156 



fusion of the two ventral and dorsal roots, as described 

 above. It passes up the anterior wall of the cardiac fore- 

 gut as a median nerve. About half way along this wall 

 the nerve enlarges to form the stomato gastric ganglion 

 (st. g.). From this point the nerve proceeds backward 

 along the dorsal side of the fore-gut, and almost 

 immediately gives off two large branches — the lateral 

 gastric nerves (7. g. n.). Each lateral gastric nerve passes 

 over the anterior cardiac muscle, which it innervates, and 

 gives rise to a nerve plexus in the dorsal walls of the 

 cardiac fore-gut. Both nerves also give rise to an internal 

 branch, which passes inwards and joins again with the 

 stomatogastric to form a large ganglion. Behind this 

 ganglion the stomatogastric nerve bifurcates. Each 

 branch, which is known as the posterior gastric nerve 

 (p. </./!.), passes backward to the pyloric fore-gut. Here 

 the two nerves join again, thus forming a ring. From the 

 posterior end of this ring three nerves are given off — one 

 to the hind-gut (n. /.), one to the digestive gland (n. I.) and 

 one to the integument (n. t.). The muscles in this region 

 of the fore-gut are also innervated from the posterior 

 gastric nerves. 



The postero-lateral nerve (p. n.) of each side arises 

 from the inner side of the commissure, immediately 

 behind the paroesophageal ganglion. It passes backward, 

 and innervates the posterior dilator muscle of the 

 oesophagus. It then passes upward along the posterior 

 wall of the fore-gut, and supplies the muscles in this 



region. 



Sense Oegans. 



The Eye. 



Each eye is situated at the distal extremity of the 

 long optic peduncle. The peduncle is clearly divided into 

 two portions: — (1) A long narrow proximal part, which 



