88 



the sense cells. The pallial muscles are also innervated 

 by branches from the circumpallial nerve. The circiim- 

 pallial nerve is connected with both the cerebro-pleural 

 and visceral ganglia ; with the former by the anterior 

 pallial nerves (N. j^a.) already described (figs. 16 and 18, 

 N. pall.). 



The pallial nerves from the visceral ganglion do not 

 pursue a similar course on the right and left sides of the 

 body. On the right, that is, the side on which the gill is 

 attached to the mantle, the pallial nerves pass out as a 

 large trunk very close to the branchial nerve, and run 

 alongside this until the point is reached where the 

 branchial nerve enters the gill lamellae. 



Here they enter the mantle, and at once divide into 

 branches which radiate out to the circumpallial nerve 

 (fig. 3, N. 'palL). The main branch, iiowever, passes 

 along in the mantle, after bending sharply, exactly in the 

 line of attachment of the basal gill lamellae, and from 

 this the various branches arise. 



On the left side the distribution is somewhat different. 

 The pallial nerves are not collected to form a large trunk, 

 but radiate out directly from the ganglion over the siirface 

 of the adductor muscle until the mantle is reached ; 

 entering the mantle, they pass out, branching on the way, 

 to the circumpallial nerve. In all probability these 

 pallial nerves also innervate the pallial muscles. There 

 are, in addition to the pallial nerves already described, 

 certain nerves which leave the visceral ganglia from the 

 posterior angles of the lateral lobes, and pass directly back 

 over the surface of the adductor until they reach and enter 

 the mantle opposite the terminal point of attachment of 

 the rectum (fig. 28, N . pp.). 



With regard to the histology of the visceral ganglion, 

 the ganglion cells are, for the most part, grouped over the 



