136 GENERATIVE ORGANS OF DIOECIOUS MOLLUSCA chap. 



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 Littorina 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 important 

 modification is the passage of the seminal products in certain cases 

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

 the oviduct andvas deferens always stand in close relation. The 

 same arrangement occurs in the Scaphopoda 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 promi- 

 nent ; 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 MoUusca is of the usual type. In Paludina, Ampullaria, 

 and certain species of Murex two types of spermatozoa occm% 

 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 

 incipient ova, and indicate a possible stage in commencing 

 hermaphroditism. And, since the nearest allies of the Proso- 

 branchiata (in which these types occur) are hermaphrodite {i.e. 

 the Opisthobranchiata 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 reproductive 

 organs in female Cephalopoda is the development of various glands, 

 some of considerable size, in connexion with the ovary and 

 oviduct. Sepia, Loligo, and Sejpiola are furnished with tw^o large 

 nidamental glands, which open into the mantle cavity independ- 



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



