6o 



SMITHSOlSilAN MISCELLANEOUS COLLECTIONS 



VOL. -JJ 



the Gryllidse the tympana are exposed, but the anterior one is small 

 and more or less rudimentary and is separated from the neighboring 

 trachea by an internal chitinous plate. 



In the Tettigoniidas there are three chordotonal organs in each front 

 tibia (fig. 28). The uppermost {SgO) is known as the subgenual or- 

 gan, since it lies just below the " knee," or femero-tibial articulation. 



TmNv 



LW 



ImO 



TmO 



Fig. 28. — Chordotonal organs in the right front tibia of a Tettigoniid 

 (Decticus verrucivortis) exposed by removal of outer wall of leg (dia- 

 grammatic and simplified from figure by Schwabe, 1906). 



aTiii, anterior tympanum ; aTr, anterior tracheal branch ; Cr, crest 

 of tympanal organ; JniO, intermediate organ; LPV, wall of leg; pTm, 

 posterior tympanum; pTr, posterior tracheal branch; SCI, sense cells 

 of tympanal organ; SgNz\ subgenual nerve; SgO, subgenual organ; 

 TC, TC, tympanal cavities opening through slits on exterior of tibia 

 (fig. 29A, e, c) ; TiiiNv, tympanal nerve; TmO, tympanal organ; Tr, 

 main leg trachea. 



The second is termed the intermediate organ {ImO) because it lies be- 

 tween the upper ends of the tympana. The third is the tympanal 

 organ {TmO) or the so-called "crista acoustica " which forms a 

 crest along the outer surface of the anterior trachea, between the 

 two tympana. 



Two separate nerves enter the fore leg, according to Schwabe, 

 from the ventral ganglion of the first thoracic segment. One is the 

 usual leg nerve, the other is a special tympanal nerve. The former 

 follows the ventral wall of the leg and, in the femero-tibial articula- 



