69 



are very easily overlooked, even when one examines the 

 exact place where they occur. They are about two milli- 

 metres apart and 0"5 mm. in diameter. 



In addition to these sensory nerves, there are two 

 other groups which have their origin in the cerebral 

 ganglia, i.e., the nerves of the proboscis and of the 

 cephalic integument. The former arise just anterior to 

 the cerebral commissure and form a compact bundle on 

 each side, ascending with the salivary ducts and running 

 along with them towards the proboscis. They innervate 

 that organ and also the proboscis sheath. The cerebral 

 nerves of the proboscis enter into close relation (forming 

 anastomoses) with certain nerves from the small buccal 



Fig. 6. 



ganglia, and all pass together into the proboscis. The 

 buccal nerves innervate the oesophagus and radular 

 apparatus, the cerebral nerves on the other hand appear 

 entirely concerned with the walls of the proboscis itself. 

 There are two other nerves innervating the integument of 

 the head region and these arise from the cerebro-pedal 

 connectives (Text-fig. 6, ceph. n.). They eventually 

 branch, sending numerous twigs to the region immediately 

 posterior to the tentacles. 



The Pleural Ganglia are asymmetrical owing to the 

 positions taken by the supra- and sub-intestinal ganglia 



