GASTROPODA. 



33 



connected together by a transverse band, and each of them gives off 

 a commissure to the pedal ganglia (P g), and a second commissure to 

 a pair of visceral ganglia (Pig}- The latter ganglia, which are 

 known as the commissural or pleural ganglia, are also connected with 

 the pedal ganglia (fig. 497). There are thus two nervous com- 

 missures round the oesophagus the direct cerebro-pedal, and the 

 cerebro-pedal by way of the pleural or commissural ganglia. The 

 pleural ganglia may lie directly on the cerebral or pedal ganglia. 



FIG. 510. Nervous system of Haliotis (diagrammatic, after Spengel). Cg, cerebral ganglion ; 

 Pg, pedal ganglion; Pig, pleural ganglion (commissural ganglion); Ag, abdominal 

 ganglion ; O and O', olfactory organs ; Pe, pedal cord ; S and S', lateral nerves ; Br, 

 gills. b, Nervous system of Limnasus (aftei Lacaze-Duthiers). 



The pleural ganglia are part of the third typical group of ganglia, 

 viz., the visceral group. They are connected with each other by a 

 long commissure, the visceral commissure, which oftey* extends into 

 the hinder part of the body, and contains several ganglia in its 

 course ; the latter ganglia, which also constitute part of the visceral 

 group of ganglia, send off nerves to the sexual organs, kidney, heart, 

 gills, olfactory organs, and mantle (fig. 497, Gs b, V g, Gsp; fig. 510 

 a, 0,0', A g; fig. 510 b, A g}. 



The visceral ganglionic system of Gastropods is therefore broken 

 TOL. IT 3 



