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). 



FIG. 103. 



Oncidiopnia, hermaphrodite genital 

 apparatus, dorsal view, a.g, albumini- 

 parous gland; /.o, female orifice; g.g, 

 hermaphrodite gouad ; pe. penis : nr, 

 prostate ; r.s, receptaculum seminis ; 

 so, spermoviduct ; sp, spermiduct ; s.v, 

 seminal vesicle. 



FIG. 104. 



Hermaphrodite reproductive appara- 

 tus of Helix, hortensia. d, digitate acces- 

 sory glands ou the female duct ; E.d, 

 albuniiuiparous gland ; fi, flagellmu ; ji, 

 penis; p.s, calciferous gland or dart-sac 

 on the female duct ; It.g, receptaculnm 

 seminis or spermatheca, opening into the 

 female duct ; u, uterine dilatation of the 

 hermaphroditic duct ; v M, spermiduct or 

 vas deferens ; v.e, hermaphroditic duct ; 

 z, ovo-testis. (From Kay Lankester, 

 after Gegenbaur.) 



The penis is invaginable in all the Euthyneura with the 

 exception of Adaeon (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 



