A LAND SNAIL 121 



oviduct ; the mucous glands, two bunches of tubular glands ; and 

 the dart-sac, a thick-walled sac which contains a calcareous spicule. 

 Identify these organs. 



The vas deferens, after separating from the oviduct, passes 

 under the retractor muscles of the tentacle to the distal end of 

 the penis. This organ has already been noted ; it is tubular in 

 shape and lies in a bent position across the oesophagus. A 

 retractor muscle inserted at the bend connects it with the dorsal 

 body-wall. At the point where the vas deferens meets it is the 

 flagellum, a long, tubular sac into which spermatozoa pass from 

 the vas deferens and where they are massed together to form 

 spermatophores. Both penis and vagina communicate, side by 

 side, with the genital cloaca, which opens to the exterior through 

 the common genital pore. 



When two animals pair each receives a spermatophore from 

 the other. This passes into the receptaculum seminis, which 

 is thus filled with the spermatozoa of the other animal, and 

 these finally fertilize the eggs as they pass into the vagina from 

 the oviduct. 



Exercise 7. Make a semidiagrammatic drawing of the reproduc- 

 tive organs on a scale of 2. 



Split the dart-sac and take out the dart ; mount it on a 

 slide in water or glycerine and examine it under a compound 

 microscope. 



Exercise 8. Draw the dart. 



The nervous system. Sever the oesophagus and remove the 

 reproductive and digestive systems, leaving the pharynx in 

 the body and taking care not to injure any of the nerves. The 

 principal ganglia are contained in the nerve collar. The two 

 supracesophageal ganglia, which constitute the brain, will be seen 

 joined by a broad transverse commissure. From their anterior 

 surface nerves run to the tentacles, and from their inner 



