74 



ENTOMOLOGY 



antennae) and converts the sensory stimuli that it receives into motor 



stimuli, which effect co-ordinated muscular 

 or other movements in response to particular 

 sensations from the environment. The brain 

 is the seat of the will, using the term ''will " in 

 a loose sense; it directs locomotor movements 

 of the legs and wings. An insect deprived of 

 its brain cannot go to its food, though it is 

 able to eat if food be placed in contact with 

 the end-organs of taste, as those of the palpi; 

 furthermore, it walks or flies in an erratic 

 manner, indicating a lack of co-ordination of 

 muscular action. 



The suboesophageal ganglion controls the 

 mouth parts, co-ordinating their movements 

 as well as some of the bodily movements. 



The thoracic ganglia govern the appen- 

 dages of their respective segments. These 

 ganglia and those of the abdomen are to a 

 great extent independent of brain control, 

 each of these ganglia being an individual 

 motor center for its particular segment. 

 Thus decapitated insects are still able to 

 breathe, walk or fly, and often retain for 

 several days some power of movement. 



In regard to the sympathetic system, it 

 has been shown experimentally that the frontal 

 ganglion controls the swallowing movements 

 and exerts through the stomatogastric nerve 

 a regulative action upon digestion. The 

 dorsal sympathetic system controls the dorsal vessel and the salivary 



FIG. 114. Sympathetic 

 nervous system of an in- 

 sect, diagrammatically repre- 

 sented, a, antennal nerve; 

 b, brain; /, frontal ganglion; 

 /, /, paired lateral ganglia; m, 

 nerves to upper mouth parts; 

 o, optic nerve; r, recurrent 

 nerve; s, nerve to salivary 

 glands; st, stomachic gang- 

 lion. After KOLBE. 



n 



FIG. 115. Transverse section of an abdominal ganglion of a caterpillar. /, nerve-fibers; g, 

 ganglion cells; n, nerve-sheath; j>, Punktsubstanz. 



