92 TRUE TALES OF THE INSECTS. 



level with the skin, surrounded by a simple horny ring ; 

 or it may be somewhat depressed, a portion of the 

 segment projecting a little over it ; and sometimes it is 

 very sunken in the abdomen, the arched and horny sides 

 projecting over it so much that nothing is seen exter- 

 nally save a sort of slit with a cavity or pit beneath it. 

 In the last condition the organ exists in the genera 

 Mecostethus and Stenobothrus, which are among our 

 native grasshoppers. It is usually conceded that this 

 ear consists of a tympanum supplied internally with an 

 auditory nerve and a ganglion, besides muscles, and 

 tracheal apparatus ; it is undoubtedly a sense-organ of 

 an extremely delicate nature. It is found in both sexes, 

 as in most of the species of Acridiidae. The forms in 

 which it is absent are generally at the same time wing- 

 less, and destitute of organs for producing special sound. 

 Yet to decide as to the exact function of these ear- 

 like acoustic organs is a matter of extreme difficulty. 

 We know, from the fact that the insects are easily 

 disturbed, that the sense of hearing must be delicate, 

 and the Acridiidse with ears are believed to be sensitive 

 to sounds by means other than these organs. This 

 suggests that the purpose of the latter is the perception 

 of special sound. What can this be ? Is it the fiddling 

 or stridulating sound which we have seen they produce ? 

 Any insect having elaborate sound-producing organs 

 must be supposed to have ears to hear the sound 



