THE GASTROPODA 127 
when the female duct becomes bifurcated through the separation 
of the bursa copulatrix, the latter acquiring a separate external 
aperture but remaining in connection with the oviduct by its 
deeper extremity. In this manner two female orifices are 
formed; the one is the copulatory orifice, the other is the 
oviducal orifice serving for the passage of the ova. The genital 
duct is thus trifurcated or “ tri- 
aulic,” a condition which is not 
found in any Pulmonate, but is 
confined to certain Nudibranchs, 
viz. the Doridomorpha and the 
majority of the Elysiomorpha 
(Fig. 105). 
Fic. 104. 
Hermaphrodite reproductive appara- 
tus of Helix hortensis. d, digitate acces- 
sory glands on the female duct; E.d, 
dd 
Fic. 103. albuminiparous gland; jl, flagellum; p, 
penis; p.s, calciferous gland or dart-sae 
Oncidiopsis, hermaphrodite genital on the female duct; Z.s, receptaculum 
apparatus, dorsal view. a.g, albumini- seminis or spermatheca, opening into the 
parous gland; /.0, female orifice; g.g, female duct; uw, uterine dilatation of the 
hermaphrodite gonad; pe, penis; pr, hermaphroditic duct; v.d, spermiduct or 
prostate; 7.s, receptaculum  seminis ; vas deferens ; v.e, hermaphroditie duct ; 
so, spermoviduct; sp, spermiduct; s.v, 2, ovo-testis. (From Ray Lankester, 
seminal vesicle. after Gegenbaur.) 
The penis is invaginable in all the Euthyneura with the 
exception of Actacon (Fig. 148, VI) and Umbrella. It is a pedal 
structure in nearly all Opisthobranchia, but in Umbrella it is 
cephalic. In the majority of Pulmonates the penial nerve arises 
from the cerebral ganglion, but the fibres of the nerve originate 
from the pedal and only traverse the cerebral ganglion. In 
monaulic species the penis often bears an appendage, and 
occasionally chitinous accessory structures: there is a_ single 
stylet in several species of Planorbis, in Glaucus, and many other 
