172 CALIFORNIA ACADEMY OF SCIENCES. 



suboesophageal ganglion is oval in longitudinal sections. 

 The peripheral part of each is composed of rather large 

 cells. Fibers pass from the lower ganglion through the 

 commissures to the outer anterior angles of the brain, 

 where they radiate in all directions to the peripheral cells. 

 Transverse sections of the brain of Menopon sp. (plate 

 xii, figs. 1-4, hr), followed from before backwards, 

 show in front the small, disunited sections which farther 

 back (fig. 1) become enlarged in an inner and ventral 

 direction and connected with the suboesophageal gan- 

 glion (sg) by two short, straight trunks. The latter 

 ganglion is very flat in front. Back of the commissures 

 (fig. 2) the lobes of the brain enlarge and become ovoid 

 in sections, with the large end turned inward. The 

 suboesophageal ganglion is still flattened and slightly 

 constricted in the middle. Sections passing through 

 the eyes (fig. 3) show a narrow commissure passing over 

 the pharynx connecting the previously separated cerebral 

 lobes which are now oval in shape. The suboesophageal 

 ganglion is still fiat but slightly enlarged laterally. 

 Still farther back (fig. 4) the transverse commissure 

 of the brain has increased in thickness, and the 

 subassophageal ganglion greatly enlarged, especially 

 laterally. 



The three thoracic ganglia are large, situated close 

 together, and each is generally larger than the one in 

 front. In Eurymetopus taurus each ganglion is hexag- 

 onal viewed dorsoventrally (plate xvi, fig. 7), with 

 two sides transverse, one in front and the other behind. 

 The most posterior ganglion is large and joined to the 

 mesothoracic ganglion by its anterior side. From the 

 lateral angles, which are a little back of the middle, large 

 trunks are given off to the legs, and from the posterior 

 angles larger branches, one on each side, go backwards 



