ANATOMY AND PHYSIOLOGY 9! 



innervates the antennae; and (3) the trito cerebrum, which in 

 Apterygota bears a pair of rudimentary appendages that are 

 regarded as traces of a second pair of antennae. 



FIG. 112. 



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

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



FIG. 113. 



Nervous system of the head of a cockroach, a, antennal nerve; ag, anterior lateral 

 ganglion of sympathetic system; b, brain; d, salivary duct; f, frontal ganglion; h, hypo- 

 pharynx; /, 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 sympa- 

 thetic system; s, subcesophageal ganglion. After HOFER. 



The subcesophageal ganglion (Fig. 113) is always con- 

 nected with the brain by a pair of nerve cords (oesophageal 



