L'98 



Mollusca. 



In the Gastropods there is usually one saccular kidney, 

 opening into the pericardium, and also to the exterior ; if a mantle- 

 cavity is present, the kidney opens into it, otherwise on the right 

 side of the animal. It is usually much folded on its inner surface, 

 and is sometimes much branched. Occasionally there are two 

 kidneys. 



Fig. 244. Male Peri- 

 winkle (Littorima) re- 

 moved from the shell and 

 viewed from above ; mantle 

 cut along the right side 

 and turned over to the left. 

 a anus, d mucous gland, 

 / foot, g oaphradium, h 

 heart, Te gill, I liver, m edge 

 of the mantle,, n kidney, 

 n' urinary aperture, p 

 penis, r seminal groove, 

 s seminal duct, t testis. — 

 After Souleyet, modified. 



The generative organs (Pig. 246) differ very considerably 

 in the different groups ; they have, however, this in common, that the 

 genital aperture is almost always on the right side, and usually within 

 the mantle-chamber when this is present. The Prosobranchiata, 

 which are almost invariably of separate sexes, display the 

 simplest arrangement. In these the ovary and testis, one of each 

 alone being present, are exactly alike externally. The oviduct is a 

 convoluted tube, widened in one region, and opening into the mantle- 

 cavity. The seminal duct in most opens in the same position as the 

 oviduct, and from the genital aperture a groove runs along the 

 surface of the body to the penis, which is situated on the right 

 side of the head ; the groove runs down the copulatory organ to 

 its apex. In others this seminal groove has become a closed canal. 



