120 



NERVOUS SYSTEM 



CHAP. 



those great lobes of the brain that are directly connected with 

 the faceted eyes must not be taken into account in a considera- 

 tion of the relation of the size and development of the brain to 

 the intelligence of the individual. The weight of the brain in 

 Insects is said by Lowne to vary from -j-^-^ to ^5^^ ^^ ^^^ 

 weight of the body. 



Figure 65 gives a view of one side of the supra-oesophageal 

 ganglion of the worker of an ant, Formica rufa, and is 

 taken from Leydig, who gives the following elucidation of it : 

 A, primary lobe, a, homogeneous granular inner substance, l, 

 cellular envelope ; B, stalked bodies (gyri cerebrales), a, h, as 

 before ; c, presumed olfactory lobes, c, inner substance, cl, gang- 



FiG. 66. Stomato - gastric 

 nerves of Cockroach : A, 

 with brain in situ, after 

 Koestler ; B, with the 

 brain removed, after Miall 

 and Denny : s.g, supra- 

 oesophageal ganglion ; o, 

 optic nerve ; a, antennary 

 nerve ; f.g, frontal gang- 

 lion ; oe, oesophagus ; c, 

 connective ; p.g, paired 

 ganglia ; v.g, crop or ven- 

 tricular ganglion ; r, re- 

 current nerve. 



lionic masses ; D, ocular lobes, e, /, g, h, various layers of the 

 same ; e, origin of lateral commissures ; F, median commissure 

 in interior of brain ; G, lower brain (sub-oesophageal ganglion) ; 

 H, ocelli; /, faceted eye. 



Besides the brain and the great chain of ganglia there exists 

 an accessory system, or systems, sometimes called the sym- 

 pathetic, vagus, or visceral system. Although complex, these 

 parts are delicate and difficult of dissection, and are consequently 

 not so w^ell known as is the ganglionic chain. There is a con- 

 necting or median nerve cord, communicating with the longi- 

 tudinal commissures of each segment, and itself dilating into 

 ganglia at intervals ; this is sometimes called the unpaired 

 system. There is another group of nerves having paired ganglia, 



I 



