mSECTS : WINGS AND TUEIK APPEND A.GE8. 97 



those senera wliicli feed on ordure and carricn do 

 this. 



But the noisiest of all insects are those of the classes 

 Ortlioptera and Ilomoptera, the Crickets and Grasshop- 

 pers, and the Treehoppers. And these shall bring us 

 l>ack to our microscope, to which we shall return with 

 ihe more zest, after this little interval of repose for our 

 strained eyes. 



Listen ! we hear coming up the kitchen-stairs, the 

 Btridulous chirping of the House-cricket {Acheta do- 

 mesticd). 



" The cricket chirrups on the hearth." 



The cook shall catch us one for investigation. " Please 

 sir, here's the crickets : here's half a dozen on 'era. I 

 don't like 'em, I don't ; nastj noisy varmint !" Thank 

 vou, cook ; we'll try and turn them to some useful pur- 

 pose to-day, at least. 



Now, you see, each of the upper wings or wing-cases 

 has a clear spajce near the centre, of a triangular form, 

 crossed by one or two slender nervures. This space 

 has received the name of the tympanum or drum. It 

 is bounded externally by a broad dark nervure, which 

 with a low power we see is scored with three or four 

 longitudinal furrows, of course separated by as many 

 horny ridges. In front of the clear drum, and form- 

 ing a curved base to the triangle, there passes across 

 a horny ridge, tapering outwards, which is roughened 

 throughout its length by close-set teeth exactly like a 

 file. "When the'iusect chooses to be musical it partially 

 opens and closes its wing-sheaths, causing the two files 

 to rub across each other ; and this gives rise to the 

 peculiar ringing vibration the intensity of which is 



