124 THE SNAIL. 



along its inner side, between the stomach and the 

 left lobe of the liver. 



4. The common duct arises from the end of the albumen 



gland, close to the point of entrance of the herm- 

 aphrodite duct, and runs forwards through the body 

 almost to the head, lying along the right side of the 

 crop and (Esophagus, and slightly ventral to these. 



It is very wide, and along the greater part of its 

 length is incompletely divided by a longitudinal 

 septum into two parallel ducts. Of these one, the 

 walls of which are thrown into very numerous and 

 prominent transverse folds, serves for the passage of 

 the ova ; while the other, which transmits the sper- 

 matozoa, has a comparatively smooth surface, but 

 has its walls thickened by a whitish glandular pro- 

 static mass. At their anterior ends the two ducts 

 separate completely from each other as oviduct and 

 vas deferens respectively. 

 Slit open the common duct longitudinally ; and note the 

 septum, which partially divides it into male and female ducts. 



5. The male duct and its accessory organs. 



a. The -vas deferens is a slender slightly convoluted 



tube of uniform diameter, which runs forwards 

 along the inner side of the female organs, between 

 these and the buccal mass, passes under the 

 retractor muscle of the right upper tentacle, and 

 then runs back to open into the base of the penis. 



b. The flagellum is along tubular diverticulum, which 



arises from the vas deferens just before it reaches 

 the penis. It lies along the dorsal surface of the 

 crop and other viscera. In it the spermatozoa 

 are agglutinated together to form a long rod-like 

 body, the spermatophore. 



c. The penis is a muscular tube continuous with the 



vas deferens, and lying somewhat obliquely across 

 the oesophagus just behind the buccal mass ; it 



