4(38 PHYSIOLOGY. 



either their legs together or against the body. Bugs also (viz. Cime.r 

 [Reduvius~\ sulapterus, De Geer*) and the Mutillee (M. Europcea) 

 produce such sounds upon being touched f, the former by the motion 

 of its head, probably, therefore, by rubbing the occiput against the 

 margin of the prothorax. 



Hence, consequently, all these sounds are doubtlessly expressions 

 of pain or displeasure, precisely as many of the higher animals only 

 under similar circumstances make their voices heard, but have otherwise 

 no use for them. 



270. 



The second kind of sounds which insects produce are those which 

 we hear during their flight, and especially by the Hymenoptera and 

 Diptera, but also by the beetles, Orthoptera, and bugs. That these 

 sounds are not produced solely by the napping of the wings, we may 

 easily convince ourselves, for if the wings be cut off, the fly produces 

 its former sound, although somewhat weaker. Hence, therefore, the 

 question occurs, Which is truly the organ of sound ? The reply will 

 readily suggest itself when we shall have first more closely investigated 

 the conditions under which the noise originates. If any fly, for instance, 

 the very common Eristalis tenax, be held by the legs, and the wings 

 left free, it will endeavour by the violent motion of its wings to 

 emancipate itself, and emits a loud buzzing sound. If the wings be 

 half cut off, the vibration of the wings continues, and the sound becomes 

 shriller ; but if they be quite cut off, we observe their roots still in 

 motion, and the sound becomes a little shriller, but also weaker than 

 before. Thus, therefore, the presence of the wings has no influence 

 upon the production of the sound, and at most but a trifling one in 

 causing a change of tone. But there are other organs besides the wings 

 upon the thorax which might be the causes of the sound, namely, the 

 scales behind the wings, the poisers, and the spiracles which lie between 

 the meso- and metathorax. If the scales be removed, the sound is not 

 at all affected ; it remains unchanged as long as the wings can vibrate. 

 If the poisers, lastly, be cut off, this produces no difference of sound, 

 and a fly deprived of all the external organs which tend to assist the 

 flight, can, so long as the mere stumps of the wings remain to vibrate, 

 produce a distinct but somewhat weaker and higher sound. The 

 spiracle alone remains, therefore, to be considered as the cause and 



* Memoires, torn. iii. p. 190. f Kirby and Spencc, vol. i. 



