268 MOLLUSC A, 



mass to the stomach— y^\\\c^ is a dilatation of thealimenta 

 tube— and is continued onwards as the intestine, A .xctiu 

 way up the coil the intestine bends on itself and receives the 

 ducts of a four-lobed digestive gland. The fourth lobe 

 occupies the top spiral of the shell. After another bend the 

 intestine ends in the rectum. 



The nervous system consists of ganglia and connectives, 

 but the ganglia are to a large extent concentrated. The 



Nervous ^^^^^^ ^^^ cerebral ganglia) lies dorsal to the 



oesophagus* and is joined by two connectives 



on each side to the ventral nerve-mass. This is formed 



of three pairs of partially-fused ganglia, the pedal, pleural 



and visceral. The brain supplies the eyes and otocysts and 



Sensory ^^ buccal mass, whilst the ventral nerve-mass 

 sends long nerves to all parts of the body. 

 In the substance of the ventral nerve-mass is a pair of 

 otocysts, supplied, as stated, by nerves from the brain. 



The snail is hermaphrodite and the reproductive organs 

 are complex. The genital organ or ovotestis is a small white 

 Reproductive branching organ situated in the spiral lobe of 

 ' the digestive gland. From it the genital duct 

 passes as a coiled white tube down beside the columella. 

 Here it swells into a wide ^mmon duct, and receives the 

 opening of the large albumen gla?id. The common duct has 

 its internal lumen gradually divided into male ( i ) and female 

 ( 9 ) parts by a septum. Eventually these two diverge as the 

 thin vas deferens and the thicker oviduct. The vas deferens, 

 after bending on its course, terminates in a large protrusible 

 penis. At the base of the penis there is a retractor muscle 

 running across to the left side of the body and a long hollow 

 tube or flagellum. The oviduct receives the spermathecal 

 hict, running backwards beside the common duct to ter- 

 minate in the round spermatheca near the upper end of the 

 latter, t" The oviduct leads 'mX,o\h& vagina. Two branched 

 mucus glands then open into this, and it ends at the genital 

 pore beside the male opening. Just at the opening lies a 

 large muscular organ, the dart- sac, in the lumen of which 

 there often is found a calcareous dart. 



* Occasionally the buccal mass is withdrawn through the nerve-ring and the 

 brain is* then found lying in front of the former. 



t In Helix aspersa the spermathecal duct has a long flagellum. 



