SOUND RECEPTION 89 



As Gray (1960) pointed out for Locust a, displacement of the 

 membrane is presumably transmitted to the cap cell. The cap appears 

 to be rigidly seated on the scolopale, which in turn seems to be firmly 

 locked to the dendrite. The cilium-like tip of the dendrite lies freely in 

 the extra cellular cavity of the scolopale and cap. What moves in 

 respect to what is obscure. Now that the electron-microscope is 

 revealing more clearly the structural relationships of these sensilla, 

 earlier speculations upon their mode of action based upon the partial 

 knowledge provided by the light microscope have only historical 

 value. 



Function - Orthoptera 



The earliest attempt to analyse thoroughly the function of tympanic 

 organs was that of Regen (1908, 1912, 1913, 1914 a, 1914 b, 1924, 1926). 

 As experimental animals he employed the cnckti Liogryllus campestris 

 and the long-horn grasshopper Thamnotrizon apterus. He demonstra- 

 ted that females would orient to a telephone transmitting the sound of 

 a male in another room and that two males could sing in concert. 

 Between the Vorspiel (prelude) and the Nachspiel (coda) of the duet, 

 that is, the beginning and end, where the two were in synchrony, there 

 was almost always an intermediate period during which the chirps of 

 the two alternated regularly. Furthermore, naive (newly moulted 

 adults) males could be induced to sing in concert with many kinds of 

 artificial sounds ranging in frequency from i 400 c/s to + 28,000 c/s. 

 All of these experiments proved that the insects were sensitive to air- 

 borne sound. When both tympanic organs were amputated the res- 

 ponses were almost completely abolished (some residual sound 

 perception remained), thus proving that the tibial tympanic organs 

 were the principal sound receptors. 



These conclusions were confirmed a few years later, when Wever 

 and Bray (1933) recorded nerve activity in the forelegs of crickets 

 {Gryllus assimilis) and tettigoniids {Amblycorypha oblongifolia and 

 Pterophylla camellifolia) by means of electrodes inserted therein. The 

 frequency range for crickets was 300-8,000 c/s; for the tettigoniids, 

 800-45,000 c/s. The electrical response was asynchronous at all fre- 

 quencies. These experiments alone were not conclusive, because, by 

 inserting their electrodes into the leg rather than directly upon the 

 tympanic nerve, Wever and Bray might conceivably have been record- 

 ing from tactile hairs and other chordotonal organs of the leg as well as 

 from the tympanic organ (cf. also Wever, 1935). An attempt to 

 circumvent these difficulties was made with Decticus by Antrum 



