356 



LECTURE XVI. 



consist essentially of two chords, which become separate at the lower 

 part of the pharynx : the anterior chord girts the pharynx by a trans- 



\ t J J'' 



144 



lulus. 



versely oval ring, formed by its confluence with its fellow ; the pos- 

 terior and normal columns converge at an acute angle backwards, 

 blend together, and expand into the commencement of the abdominal 

 nervous trunk ; thus inclosing the oesophagus by a second and looser 

 collar. The closer anastomotic ring is homologous with that formed by 

 the transverse commissural band of the oesophageal chords in the 

 lobster and limulus ; and probably also to the anterior nervous ring 

 discovered by Lyonnet in the Cossus ligniperda. The stomato-gastric 

 nerves which arise from the posterior part of the brain imme- 

 diately form a third slender ring {e\ about the oesophagus, from the 

 middle of the upper part of which the trunk of the stomato-gastric 

 system (y) is continued a short way back upon the stomach, when it 

 divides ; the two divisions diverge at an angle of 45°, bend abruptly 

 backwards, and run parallel with each other along the dorso-lateral 

 parts of the wide and straight alimentary canal. 



Two large nerves (A) are sent forwards from the beginning of the 

 thick subcESophageal or ventral chord (t, t), to supply the confluent 

 maxilla;, which form the under lip : the nerves of the two single 

 pairs of feet, belonging to the thoracic segments, next arise, and 



