108 MAINE; AGRICULTURAL EXPERIMENT STATION. ICj02. 



NERVOUS SYSTEM. 



Figs. 7 and p. 



The central nervous system is concentrated. It consists of 

 five ganglia (morphologically pairs of ganglia), and a single 

 large median nerve cord which passes from the posterior end of 

 the fifth ganglion to the posterior part of the abdomen. 



The cerebral ganglion, fig. y, eg, is large and flat. It is 

 divided superficially into halves by a cleft which is deep in front 

 but shallow on the dorsal and ventral surfaces. Each half of the 

 ganglion is pointed at its anterior end. The optic tracts pass out 

 from the ganglion just posterior to these prominences. There 

 is a slight constriction where they join the ganglion. Just pos- 

 terior to the optic tract, there is on either side, a prominent swel- 

 ling, the antennal lobe, from the ventral sides of which the anten- 

 nal nerves pass anteriorly to the base of the antennae. The pos- 

 terior part of the ganglion is narrower and thinner than the 

 anterior part and is continued posteriorly over the anterior end 

 of the first ventral ganglion and the oesophagus. 



The surface of the first ventral ganglion clearly indicates that 

 it is formed by the fusion of two ganglia, the infracesophageal 

 and the first thoracic. A well marked constriction separates the 

 two. The nerves which supply the mouth parts are all given 

 off from the anterior part of the ganglion. The nerves to the 

 first pair of legs, as well as those of the muscles and other organs 

 of the prothorax are given off from the posterior part of the 

 ganglion. The nerves which go to the legs are very large, 

 and pass from the side of the ganglion, obliquely to the bases of 

 the legs. 



The second thoracic ganglion is connected with the first by a 

 broad commissure. It is much smaller than the first, nearly cir- 

 cular in outline and lies in the anterior part of the mesothorax. 

 The nerves which go to the middle legs are given off from its 

 posterior part. These nerves come from the under side of the 

 ganglion and run obliquely backward to the bases of the legs. 



The third thoracic ganglion is small, nearly round in outline, 

 and is connected with the second by a very short broad com- 

 missure. It lies in the extreme posterior part of the mesothorax, 

 and sends a large nerve obliquely backward to each of the legs 

 that are attached to the metathorax. 



