136 GENERATIVE ORGANS OF DIOECIOUS MOLLUSCA chap. 



capsule, as the case may be) in which the fertilised ova become 

 enclosed previous to exclusion. In position the oviduct abuts 

 on the kidney, while the uterus is in close proximity to the 

 rectum, and the female external orifice is found close to the 

 anus, within the branchial cavity. 



The male organs of Llttorina are more simple. The testis is 

 lodged, like the ovary, in the liver; the vas deferens is, like the 

 oviduct, convoluted, and eventually traverses the right side of 

 the neck, emerging near the right tentacle, and terminating in 

 the penis or external copulative organ (Fig. 50). 



This system prevails, with but slight modifications in detail, 

 throughout the prosobranchiate Gasteropoda. The most impor- 

 tant modification is the passage of the seminal products in certain 

 cases (many of the Diotocardia) through the right kidney, with 

 which the oviduct and vas deferens always stand in close rela- 

 tion. The same arrangement occurs in the Scaphoda and some 

 Pelecypoda. 



The penis varies greatly in form and size. In the Strombidae 

 (see Fig. 99) and Buccinidae (Fig. 62) it is very large and 

 prominent ; in Littorina it is somewhat spinulose at one side ; 

 in Paludina a portion of it is lodged in the right tentacle, which 

 becomes atrophied and much more obtuse than the tentacle on 

 the left side. 



Spermatozoa. — The shape of the spermatozoa and of the 

 ova in Mollusca is of the usual type. In Paludina Ampullaria, 

 and certain species of Murex two types of spermatozoa occur, 

 one hair-like, the other worm-like, three times as long as the 

 former, and not tapering at one end. The former type alone 

 take part in fertilisation, and penetrate the ovum. It has been 

 suggested that these worm-like spermatozoa are a kind of incipi- 

 ent ova, and indicate a possible stage in commencing hermaphro- 

 ditism. And, since the nearest allies of the Prosobranchiata 

 (in which these types occur) are hermaphrodite (i.e. the Opis- 

 thobranchiata and Pulmonata), it is not unreasonable to suppose 

 that the Prosobranchiata should show some tendency towards 

 hermaphroditism in their genital glands.^ 



Cephalopoda. — The special characteristic of the reproduc- 

 tive organs in female Cephalopoda is the development of various 

 glands, some of considerable size, in connexion with the ovary 

 and oviduct. Sepia, Loligo, and Sepiola are furnished with two 



1 Von Brunn, Arch. Mikr. Anat. xxiii. p. 413. 



