38 



mesotliorax and the metatliorax (%. -JS). The sub- 

 oesophag-eal ganglion is joined to the brain by means 

 of a pair of para-oesophageal connectives, which pass 

 around and encircle the gullet, one on either side [conn.). 



The brain of Anurida arises in a similar manner to 

 that which has been found to obtain in other insects. It 

 is formed in the embryo by the fusion of the first three 

 pairs of primitive ganglia, which are termed the 

 protocerebrum, the deutocerebrum and the tritocerebrum 

 respectively (Plate VII., fig. 74). The completeil organ of 

 the adult Insect is divisible into three main regions, which 

 correspond with these primitive ganglia. They are as 

 follows : — 



(«) The protocerebrum, which is the largest division 

 of the brain, comprises the optic and proto- 

 cerebral lobes (fig. 48). The optic lobe on either 

 side gives origin to the main optic nerve (oj?. ??.), 

 and the latter sub-divides into five branches, 

 each branch supplying one of the eyes. The 

 protocerebral lobes form the greater part of the 

 brain when viewed from above. 



(h) The deutocerebrum, which is composed of the two 

 antennary lobes. From each lobe a stout nerve 

 (at. n.) passes to the antenna of its side, and on 

 nearing the apex of that appendage it divides 

 into a number of fine branches, supplying the 

 sense organs (Plate IL, fig. 22). 



[c] The tritocerebrum, which consists of the two 

 oesophageal lobes {trc. in fig. 48). From the 

 latter arise the para-oeso^jhageal connectives and 

 the nerves which supply the labrum. 



The sub-cesophageal ganglion or, more properly, the 

 sub-CBSophageal ganglionic mass, is formed by the fusion 

 of four pairs of primitive ganglia. From it arise paired 

 nerves, which supply respectively the mandibles, the 



