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FIRST BOOK OF ZOOLOGY. 



the manner in wliicli the various sounds emitted by insects 

 are made. It is obvious that the vibration of the wings pro- 

 duces the loud buzzing sound made by certain insects. But 

 there are other sounds which are traced directly to the 

 effect of the air rushing in and out of the spiracles, and 

 impinging on certain plates whose sharp edges border the 

 spiracle. The experiment has been made of closing the 



Fig. 91 . — Wasp sleeping while holding on to a Blade of Grass \nTH its Jaws. 



spiracles with varnish, when all noise ceased. It is believed 

 that the mosquito produces its remarkable tones in this way. 

 Such noises have always been associated with the vibration 

 of the wings, because the noise seems to be made when the 

 insect is flying, but the cause of this is explained by sup- 

 posing that the violent muscular action of moving the wings 

 also causes the air to be violently thrown out of the spiracles, 

 and as a proof of this it has been found that cutting off the 



