INSECTS 



lying against the 

 lower wall of the 

 first body seg- 

 ment (Fig. 72, 

 Gng 1), which is 

 likewiseconnect- 

 ed with a fourth 

 mass in the sec- 

 ond segment, and 

 so on. The cen- 

 tral nervous sys- 

 tem of the insect 

 thus consists of 

 a series of small 

 nerve masses 

 united by double 

 nerve cords. The 

 nerve masses are 

 known as gan- 

 glia {Gng), and 

 the uniting cords 

 are called the 

 connectives (Fig. 

 71, Con). Typi- 

 cally there is a 

 ganglion for each 

 of the first 

 eleven body seg- 

 ments, besides 

 the brain and 

 the lower gan- 

 glion of the head. 

 The brain of an insect (Fig. 71) has a highly complex 

 internal structure, but it is a less important controlling 

 center than is the brain of a vertebrate animal. The other 

 ganglia have much independence of function, each giving 

 the stimuli for movements of its own segment. For this 



r 1 



1 -* 



\^ 



iBr 



^ J 



Q 



_ _T- 



A.ntNv^ 



I 





f 



2 Br 

 jBr 



RNv 



/ 



-J; 



ol 



FrGng- 



FrCon 



fi 1 



Vm^ 



r 



i 



,/ 



IX 



1 V 



1 



]\, . CceCon. 



iX 



J V 



f> 



v\ 







^^yffiX 



a 



7 



LmNv.. > 



J « 

 i 



W''< 



V\ 



MxNv_ 



LbNv-i 



MdNv 



jllj^y-i •SixGng- 



Fig. 71. The nervous system of the head of a grass- 

 hopper, as seen by removal of the facial wall 

 AntNv, antenna! nerve; /Br, sBr.jBr, the three parts 

 of the brain; CoeCon, circumoesophageal connectives; 

 jCom, suboesophageal commissure of the third lobes 

 of the brain; FrGng, frontal ganglion; FrCcm, frontal 

 ganglion connective with the brain; LbNv, labial 

 nerve; LmNv, labral nerve; MdNv, mandibular nerve; 

 MxNv, maxillary nerve; 0, simple eye; OpL, optic 

 lobe connected with the brain; RNv, recurrent nerve; 

 SoeGng, suboesophageal ganglion 



118 



