IV.] THE COMMON SNAIL. 2QI 



<?. The oviduct; a very short thick-walled tube, entering 

 into immediate relationship with a large white sac 

 the dart sac ( 3 e). 



f. The 7'as duferens ; a thin-walled tube, arising side by 

 side with g, but of lesser calibre than it. Its inner 

 end is tied down to the female duct ; leaving this 

 it passes under the retractor muscle of the right 

 tentacles and becomes enlarged to form 



g. the penis, apparent now as the ' elongated swollen 

 end of the vas defer ens. It passes to the exterior 

 side by side with the female duct. 



It is attached to the body-wall of the left side by 

 a ribbon-shaped retractor muscle. Cut this across 

 and displace the whole organ. 



h. The spermatophoral gland (xflagellum; an elongated 

 thread-like diverticulum of the base of the penis. 

 It is much coiled. 



3. Remove the entire reproductive system from the body, 

 together with a portion of the body-wall immediately 

 adjacent to the sexual orifice. Pin the whole down 

 carefully under water, and open up the larger ducts 

 and their appendages, as they stand related to the 

 exterior. Make out in order : 



a. The genital cloaca or vestibule ; a shallow integu- 

 mental pit, opening on to the exterior by the single 

 genital orifice. 



b. The penis. Remove a portion of its enlarged 

 eversible base. It opens into the front wall of the 

 vestibule ; its lining membrane is produced into a 

 fold or prepuce, above which there is usually an 

 eminence. 



19 2 



