OF INSECTS. 175 



nerves in pairs, which visit all the principal organs ; 

 and ramify in all directions. 



The nervous system may be considered under two 

 divisions, theganglionic central cord, with its branches, 

 and the nervous system of the esophagus and stomach. 

 The former is the analogue of the spinal marrow, 

 and the latter of the great sympathetic nerve. 



The ganglionic cord extends from the head to the 

 hinder extremity, is situate beneath the intestinal 

 canal, and runs along the ventral face of the body ; 

 (PI. II. fig. 1, g, h, i, I, /.) This presents knotty 

 expansions or ganglia at intervals throughout its whole 

 course. Two of these are placed in the head, one 

 above the esophagus near the pharynx, the other 

 beneath it, and, considered collectively, they form 

 what many authors have denominated the brain, 

 (cerebrum and cerebellum of Burmeister.) The an- 

 terior of these cephalic ganglia, (the cerebrum,) lies 

 transversely, and is usually more or less distinctly 

 divided into two hemispheres. It emits a nerve to 

 each of the antennae, also the optic nerves, and lateral 

 branches which unite it to the posterior cephalic 

 ganglion. The optic nerves spring from the outer 

 margin of each cerebral lobe, and are generally broad 

 at the base and narrower at the extremity terminating 

 in the eye. Their base is sometimes as wide as the 

 lobes themselves, and in certain cases they are broader 

 at the extremity than any part of the cranial ganglion. 

 The optic nerves of the stemmata likewise originate 

 from the same source, sometimes in single filaments, 

 at other times divided near the extremity. After the 



