9 2 



ENTOMOLOGY 



commissures) between which the oesophagus passes. This 

 compound ganglion represents at most four neuromeres : ( i ) 

 wandibular, innervating the mandibles; (2) superlingual, 



found by the author in Collembola, 

 but not yet reported in the less gen- 

 eralized insects; (3) maxillary, inner- 

 vating the maxillae; (4) labial, which 



sends a pair f nerves to the labium - 

 The minute structure of the brain, 



though highly complex, has received 

 considerable study, but \vill not be 

 described here for the reason that the 

 anatomical facts are of no general 

 interest so long as their physiological 

 interpretation remains obscure. 



Sympathetic System. Lying 

 along the median dorsal line of the 

 oesophagus is a recurrent, or stomato- 

 gastric, nerve (Fig. 114), which 

 arises anteriorly in a frontal gan- 

 glion and terminates posteriorly in 

 a stomachic ganglion situated at 

 the anterior end of the mid intes- 

 tine. Connected with the recurrent 

 nerve are two pairs of lateral ganglia, 

 the anterior of which innervate the 

 dorsal vessel and the posterior, the 

 tracheae of the head. The ventral 

 nerve cord may include also a median 

 nerve thread (Fig. in) which gives 

 off paired transverse nerves to the 

 muscles of the spiracles. 

 Structure of Ganglia and Nerves. A ganglion consists 

 of (i) a dense cortex, composed of ganglion cells (Fig. 115), 

 each of which has a large rounded nucleus and gives off usu- 

 ally a single nerve fiber; and (2) a clear medullary portion 



Sympathetic nervous system 

 of an insect, diagrammatically 

 represented. a, antenna 1 

 nerve; b, ' brain; f, frontal 

 ganglion; /, /., paired lateral 

 ganglia; m, nerves to upper 

 mouth parts; o, optic nerve; 

 r, recurrent nerve; s, nerve to 

 salivary glands; st, stomachic 

 ganglion. After KOLBE. 



