ENTOMOLOGY IN OUTLINE STRUCTURE OF INSECTS. 



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25 



b-. 



The nervous system of insects consists of two 

 thread-like cords running the length of the 

 body, connecting which 

 are nerve centers, or gang- 

 lia. From these centers, 

 or ganglia, nerve threads 

 branch and reach all parts 

 of the body, governing the 

 sense and motion of the 

 insect. In the lower forms 

 of life the brain is a mere 

 nerve thread running 

 through the body. As we 

 advance from the lower 

 to the higher, we discover 

 small swellings or lumps 

 along this thread. These 

 are the ganglia, and each 

 one forms a separate little 

 brain, all connected with 

 the main thread. Still 

 further, we find, branch- 

 ing off from these ganglia, 

 other threads, and we have 

 a nervous system. In the 

 higher animals, the bulb 

 in the head is much the 

 larger and dominates all 

 the rest, and we know it 

 as the brain, and the rest 



as the nervous system. In the higher animals 

 there are two sets of nerves, one known as the 



matically represented, a, an- 

 tennal nerve: 6, brain, /, 

 frontal ganglion ; /, I, paired 

 lateral ganglia; ?H, nerves to 

 upper mouth parts; o, optic 

 nerve; r, recurrent nerve; 

 , nerve to salivary glands; 

 st, stomachic ganglion. (After 

 Kolbe.) 



FIG. 30. Central nervous 

 system of a thysanuran 

 (Machili*). The thoracic 

 and abdominal ganglia 

 are numbered in succes- 

 sion, a, antennal nerve ; 

 6, brain; e, compound 

 eye; I, labial nerve; m, 

 mandibular nerve; mx, 

 maxillary nejve;o, esoph- 

 agus; ol, optic lobe; ?, 

 subesophageal ganglion ; 

 sy, sympathetic nerve.' 

 (After Oudemans.) 



A 



FIG. 32. Successive stages in the concentration of the central 

 nervous system of Diptera. A, Chironomus: B, Empis; 

 C, Tabanus : D, Sarcophaga. (After Brandt.) 



