30 FIELD ZOOLOGY. 



alimentation. This sympathetic system connects with 

 the brain in the region of the cords leading to the brain 

 from the suboesophageal ganglion. A central nerve 

 also runs backward in the middle line of the thorax and 

 the abdomen, supplying with nerves mainly the spiracular 

 system, but also sending nerves to the muscles of the 

 abdomen and the thorax to some extent, making their 



Fig. 15. — Successive stages in the concentration of the central nervous 

 system of Dipt era. A, Chironomus; B, Empis; C, Tdbamis; D, Sarcophaga. 

 {Folsom, after Brandt.) 



movements partly reflex. A grasshopper's head severed 

 from the thorax remains sensitive for some time, and 

 will move when irritated. An insect with its brain 

 removed will eat and digest its food if that food be 

 brought into contact with its mouth parts. 



Those insects whose adult nervous system is least 

 differentiated, i. e., consists of one ganglion for each body 

 segment, represent the lowest type of insect life. Fusion 

 of ganglia and centralization of functions, signify advance 

 in nervous perception, and indicate higher types of insect 



