71 



the body cavity. The branches of this nerve are quite 

 easily seen if the nerve collar in situ is pressed slightly 

 over to the left side. The branches pass out directly to 

 the right. 



The Supra- and Sub-intestinal Ganglia. Three 

 prominent nerves are easily seen crossing the floor of the 

 anterior cavity and entering the wall on the right side. 

 The most anterior of these is more delicate than the other 

 two. All arise in the sub-intestinal ganglion (fig. 42, 

 sub. int.). The two larger are the pallial nerves (figs. 

 41 and 42, pall, n.), and after plunging through the walls 

 of the body cavity they reach and divide up on the 

 mantle, the more anterior of the two forming an 

 extensive network. 



The branches of these pallial nerves of the right side 

 come into contact with the branches of the left pallial 

 nerves. This takes place in the mantle immediately 

 above the pallial cavity. Thus a continuous network is 

 formed running around the mantle edge. 



A number of other small nerves (fig. 42) arise in the 

 sub-intestinal ganglion and innervate the walls of the 

 body cavity and the columellar muscle. 



The largest nerve leaving the sub-intestinal ganglion 

 arises from the left posterior corner. It is the Visceral 

 Commissure itself (figs. 41 and 42, Vis. com.). This 

 cord runs posteriorly almost in the middle line, in close 

 contact with the floor of the body cavity, for some 

 distance, and then passes underneath the most superficial 

 muscle fibres. It is often very difficult to dissect out the 

 visceral loop in the whelk, but if the specimens have been 

 preserved in spirit, the track of the visceral commissure 

 is visible as a delicate ridge on the floor of the body 

 cavity running back from the point x in the figure. 



The visceral ganglia are situated on the loop just 



