ and the normal one are sym- 
metrically placed with regard to the median plane and are practically 
equally developed, and (2) there is no modification of the normal sexual 
organs. 
Repetition of the penis on the right side has been twice recorded in 
Helix pomatia, but reference to these cases shows that they are essentially 
different to the one under consideration. Pegot (1900) described a specimen 
with three penes, one in its usual position and communicating with the 
genital atrium by a large canal, the two others, similar in structure but 
* A Pteropod with paired penes has recently been described by Meisenheimer ; see 
Addendum, p. 327. 
