320 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Auriculidae, namely, Auricula myosotis, Draparnaud (see text-figure B). 
The primitive (hermaphrodite) genital opening (O.Y.) is just outside the 
mantle chamber and serves only for the exit of the ova. From this 
pore there is a lateral groove (Ep.Gr.) running forward to the penis; but 
lying in the sub-epidermal tissues, just below the groove, there is a ciliated 
tubular vas deferens (Y.D.) which receives the spermatozoa (at O.Y.D.) as 
they issue from the hermaphrodite duct, and conducts them to the large 
muscular eversible tubular penis (P.). Thus, by conversion of the ciliated 
seminal groove into a closed tube, the hermaphrodite aperture has been 
converted into a functionally female aperture, and the male opening (M.O.) 
has been secondarily moved forwards from its primitive position so that 
male and female pores are some distance apart. 
In the rest of the Pulmonata the hermaphrodite duct divides into male 
and female ducts. In the Basommatophora the female aperture retains a 
position similar to that of the primitive genital opening of Auricula , so 
that the male and female pores are separate.* In the Stylommatophora 
the female pore has undergone secondary forward movement and is closely 
associated with the male pore, the two openings being situated in a common 
genital atrium. j - 
The penis and vas deferens of the abnormal specimen of Helix are 
interesting as* showing, as it were, two different phylogenetic stages — 
namely, the Pythia-st&ge on the left and the normal condition for Helix on 
the right. The supplementary vas deferens and the retracted penis form a 
U-shaped loop, both ends of which are in contact with the epidermis, as in 
Pythia ; in fact, they so closely resemble the corresponding structures 
figured by Plate in Pythia that these organs may be described as having 
identical relations in the two forms, except that in the supplementary 
organs of Helix the vas deferens has no pore at its epidermal end, and that 
it bears a blind outgrowth — the flagellum — which is not present in Pythia. 
While it is impossible to explain the cause of the development of the extra 
organs in this specimen of Helix, it would seem that, assuming that like 
causes produce like effects, whatever cause (in the ontogeny) has brought 
about their formation must have been closely similar to, if not identical 
with, that which has been responsible for the development of the corre- 
* Except in the genus Amphibola and the family Siphonariidae where the male and 
female ducts open into a common genital atrium. 
t Except in the families Oncidiidae and Yaginulidae and the genus Atopos , where a 
separation of the genital pores has been brought about by detorsion, which has caused the 
anus and the female opening to move backwards, so that the latter now lies, in Vaginula 
about the middle of the right side and in Oncidiella and Atopos posteriorly near the anus. 
These are to be regarded as specialised rather than as primitive forms (Pelseneer, 1901, p. 27). 
