144 THE SENSE ORGANS AND REFLEX BEHAVIOUR 



of tympanal organs near the proximal extremity of the tibia of 

 each fore leg. 



In the Cicadidfe tlie j)resume(l absence of any receptor organs 

 for sound vibrations had for many years been an outstanding 

 difficulty in interpreting the function of their highly de\'eloped 

 powers of sound production. It was not until 1923 that Vogel, 

 in Germany, proved on histological grounds that true tympanal 

 organs are present in both sexes of these insects. In the male the 

 cavity beneath the operculum of the sound-producing organ is 



bounded posteriorly by a struc- 

 ture commonly termed the 

 mirror. The latter organ had 

 long been claimed to be a 

 resonator, and it remained for 

 V\)gel to show that it is the 

 tympanum ^ of an auditory organ. 

 The true })ercipient part of this 

 organ consists of a group of an 

 immense number (about 1,500) 

 Fig. G1. Hori/.ontal section across of chordotonal sensillae stretching 

 portions of thorax and abdomen of across the cavity of what may 



thr°TgM Tnd- Tff'VSl be tern.ed the auditory capsule", 



organs, at, Accessory tympanum ; At one of their extremities these 

 d, chitinous lamella ; /, ligament -ii attached bv Haa- 



supporting chordotonal organ ; n, ^ensuia" are attacnea, D\ liga 



chordotonal nerve ; t, tympanum ; mentous prolongations, to a 



tc, right tympanic chamber. „„^- ,-]„„ ..^ocess connected with 

 (Adapted from Eggers.) cuticuiai process connected witn 



the mirror or tympanum. At 



their other extremities the sensillse are attached to the outer 



wall of the auditory capsule. In the female the tympammi is 



also well developed but somewhat reduced in size. 



In many Lepidoptera highly developed tympanal organs are 



also present. The comprehensive studies of Eggers (1919, 1928) 



have shown that these structures are present on either side of the 



^ Swinton, as long ago as 1877, gave reasons for concluding that the so-called 

 mirror was tlie tympanum of an auditory organ. As is pointed out by Myers 

 in his book on Cicadas (1929), this account had been long overlooked, and 

 Vogel only discovered Swinton's paper when his own detailed studies were 

 Hearing completion. 



