82 



ENTOMOLOGY 



trophic centers, i. e., they regulate nutrition. A nerve is always 

 either sensory, transmitting impulses inward from a sense organ; or 



A 



FIG. 114. Successive stages in the concentration of the central nervous system of Diptera. 

 A, Chironomus; B, Empis; C, Tabanus; D, Sarcophaga. After BRANDT. 



else motor, conveying stimuli from the central nervous system outward 

 to muscles, glands, or other organs. 



Functions. The brain innervates the chief sensory organs (eyes and 

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



PIG. 115. Nervous system of the head of a cockroach, a, antennal nerve; ag, anterior 

 lateral ganglion of sympathetic system; b, brain; d, salivary duct; /, frontal ganglion; h, 

 hypopharynx; /, labrum; li, labium; m, mandibular nerve; mx, maxillary nerve; nl, nerve to 

 labrum; nli, nerve to labium; o, optic nerve; oc, oesophageal commissure; oe, oesophagus; 

 pg, posterior lateral ganglion of sympathetic system; r, recurrent nerve of sympathetic 

 system; s, subcesophageal ganglion. After HOFER. 



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 



