BTJCCINUM. 319 



The Pedal Ganglia are the largest ganglia in the 

 whelk and are situated most anteriorly. They are oval 

 in shape and lie upon the floor of the perivisceral cavity, 

 in close contact. Consequently there is no pedal com- 

 missure (fig. 42, ped. g.). In the female these ganglia are 

 symmetrical, but owing to the origin of the large penis 

 nerve from the right ganglion, in the male, they become 

 asymmetrical (fig. 43). The pedal ganglia are connected 

 to the cerebral and pleural ganglia on each side by two 

 very short connectives (fig. 42, c.p., pi. p.), a small space, 

 the " triangle lateral," being left between the ganglia 

 and their connectives (fig. 42, tri. lat.). 



A large number of nerves arise from the anterior 

 end of each pedal ganglion and run forwards together for 

 a short distance to plunge into the muscular foot. These 

 are the pedal nerves (figs. 41, 42, fed. n.) and they 

 innervate the entire foot. Other smaller nerves leave the 

 pedal ganglia on both the dorsal and ventral surfaces. 

 According to Bouvier there are two such dorsal (fig. 42, 

 do.) and three ventral nerves (fig. 42, ve.) from each 

 ganglion. The former pass to the head region whilst the 

 latter innervate both the foot in the immediate vicinity, 

 and the floor of the anterior body cavity. 



The penis nerves leave the right pedal ganglion at the 

 posterior lateral corner (fig. 43, P.) and consist of two 

 trunks, one of which is extremely large and follows the 

 \;is deferens inside the penis to form a network from 

 wln'ch delicate branches innervate the muscles of the 

 organ. 



The Cerebral Ganglia will be seen somewhat out of 

 their normal position if the dissection is conducted as 

 described above, for after the severing of the commissure 

 and the removal of the alimentary canal, they will be 

 turned back as indicated in fig. 42, c. 



