XII 



PHYLUM MOLLUSCA 



697 



The nephridia of the Gastropoda are dorsally placed glandular 

 tubes or chambers, which communicate internally with the peri- 

 cardium, and open on the exterior close to the anus, either 

 directly or through a duct the ureter. Both right and left neph- 

 ridia may be present, though unequal in size, the one situated to 



to 



the 

 In a 



rec.sem 



the right of the anus being larger than that situated 



left; or the former may alone be developed (j&uthyneura). 



very limited number 



of Gastropoda the 



gonad opens into the 



nephridium. 



The sexes are separ- 

 ate in nearly all the 

 Streptoneura, united 

 in the Euthyneura. 

 Special gonoducts are 

 present, except in one 

 or two forms in which 

 the nephridia perform 

 that function. In the 

 unisexual forms the 

 reproductive apparatus 

 is of a comparatively 

 simple character, con- 

 sisting merely of a 

 racemose reproductive 

 organ, ovary or testis, 

 as the case may be, 

 situated dorsally in the 

 visceral spiral, with the 

 gonoduct opening far 

 forwards on the right- 

 hand side, and, in the 

 male a penis, which is 

 grooved longitudinally 

 and non-retractile. In 

 the hermaphrodite 

 forms, such as the 

 Pulmonata (Fig. 603), 

 on the other hand, a 

 considerable degree of complexity is observable. There is a 

 hermaphrodite gland (herm. gl., Fig. 604, A\ some of the follicles 

 of which produce ova, while others produce sperms, a convoluted 

 hermaphrodite duct (herm. d.\. an albumen^ gland, in which 

 the albumen of the relatively large eggs is formed, separate 

 oviduct and spermiduct leading to a common genital opening, 

 In addition there is a receptaculum seminis (i'cc. sem.) connected 



r&c.s&m.ap NT^/Z 



FIG. 603. Reproductive organs of Helix, alb. gl. albumen 

 gland ; d. s. dart sac ; flag, flagellum of the penis ; 

 herm. <il. hermaphrodite gland ; kcrm. d. hermaphrodite 

 duct ; nmc. gl. mucous gland ; muc. gl. ap. apertures of 

 mucous glands into vestibule ; ovid. oviducal part of the 

 common duct ; orid. ap. aperture of oviduct into vesti- 

 bule ; pen. penis ; rtc. sem. receptaculum seminis ; rcc. 

 sem. ap. aperture of receptaculum seminis ; sp. d. sperm 

 duct ; sp. d'. spermiducal part of common duct. (-After 

 Pelseneer.) 



