144 HERMAPHRODITE MOLLUSCA, GENERATIVE ORGANS chap. 



the whole circumstances of the occurrence, position, and pres- 

 ent use of the darts. 



Hermaphrodite Mollusca. — (5) Bigonopora. — As an exam- 

 ple of the Digonopora or hermaphrodite Mollusca with separate 

 generative apertures for the male and female organs, we may 

 take the common Limnaea stagnalis (Fig. ^b). It will be seen 

 from the figure that the relative positions of the hermaphrodite 

 gland and duct, and of the albumen gland, are the same as in 

 Helix. When the oviduct parts company from the vas deferens, 

 it becomes furnished with several accessory glands, one of which 

 (gi.e.) probably serves as a reservoir for the ova, and answers 

 more or less to a uterus. The tube leading to the spermatheca 



Fig. 55. — Genitalia of Limnaea stagnalis 

 L. (from a dissection by F. B. Stead), 

 x2. 



A.G, albumen gland. 



Ac.G, accessory' gland. 



F.O, female orifice. 



GI.E, glandular enlargement. 



H.D, hermaphrodite duct. 



H.G, hermaphrodite gland. 



Li, liver. 



M.O, male orifice. 



P, penis sac. 



Pr, prostate. 



R.M, retractor muscle of penis. 



Sp, spermatheca. 



V.D, vas deferens. 



is short, and there is no divergent coecum. The female orifice 

 lies near to the external opening of the branchial cavity. The 

 vas deferens, which is very long, is furnished with a large pros- 

 tate gland. The penis sac is greatly dilated, and there is no 

 flagellum. The male orifice is behind the right tentacle, 

 slightly in advance of the female orifice (compare Fig. 102). 



Most of the Opisthobranchiata, but not all, have separate 

 sexual orifices. Numerous variations from the type just de- 



