30 



second (PI. II., ant. 2). These lobes are continued back- 

 wards as large nerves, wbich. pass one on each side of the 

 oesophagus, forming the pericesophageal nerve ring (PI. 

 II., 'peri. n. /-.). 



The mouth parts are not innervated from a single 

 pair of post-oesophageal ganglia. Immediately behind 

 the oesophagus, the main nerves give olf ventrally a pair 

 of branches passing to the mandibles, after which they 

 unite, forming the first pair of post-oesophageal ganglia, 

 from Avhich a pair of branches innervate the first maxillae 

 (PI. II). Separating slightly, the m.ain nerves become 

 drawn out from above downwards, and, giving off later- 

 ally a pair of very small nerves which pass to the body- 

 wall, they re-unite to form a large pair of ganglia, from 

 which a pair of branches run down to the second maxillae. 

 Between this and the third pair of post-oesophageal 

 ganglia the nerve cords again separate, giving off dorsally 

 a pair of fine nerves, which run upwards and backwards 

 to the point of origin of the hepato-pancreatic tubes 

 (PI. II., /;. p.). The third post-oesophageal ganglion 

 (PI. II., jj.g. 3) is four-lobed, the lower two lobes being 

 continued into a large pair of nerves which pass first 

 backwards and then downwards and forwards to the 

 maxillipeds. The upper pair separate and pass back to 

 form the double ventral nerve chain of seven thoracic 

 and four abdominal ganglia. 



Between each pair of ganglia in the ventral chain 

 and the next the nerve cords separate and give off a pair 

 of branches which innervate the longitudinal muscles of 

 the body-wall connecting one segment with the next (PL 

 II., n.c). From each pair of ganglia, except the fourth 

 abdominal one, two pairs of branches arise, the anterior 

 pair small and non-ganglionated, the posterior large and 

 ganglionated. The latter pass to the appendages, the 



