ANATOMY AND PHYSIOLOGY 107 
proved by the well-known experiments of Mayer. He fastened 
a male Culex to a microscope slide and sounded various tuning 
forks. Certain tones caused certain of the antennal hairs to 
vibrate sympathetically, and the greatest amount of vibration 
occurred in response to 512 vibrations per second, or the note 
C”, which is approximately the note upon which the female 
hums. The male probably turns his head until the two an- 
tennz are equally affected by the note of the female, when, by 
Inner aspect of right tympanal sense organ of a grasshopper, Caloptenus italicus. 
b, chitinous border; c, closing muscle of spiracle; 
nerve; 0, opening muscle of spiracle; p, p, processes resting against tympanum; s, 
spiracle; im, tensor muscle of tympanum; v, vesicle.—After GRABER. 
gn, ganglion; m, tympanum; 1, 
going straight ahead, he is able to locate her with great 
precision. 
In the lack of experimental evidence, other organs are in- 
ferred to be auditory on account of their structure. Acridiidee 
bear on each side of the first abdominal segment a tympanal 
sense organ—the subject of Graber’s well-known figure (Fig. 
137). This organ is admirably adapted to receive and trans- 
mit sound-waves. The tympanum, or membrane, is tense, 
and can vibrate freely, as the air pressure against the two sur- 
