Pelecypoda. 117 



Nervous System of the Clam. There are three pairs 

 of ganglions, which are connected by nerve trunks, called 

 commissures : 



1. The cerebral ganglions, one on each side of the 

 mouth, just above the outer palp of each side; these are 

 connected by a nerve cord which passes over the gullet. 



2. The two pedal ganglions, lying closely side by side, 

 deeply imbedded in muscle, near the middle of the foot. 

 Each of these is connected with the cerebro-pleural gan- 

 glion of its side. 



' Gullet 



Visceral 

 Ganglions 



FIG. 72. CLAM, NERVOUS SYSTEM. 



3. On the under surface of the posterior adductor are 

 the two visceral ganglions, apparently forming one double 

 ganglion. These ganglions are much easier to find than 

 the others. Each of these is connected with the cerebral 

 ganglion of its side by a nerve cord, which runs along in 

 the dorsal part of the body for a good share of its length. 

 From all of these ganglions nerves extend to supply the 

 adjacent regions. 



