MOLLUSGA— GENITAL ORGANS 



237 



afford good examples of this 



HelLc pomatia and Plcm'ohranchci:a Mcckeli 

 arrangement. 



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

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

 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, tlie 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 copulatory apparatus, 

 which again opens into the genital cloaca. The copulatory 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 

 I'etractor 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 

 iiterus, — 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. 



Pleurobranchsea Meckelii (Fig. 194).— The 

 hermaphrodite duct, which rises from the gland, 

 forms 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 



widened end portion which is called the penis, branchaea Meckelii (ufter Mazzarelli). 

 and which can be invaginated by a retractor l, Coiuiikhi gi'iiital apprtuie ; i, penis 

 muscle. The oviduct has a shorter course, and sheath ; 3, penis ; 4, retractor muscle of 

 ,1 1 J. a' i. 1 i f 111 the same ; 5, vas deferens ; 6, nidaniental 



I'eceives the short efterent duct of a globular , , - , • , , » 



° gland ; i , albuminous s'and ; S, genital 



receptaculum seminis. The widened terminal cloaca; 9, oviduct; 10, receptaculum 

 portion of the oviduct (the vagina), which enters seminis ; 11, widening and csecal appen- 

 the genital cloaca with the penis, receives the '•^S*' °^ t^e oviduct ; 12, liermaplirodite 

 ducts of the albuminous and nidamental glands ^"'='^= ^^' '^rm^P'-rodite gland, 

 (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 Nudibranchia and those 

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



Fic;. 194.— Genital organs of Pleuro- 



