38 ELEM ENTARY ENT( )MOLOGY 



of the esophagus, thus forming a nerve collar. The brain gives 

 off nerves to the eyes, antennae, palpi, and other sensory organs 

 of the head, receiving the sensory stimuli and controlling the coor- 

 dinated muscular movements. In a general way the brain is the 

 seat of whatever ' will ' an insect may have. The subesophageal 

 ganglion coordinates the movements of the mouth-parts, as well 

 as some bodily movements. The thoracic and abdominal ganglia 

 give off nerves to all parts of their segments, the movements of 

 which they control. They are more or less independent, each 



li 



FIG. 43. Nervous system of head of cockroach 



<7, antennal nerve ; ag, anterior lateral ganglion of sympathetic system ; />, brain ; d, salivary 

 duct ; f, frontal ganglion ; /i, hypopharynx ; /, labrum ; //, labium ; ;;z, mandibular nerve ; m.r, 

 maxillary nerve ; /, nerve to labrum ; ;///, nerve to labium ; o, optic nerve ; oc, esophageal 

 commissure ; oe, esophagus ; fg, posterior lateral ganglion of sympathetic system ; r, 

 recurrent nerve of sympathetic system ; s, subesophageal ganglion. (After Hofer, from 



Folsom) 



forming a nerve center for its segment. Thus a decapitated 

 insect will walk or fly, and the abdomen of a grasshopper will 

 continue to breathe, these functions being controlled by the seg- 

 mental ganglia, though lacking coordination. In addition to the 

 main nervous system there is a sympathetic system, one part of 

 which runs along the upper part of the alimentary canal and con- 

 trols the digestive process, while a small ventral sympathetic nerve 

 gives off branches which control the spiracle muscles. 



Dr. J. B. Smith, in his ' Economic Entomology," gives an 

 interesting account of some experiments which show the relation 

 of the brain and ganglia to the body : 



