SOUND RECEPTION 91 



(Fig. 63). Again over the entire range the nerve response was asyn- 

 chronous. Since 10,000 c/s was the limit of the apparatus used, it would 

 appear that the tympanic organ is much more sensitive than the 

 human ear at frequencies above 10,000 c/s. In the neighbourhood of 

 3,000 c/s, according to one report of Pumphrcy and Rawdon-Smith 

 (1936 c), the tympanic organ ofLocusta exhibits maximum sensitivity. 

 At this point the frequency is only 20 db above the ear of man at its 

 maximal sensitivity. On the other hand, in an earlier paper (Pumphrey 

 and Rawdon-Smith, 1936 b) it was indicated that the threshold con- 

 tinues to fall with increasing stimulus frequency (see also Pumphrey, 

 1940). A continuous fall was observed by Antrum (1941). 



In any case, the tympanic organ is insensitive in the frequency range 

 that is optimal for man and extends into the ultrasonic range. At its 

 optimum the organ responds to a stimulus of about 7 x 10"^^ 

 ergs/sec, about the same as for man, and thus is operating at the 

 physical hmit. In contrast to the human ear, the tympanic organ of 

 Orthoptera does not fatigue readily. No diminution in the response to 

 a 2,000-c/s tone could be detected after continuous stimulation lasting 

 one-half a minute (Pumphrey and Rawdon-Smith, 1936 c). 



Although the tympanic organs are not the only receptors possessed 

 by Orthoptera (there are in addition hair sensilla and chordotonal 

 organs not associated with tympana), it is clear that they are the 

 principal, if not sole, receptors involved in detecting noises produced 

 by stridulation of the same and other species. Since Orthoptera can 

 discriminate among the various kinds of calls and can distinguish 

 between some artificial and genuine calls (Regen, 1926), it is obvious 

 that the tympanic organ does have some specialized characteristics. 



Songs of Acrididae are, on the whole, broad-band noises at 

 2-12,000 c/s with maxima at 4,000-8,000 c/s and intensities of 

 30-40 db, re 0-0002 dynes/sq. cm., at 10-30 cm. (Busnel, 1953 ; Haskell, 

 1955; Loher and Broughton, 1955). The Tettigoniidae also produce 

 wide-band noises at frequencies up to 100,000 c/s (maxima 8,000- 

 15,000 c/s) and intensities of 46-70 db (Horror, 1954; Busnel, 1953; 

 Busnel and Chavasse, 1950; Pasquinelly and Busnel, 1955; Pielemeier, 

 1946 a, 1946 b; Pierce, 1948). Gryllidae produce relatively pure tones 

 at 2,000-6,000 c/s and intensities of 40-60 db (Alexander, 1957; 

 Busnel, 1955 a, 1955 b; Haskell, 1955; Pasquinelly and Busnel, 1955; 

 Pierce, 1948). 



The songs can be described physically by five parameters: fre- 

 quency, intensity, wave form, phase, and the temporal distribution 

 of sound units (Frings and Frings, 1958). Successive units may be 



