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- 



-^-— 5J\ 



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 (f), about the oesophagus, from the 

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

 system {f) 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-Iateral 

 parts of the wide and straight alimentary canal. 



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

 thick subocsophageal or ventral chord {i, i), to supply the confluent 

 maxillae, which form the under lip : the nerves of the two single 

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



