356 



NERVOUS SYSTEM OF ARTICULATED ANIMALS. 



the Moth being much shorter than that of the Caterpillar), 

 and that great changes have taken place in the relative sizes 



of the ganglia. The cephalic 

 ganglia, being now connected 

 with much more perfect eyes and 

 other organs of sense, are greatly 

 enlarged; the thoracic ganglia, 

 from which the legs and wings 

 are supplied, are enlarged and 

 concentrated ; whilst the abdomi- 

 nal ganglia are relatively dimi- 

 nished in size, the 7th and 8th 

 being entirely wanting. 



442. When the structure of 

 the chain of ganglia is more par- 

 ticularly inquired into, it is found 

 to consist of two distinct tracts; 

 one of which is composed of 

 nervous fibres only, and passes 

 backwards from the cephalic 

 ganglia, over the surface of all 

 the ganglia of the trunk, giving 

 off branches to the nerves that 

 proceed from them; whilst the 

 other connects the ganglia them- 

 selves. Hence, as in Mollusca, 

 every part of the body has two 



vus TSTEOP sets of nervous connexions ; one 



Fig. 185. NER- 

 VOUS SYSTEM OF 



LAR L V iGus F TRi HINX zfioSSw *^ the ce P nalic g^g 1 ^, tne 



other with the ganglion of its 



own segment. Impressions made upon it, being conveyed by 

 the fibrous tract to the cephalic ganglia, become sensations; and 

 by the influence of the conscious power, operating through 

 these same ganglia, the general movements of the body are 

 harmonised and directed. It is obvious that, as the motions 

 of an animal are chiefly guided by its sight, the cephalic 

 ganglia would have a governing influence over the rest, if 

 only from their peculiar connexion with the eyes ; but there 

 is good reason to believe that their functions are still more 

 different from those of the ganglia of the trunk, and that 

 sensation resides in them alone. The motions produced by 



