74 



THE NERVOUS SYSTEM OF MOLLUSKS. 



harrowing organ ; to many it aids in the execution of 

 short leaps." 



The hivalves possessing a foot, therefore, present three 

 pairs of ganglia instead of two — the anterior or ' lahial', 



Fig. 23 —Nervous Systoin of th ; Conmiou Mussel. (After Owen.) I, Tvabial ganglia 

 connected by a short conini ssu o above or in front of the mouth; b, !>, branchial 

 ganglia similarly connected, and also united by very long cords (</, d) witli the labial 

 ganglia ; 2K bilobed pedal ganglion sending branches to tlie muscular foot (,r), and 

 clo.'iely connected with the 'auditory saccules' (s) ; h, h', circum-pallial plexus; 

 y, byssus. by which the animal attaches itself to external substances. 



the posterior or ' hranchial', and the inferior or * pedal'. 

 It occasionally liai)peiis that the ganglia of the posterior 

 or even of the inferior pair may hecome approximated and 

 fused into one. 



