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INVERTEBRATE ZOOLOGY 



A few insects, especially larvae, live under conditions which 

 exclude the presence of oxygen. This is especially true of some 

 larvae living in very deep water. Under these conditions, 

 anaerobic respiration is carried on. 



The central nervous system consists of a brain or supraeso- 

 phageal ganglion and a longitudinal nerve chain ventral to the 

 digestive tract as in all of the Arthropoda. Typically each 

 thoracic and abdominal somite is supplied with a ganglion 



Fig. 123. — Different degrees of concentration of the ventral cord of arthropods 

 (from Gegenbauer) . A, termite (after Lespes); B, water beetle (after Blanchard); 

 C, fly (after Blanchard); D, scorpion spider (after Blanchard). a, abdomen; 

 (7^, 0^, ganglia of ventral cord; gi, infraesophageal ganglion; gs, supraesophageal 

 ganglion; o, eye; p'p'\ walking feet; tr, lung books; 1, chelicerae; 2, pedipalpi. 

 (From Hcrtwig's Manual of Zoology by Kingsley, courtesy Henry Holt and Co.). 



(Fig. 123 A). It is, however, a very common thing for the nerve 

 chain to undergo concentration as a result of which the ganglia 

 in adjoining somites fuse (B and C). The extent of such longi- 

 tudinal condensation of the nervous system varies greatly in 

 different arthropods and even shows remarkable changes during 

 the life of a single individual. Thus, in the honeybee, the larva 

 has a distinctly metameric nerve chain through the thorax and 

 abdomen but when the adult stage is reached the thoracic ganglia 

 has been reduced to two and the abdominal to five. 



A sympathetic nervous system may include a ventral trunk 

 associated with the central nervous system and some very 

 delicate branches near the dorsal part of the body. Branches 



