INSECTS : WINGS AND THEIR APPENDAGES. 85 



base of the wings against the sides of the cavity in which 

 they are inserted. * 



There is a pretty little beetle (Clytus), not uncommon 

 in summer in gardens, remarkable for the brilliant gam- 

 boge-yellow lines across its dark wing-cases, which makes 

 a curious squeaking sound when you take it in hand. You 

 think it is crying; but if you carefully examine it with a 

 lens while the noise is uttered, you will perceive that 

 the cause is the grating of the thorax against the front 

 part of the two wing-cases. Several other beetles produce 

 similar sounds when alarmed, by rubbing the other end 

 of the wing-sheaths with the tip of the abdomen. Many 

 of those genera which feed on ordure and carrion do this. 



But the noisiest of all insects are those of the classes 

 Orthoptera and Ilomoptera, the Crickets and Grass- 

 hoppers, and the Treehoppers. And these shall bring us 

 back to our microscope, to which we shall return with 

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

 strained eyes. 



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

 chirping of the House-cricket (Acheta domestica). 



We will catch one for investigation. 



Kow, you see, each of the upper wings (or wing-cases) 

 has a clear space 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 longitu- 

 dinal furrows, of course separated by as many horny 

 ridges. In front of the clear drum, and forming a curved 

 base to the triangle, a horny ridge passes across, tapering 

 outwards, which is roughened throughout its length by 

 close-set teeth exactly like a file. When the insect chooses 

 to be musical, it partially opens and then closes its wing- 



* " Introd. to Entom." ; Lett. xxiv. See, however, the quotation 

 from Burmeister on p. 91, infra. 



