The anatomy of Lottia gigantea Gray. 51 



Innervation of the viscera. The nerve supply of the 

 viscera — pharynx, oesophagus, intestine, glands, circulatory system, 

 nephridia and gonad — is derived from the following ganglia: the 

 stomatogastric (buccal), the pleural and visceral (sub-anal, or ab- 

 dominal). The nerves will be taken up in this order. 



Stomatogastric system (buccal or sympathetic, 

 Figs. 33, 35, 39, 42, 43). The two stomatogastric ganglia {Stg. G) 

 and the commissure uniting them are situated on top of the buccal 

 mass in the angle between the pharynx and radula tube, or at that 

 point where the pharynx seems to leave the buccal mass. The ganglia 

 are placed obliquely, each nearing the other posteriorly, where they 

 are joined by a transverse commissure. From the forward end of 

 each ganglion the stomatogastric commissure passes outward around 

 the buccal mass, then downward imbedded in muscle, to join the labial 

 ganglion of that side. On the way, a long nerve is given off into the 

 muscles as already described. From the posterior end of each ganglion 

 a nerve passes outward into the muscles of the buccal mass, and here 

 branches. Another fine nerve starts from the same place and passes 

 into a cord-like muscle on the top of the radula tube, which it follows 

 backward. 



From the posterior end of each ganglion (Fig. 43) a slender 

 nerve passes forward on each side, into what might be termed the 

 upper lip of the radula tube, which serves undoubtedly as a valve to 

 close the mouth of the radula tube. These nerves diverge slightly 

 and on, reaching the front of the lip they branch. A cross nerve 

 passing through the thick tissue of the flap, unites at this point the 

 nerves of the two sides. One branch passes inward and backward 

 along the side of the radula tube; another goes forward and outward 

 around the buccal cartilages; two others pass forward and downward 

 into the buccal mass, and a fifth inward to the front of the lip. 



At about the middle of each stomatogastric ganglion, a small 



nerve {ipn) is given off to the ventral wall of the pharynx. At this 



point the sacculate pharynx narrows, and the ventral wall which is 



thin, turns downward over what has been called the upper lip of the 



radula tube. These smaller nerves (one on each side) pass at first 



forward, then upward and backward under the lesser or ventral folds 



of the pharynx. The nerves anastomose with each other and also 



give off very fine branches which cannot be followed. The two main 



nerves follow the course of the folds, spirally around the oesophagus, 



and enter the proventriculus, along with numerous others, and are 



4* 



