304 



INSECTA. 



their number is still further reduced (Jig. 138, c); their size, in the 

 thorax especially, considerably increased ; and the brain, now ar- 

 rived at its maximum of developement, is furnished with the won- 

 derful apparatus of eyes and other instruments of the senses, 

 which heretofore would have been absolutely useless, but now, with 

 the expansion of the brain, have become suited to the more ex- 

 alted faculties of the insect. 



Fig. 138. 

 B C A 



Many insects are capable of producing audible sounds ; and some- 

 times the noises they make are exceedingly shrill, and may be heard 

 at some distance. Such sounds originate from various causes in 

 different tribes, and it is not always easy to detect the mode of 

 their production. In many beetles they are caused by rubbing 

 different parts of their dense integument against each other, and 

 the chirping of several Orthoptera seems to have a similar origin ; 

 the acute note that these insects utter is apparently produced by 

 friction, the edges of their hard pergamentaceous wings being 



