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 pleura! 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. 



Br- 



FIG. 510. Nervous system of ffaliotis (diagrammatic, after Spensel). C/, cerebral ganglion ; 

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

 ganglion ; O and O', olfactory organs ; PC, pedal cord ; S and -$', lateral nerves ; Br, 

 gills, b, Nervous system of Limnceits (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 often 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, G s b, V g, G sp; fig. 510 

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



The visceral ganglionic system of Gastropods is therefore broken 

 VOL. ii. 3 



