ANATOMY AND PHYSIOLOGY 1 07 



proved 1>y the well-known experiments of Mayer. He fastened 

 a male Culc.r 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- 

 tennae are equally affected by the note of the female, when, by 



FIG. 137. 



Inner aspect of right tympanal sense organ of a grasshopper, Caloptenus italicits. 

 b, chitinous border; c, closing muscle of spiracle; gn, ganglion; m, tympanum; n, 

 nerve; o, opening muscle of spiracle; />, p, processes resting against tympanum; s, 

 spiracle; tm, tensor muscle of tympanum; v, vesicle. After GRABER. 



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. Acridiidae 

 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- 



