318 Proceedings of the Royal Society of Edinburgh. [Sess. 
smaller, situated in the vagina. The vas deferens was single in its proximal 
part hut bifurcated distally, each of the two portions passing to one of 
the supernumerary penes. The vas deferens of the normal penis was 
represented by a small bud. Each of the penes had a flagellum and a 
retractor muscle. Paravicini (1898) had previously described a somewhat 
similar case in which three penes were present and the vas deferens 
was branched, but only one of the penes was functional. Both these are 
examples of meristic variation, possibly produced by division of the penis 
rudiment at an early period of its development, and they differ essentially 
from the case of the Helix with paired penes. 
Before passing to the consideration of the significance of the abnormality 
in regard to the origin and relations of the genital ducts in Pulmonata, 
it will be of advantage to briefly review the comparative anatomy of the 
genital ducts of a few Gastropods. 
In the Pectinibranchiata (Monotocardia) the genital duct of the female 
opens into the pallial chamber near the anus. In many of the Taenioglossa 
and some of the Rachiglossa and Heteropoda the aperture of the genital 
duct in the male is also situated in the pallial chamber, and in many of the 
less specialised forms of these groups there is, in those males which possess 
a penis, a ciliated seminal groove which extends from the genital pore 
forwards along the right side of the body to the base of the penis, which 
organ is usually non-introversible and is situated on the head or “ neck.” 
The spermatozoa are conducted by this groove from the genital pore to the 
base of the penis, where they are led into a deep groove or tube which 
traverses the penis to its tip. 
A comparable condition is found in many Tectibranchs, in which the 
aperture of the hermaphrodite duct is on the right side, within but near 
the opening of the mantle cavity. From this aperture the fertilised ova 
escape directly to the exterior, but the spermatozoa pass into a ciliated 
groove which runs along the right side of the body and head to the penis, 
which is introversible (except in Actaeon). 
Within the Pulmonata there are forms which exhibit stages of special- 
isation of the genital ducts connecting the condition just described with 
that seen in Helix. The most interesting of these stages in relation 
to the subject of the present paper is that presented by the primitive 
Auriculid, Pythia scarabeus, L ., described by Plate (1897) (see text-figure A). 
In this animal the hermaphrodite- or common-duct opens at the genital 
pore (G.O.) situated just outside the mantle chamber but near the pulmonary 
aperture ; and from this point a ciliated groove (Cil.Gr.) runs forwards on 
the right side of the body to the aperture of the vas deferens. Here the 
