68 Invertebrate Zoology. 



considerable bilateral asymmetry. If the anterior part of 

 the oesophagus is turned back, however, the lower side of 

 the ganglionic mass will be found to be made up of two 

 nearly equal halves. 



Lying ventrally are the small buccal ganglia, a pair of 

 spherical bodies somewhat in front of the remaining ganglia 

 and giving origin to a number of nerve-strands that pass to 

 the pharyngeal apparatus. A buccal commissure runs beneath 

 the oesophagus and connects the right with the left ganglion. 



Also, on the ventral side of the oesophagus are the much 

 larger pedal ganglia. These lie, fused together, a little pos- 

 terior to the buccal ganglia, and from them large strands of 

 nerves pass to the right and left halves of the foot. 



Cerebro-pedal connectives pass from the pedal ganglia 

 dorsally, partially encircling the oesophagus, and uniting with 

 the cerebral ganglia. The cerebral ganglia rest dorso-later- 

 ally upon the oesophagus, and are united dorsally by the 

 cerebral commissure. Nerves pass from the cerebral ganglia 

 to the region of the head. Cerebro-buccal connectives unite 

 the buccal and cerebral ganglia. 



The left cerebral ganglion is in union ventrally and pos- 

 teriorly with the left pleura! gang/ion, which rests anteriorly 

 upon the posterior part of the left pedal ganglion. 



The right cerebral ganglion at first appears to be some- 

 what larger than its fellow. Examination will show that this 

 is because of its partial fusion with the right plural ganglion, 

 which lies immediately ventral and posterior to it. 



At the posterior edge of the right pleural ganglion, the 

 pear-shaped right visceral or supra-intestinal ganglion is 

 seen to be attached. It lies almost directly upon the dorsal 

 surface of the oesophagus, and gives off several branches, of 

 which two go to the osphradium, and a third passes pos- 



