Chap. VI.] ^lERVOUS SYSTEM OF ARTHROPODS. 103 



would, of course, be of importance to any organisms, but 

 more especially to those possessing active powers of loco- 

 motion. They would serve, on the one hand, to assist in 

 bringing their possessors into relation with food, or with 

 sexual mates, and, on the other, to warn them of the 

 approach of enemies. 



The nervous system of Insects varies not only among 

 different classes and orders, but even in the same indivi- 

 dual in different stages of its development. The cater- 

 pillar of a Moth (fig. 39) or Butterfly presents a nervous 

 system not very different from that met with in the 

 Centipede; \^jhile in the imago 

 or perfected Insect, the same 

 system has undergone some re- 

 markable changes — there is, for 

 instance, an increased size of 

 the cerebral ganglia, and also a 

 notable development of some of 

 the ganglia pertaining to the 

 ventral cord, while concentra- 

 tion or even suppression of 

 others is met with. 



1 • 1 -r> J.J. Fig. 42.— Brain and Adjacent Parts 



in such m sects as Butter- of Nervous System of a rather 



flies. Bees, Dragon-flies, and '^""ssi^^' ^pt«^°^« ^l'\^^' 3;;^"'«^-^''« 



' ' ° ^ tenebricosa. (iNevrport.) a, Bram re- 



OtherS where the visual organs ceMng the antennal nerves, and also 



, T 1 T ;i B, the optic nerves ; c, origin of the 



are enormously developed, and ,y ^ipathetic from and rear the com - 



in which the power of vigorous mencement of the ^bophageal cords ; 



*■ , . D, the sub-ojsophageal ganglia; 6, the 



and sustained flight is COrreS- vagus, or visceral nerve before reach- 



pondingly increased, the nervous '-^ ''^ ^'-^^i^"' '' '^''''' ''''''''' 



r n .J ' nerves. 



system as a whole attains its 



maximum of development among the Arthropoda. The 

 brain of these creatures difl'ers from that existing in all 

 other members of the class by reason of the great develop- 



