IV.] THE COMMON SNAIL. 297 



to the supra-oesophageal of its own side by a 



cerebro-pedal commissure. 



d. The parieto-splanchnic ganglia; a series of gangli- 

 onic masses lying in close apposition, immediately 

 behind and a little above c. They give off fibres 

 (on the right side three sets and on the left two), 

 which enter the body wall at the base of the 

 visceral sac. 



The anterior fibres (pallial nerves] enter the 

 thickened border of the lung sac, within which they 

 anastomose. 



The ganglia of either side are connected with 

 the supra-oesophageal by a cerebro-splanchnic com- 

 missure^ which runs parallel with but is somewhat 

 shorter than the cerebro-pedal one. 



e. The posterior-visceral nerve; a single nerve arising 

 from d. altogether to the left side. It passes back 

 immediately beneath the anterior aorta (which it 

 accompanies) to enter the visceral sac. On doing 

 so, it gives off branches as under 



a. A main one, running on to reach the left side of 

 the visceral sac. 



/3. A right one, whose fibres can be traced to the 

 albumen-gland and duct of the ovotestis. 



y. A dorsal one, arising from the main trunk, in 

 the immediate vicinity of the enlarged head of 

 the spermatheca. It is distributed to the excre- 

 tory-organ and heart. 



2. Remove sufficient of the cephalic wall of the right 

 side to expose the whole buccal mass. Look for 



