82 THE PHYSIOLOGY OF INSECT SENSES 



unfortunately, been called a ganglion by Gray (1960). It is in fact the 

 aggregation of most of the cell bodies (of which there are 60-80) 

 of the neurons making up the sensilla. It is invested by two layers of 

 cells, one of which is the epithelium of the tracheal air sac surrounding 

 the nerve, the other being the accessory cells of the sensillum. 



Prothoracic leg tympanic organs lie in the proximal region of the 

 tibiae, one member on the anterior side, the other, posterior. They lie 



Fig. 57. Right tympanic air sac and associated structures of a noctuid as 

 seen from within the metathorax. A portion of the air sac is represented 

 as cut away to show the sensory elements. ATP, anterior tendon plate ; 

 B, Biigel; DLg, second dorsolongitudinal muscle of metathorax; 

 EP, epaulette ; L, ligament connecting chordotonal organ with scutal 

 phragma; PI, PII, pockets of tympanic frame; S, acoustic sensory 

 cells; TAS, tympanic air sac; TM, tympanic membrane; Tr, tracheal 

 twig from metathoracic spiracle. (Redrawn from Treat and Roeder 

 1959.) 



thus back to back separated by two branches of a trachea, an anterior 

 and a posterior (Fig. 55). Whereas in the Gryllidae the tympanic mem- 

 branes lie on the exposed surface of the leg, they are sunken in the 

 Tettigoniidae and are exposed to the outside only via a slit. The 

 sensilla, of which there are about seventy in each leg, lie in a long row 

 on the dorsal side of the anterior trachea. The dendrites and scolopoid 

 bodies are oriented in such a way that they are not inserted on the 

 tympanic membrane but instead on a membrane, presumably derived 



