214 



NERVOUS SYSTEM. 



The vermetus has, like the aptysia, a small anterior infra- 

 oesophageal ganglion besides the ordinary supra-oesophageal 

 and two lateral ganglia ; the infra-oesophageal ganglion is 

 situate beneath the muscular bulb of the oesophagus, and a 

 small sympathetic ganglion, placed near the stomach, receives 

 filaments from the lateral ganglia, and sends nerves to the 

 abdominal viscera. In the long body of the dentalium the 

 brain forms a single lengthened quadrilateral ganglion ex- 

 tended longitudinally above the oesophagus, and sending 

 down small nerves on each side to complete the cesophageal 

 ring. In the pulmonated gasteropods the brain is generally 

 more equally divided between the upper and lower surfaces 

 of the cesophageal ring, the broad ganglia in these two situa- 

 tions having a bilobate form. The highest forms of the pec- 

 tinibranchiate gasteropods, as the buccinum and the harpa, 



FIG. 92. 



