A UDITOR Y AND SO UND-PROD UCING MECHANISMS. 601 



Miiller's organ both in form and structure ; it is situated on 



the tracheal sac beneath the tympanic membrane. The crista 



consists of a ridge which extends from the bulb, in a longitudinal 



direction, over the sac. This ridge is formed of cuboid cells 



which become smaller as they recede from 



the bulb. These cells enclose the enlarged 



capitella of the chordotonal threads. The 



chordotonal ligaments extend from the 



cuboid cells to the adjacent integument. 



The ligaments are longest at the proximal 



end of the crista, that nearest to the bulb, 



and become gradually shortened as they 



approach the distal end of the crista. The 



chordotonal rods are frequently bent at right 



angles, where they join the capitella, and are 



sometimes jointed in the middle. 



The Supratympanic Organ (Graber's organ) 

 (Fig. 78) resembles a large Miillerian organ, 

 which is fan-shaped in section. It is at- 

 tached to the integument, near the tympanic 

 membrane, and lies upon a ganglion, in which 

 a branch of the auditory nerve terminates. 

 It is only indirectly connected with the tym- 

 panic membrane and its air-sac through the 

 medium of the circulating fluid ; it lies in a 

 distinct blood sinus, one of the walls of 

 which is formed by the tracheal air-sac. 



The Mirrors of the Locustidae are thin, tense 

 areolas of a circular form, situated on the 

 base of the elytra of the sound-producing 

 males. They are usually regarded as organs 

 for the intensification of the sound produced 

 resonating organs. This view of their nature is rendered 

 more probable since these insects possess ear-like organs on 

 the anterior tibiae in both sexes. 



The Mirrors and Tymbals of the Cicadae are situated in 

 special cavities on the sides and below the base of the 



FIG. 77. The crista 

 and tympanic (Sie- 

 bold's) organ of 

 Ephippigera vitiiun, 

 Serv., after Graber 

 [283] : tr, the bulb 

 of the crista acous- 

 tica ; at, pt, an- 

 terior and posterior 

 tympanic m e m- 

 branes ; n, auditory 

 nerve. 



