Chap. VL] NERVOUS &YSTEM OF ARTHROPODS. 



105 



all Insects with a separate sub-oesopliageal ganglion, from 

 which nerves are given off to the mandibles, the maxillae, 

 and the labium. But, as in Spiders, the oesophageal ring is 

 often very narrow, owing to the greatly diminished size of 

 the oesophagus in the imago forms of higher Insects. In 

 Spiders and Myriapods, as before stated, the sub-oeso- 



FiG. 43. 



Fig. 44. 



Fig 45 



>^^ 



Fig. 43.— Nervous System of a White Ant ( Termes). (Gegenbauer after Lesp^s.) 



Fig. 44.— Nervous System of a Water Beetle (Dutiscus). (Gegenbauer.) 



Fig. 45.— Nervous System of a Fly (3Iusca\ (Gegenbauer after Blancbard.) o. 



Eyes ; g.% supra-oesophageal ganglia (brain) ; gi, sub-oesophageal ganglion ; yr, g'^, <j^ 



fused ganglia of tlie tliorax. 



phageal ganglion has no separate existence apart from 

 the thoracic ganglia. 



In many Insects the three thoracic ganglia preserve 

 a separate existence (fig. 43), though in others of the 

 higher types above referred to these ganglia are more 

 frequently fused into a single lobed mass (fig. 45). The 



