330 ZOOLOGY 



a slight groove. Each lobe is continued laterally into a stout 

 optic nerve, which supplies the compound eyes ; besides this it 

 gives off a nerve to the a^tenna of its own side, which branches 

 abundantly in the lamelliform segments, and a third nerve to 

 the labrum or upper Up. Two short commissures encircle the 

 oesophagus, and unite in the sub-oesophageal gangKon, which 

 also lies in the head ; this ganglion supplies nerves to each of 

 the mouth appendages, the mandibles, and first and second 

 maxillae. From the sub-oesophageal ganglion two commissures 

 pass backward, and enter the first or prothoracic ganglion, 

 which gives off nerves to the thoracic muscles and first pair of 

 legs. Close behind this is a large ganglionic mass, formed by 

 the fusion of the meso- and meta-thoracic ganglia, its double 

 origin being shown by a transverse groove (Fig. 188). This 

 compound ganglion supplies nerves to both pairs of wings, and 

 to the posterior two pairs of legs. 



The abdominal ganglia are all fused into one mass, which 

 is withdrawn into the thorax, and lies in the metathorax 

 immediately behind the ganglion of that segment ; indeed, it 

 seems as if part of the abdominal nervous system is absorbed 

 into the last-named ganglion, which is said to supply nerves to 

 the first abdominal segment ; the remaining seven pairs of nerves 

 arise from the abdominal mass, and pass backwards to their 

 respective segments, where they split into an anterior and a 

 posterior branch. 



In addition to the central nervous system, there is a 

 small sympathetic system, which consists of the following 

 parts. A pair of fine nerves arise from the supra-oesophageal 

 ganglion and fuse in the middle line, and so form a minute 

 triangular ganglion lying in the head (Fig. 188); from this 

 a median unpaired nerve passes back and forks over the crop, 

 and the branches unite into a small ganglion again. There are 

 also two pairs of minute ganglia which innervate the heart 

 and tracheal system, these are situated just behind the supra- 

 oesophageal ganglion. 



Like all other Insects the cockchafer is dioecious, and the 

 female may be distinguished from the male by having six 

 lamelliform segments in its antennae, whereas the male has 

 seven. 



