378 MOLLUSCA. 



is a racemose body placed at the dorsal summit of the visceral 

 mass in the liver. In the Aspidobranchs as already mentioned it 

 opens into the right kidney, and there is no penis. In the Neri- 

 tidae and Pectinibranchs it has its own duct, which passes along 

 the right side of the rectum (Figs. 280 and 297 e) and opens into 

 the mantle-cavity not far from the anus. 



The penis, which is very generally present, is a muscular, non- 

 invaginable process of the neck of the animal (Fig. 280) on the 

 right side ; and there is a ciliated groove, for the conduct of the 

 sperm, leading from the male opening in the mantle-cavity to the 

 penis, and along the penis to its end (Amputtaria, Littorinidae, 

 Naticidae, Cypraeidae, Heteropoda, Murex, Dolium, Stromlus). 

 In many forms, however, this groove is closed into a canal so 

 that the vas deferens is continued as a tube to the end of the 

 penis (Fig. 280). 



There are not usually accessory glands in the dioecious Gastro- 

 pods, but in some forms there is a glandular region in the oviduct, 

 which secretes albumen, and there is a receptaculum seminis in 

 Neritidae, Paludinidae, Heteropoda, etc. 



In the hermaphrodite Streptoneura there may be an herma- 

 phrodite duct leading to the external opening, or dividing into 

 male and female portions, which open separately ; and the accessory 

 glands are more developed than in the dioecious forms. 



In the Euthyneura the organs are more complicated. The 

 generative gland, which has the same relations as in the Strepto- 

 neura, may be itself hermaphrodite to its ultimate follicles ; or the 

 male and female follicles may be separate, several female follicles 

 being grouped round and opening into a central male follicle 

 (Pleurobranchs, most Nudibranchs). In the streptoneurous form 

 Entoconcha alone are the male and female parts quite separate. 



There is always a single hermaphrodite duct leaving the ovo-testis. 

 In the simplest cases it is undivided (monaulic) and passes to its 

 opening on the right side ; from the latter passes a seminal groove 

 along the side of the body to the penis, which is placed in front 

 (Bullids, Aplysids). In Valvata, Pleurobranchidae, most Nudi- 

 branchs and Pulmonates the duct is diaulic, i.e., at a certain point 

 in its course it divides into the male part the vas deferens, 

 which passes to the penis, and into a female part the oviduct, 

 which passes to the female opening. In the diaulic arrangement 

 the male and female openings are either remote from each other 

 ( Valvata, most Basommatophora, Onchidium, Vaginulus), or close 



