VII 



MOLLUSCA— GENITAL ORGANS 



237 



Helix pomatia and PUurohrandiKa Meckclii afford good examples of this 

 arrangement. 



Helix pomatia (Fig. 193). — From the hermaphrodite gland a hermaphrodite 

 duct, in zigzag coils, passes into the long folded uterus. The straight band wliicli 

 passes along the folds of the uterus is that portion of it which belongs to the seminal 

 duct ; the folds belonging to the female ducts. The seminal channel, however, is 

 merely a furrow within the uterus, divided from the cavity of the latter by two 

 projecting folds, the edges of which become superimposed. A longitudinal glandular 

 band, which is regarded as a prostata, accompanies this duct. At the point where 

 the hermaphrodite duct passes into the uterus, the large linguiform albuminous 

 gland opens into it. At the end of the uterus, the male and female ducts become 

 entirely distinct. The thin vas deferens runs in coils to the oopulatory apparatus, 

 which again opens into the genital cloaca. The oopulatory apparatus consists of a 

 protrusible penis ; at the point where the vas deferens enters this organ, the latter 

 carries a long hollow appendage, the flagellum, the glandular epithelium of which 

 perhaps yields the substance of the spermatophoral capsules. At the same point a 

 retractor muscle is attached to the penis. The 

 short oviduct widens before opening into the 

 genital cloaca. The widened portion has the 

 following appendages : (1) a long stalked pear- 

 shaped receptaculum seminis, lying close to the 

 uterus, — the stalk has a lateral bulging, which 

 is sometimes rudimentary ; (2) two tassel-shaped 

 organs, the digitate glands, the milky secretion 

 of which contains calcareous concretions, and 

 no doubt assists in the formation of the outer 

 envelope of the egg ; (3) the dart sac, which 

 lies close to the cloaca, and contains a pointed 

 calcareous rod, the spiculum amoris, which is 

 thrust by each individual into the tissue of the 

 other as an .excitant during copulation. 



The common outer genital aperture lies in 

 the nuchal region behind the right optic 

 tentacle. 



Pleurobranchaea Meckelii (Fig. 194). — The 

 hermaphrodite duct, which rises from the gland, 

 foi-ms a long ampulla or widening, and then 

 divides into a male and a female duct. The 

 vas deferens runs in coils to the penis sheath, 

 which it enters, coiling up in it almost like a 



watch-spring, and then forms the evaginable Fig. 194.— Genital organs of Pleuro- 

 widened end portion which is called the penis, branolisea Meckelii (after MazzarelU). 



1, Conimou genital aperture ; 2, penis 

 sheatli : 3, penis ; 4, retractor muscle of 

 the same ; 5, vas deferens ; 6, nidaniental 

 gland ; 7, albuminous gland ; 8, genital 

 cloaca ; 9, oviduct ; 10, receptaculum 

 seminis ; 11, widening and c^ecal appen- 

 dage of the oviduct ; 12, hermaphrodite 

 duct ; 13, hermaphrodite gland. 



and which can be invaginated by « retractor 



muscle. The oviduct has a shorter course, and 



receives the short efferent duct of a globular 



receptaculum seminis. The widened terminal 



portion of the oviduct (the vagina), which enters 



the genital cloaca with the penis, receives the 



ducts of the albuminous and nidamental glands 



(shell and slime glands) ; the second of these may be regarded as the homologue of 



the digitate gland of Helix. 



There is a general agreement between the ducts of the NudihrancMa and those 

 just described ; in details, however, extraordinary variety prevails. The male and 



