84 EVENINGS AT THE MICROSCOPE. 



These gems are flat transparent scales, very regularly 

 oval in form, for one end is rather more pointed than the 

 other ; there is no appearance of a foot-stalk, and by what 

 means they adhere, I know not ; they are evidently at- 

 tached in some manner by the smaller extremity to the 

 velvety black surface of the wing-case. The gorgeous 

 colours seem dependent in some measure on the reflection 

 of light from their polished surface, and to vary according 

 to the angle at which it is reflected. Green, yellow, and 

 orange hues predominate ; crimson, violet, and blue are 

 rare, exoept upon the long and narrow scales that border 

 the junctions of the wing-cases, where these colours are 

 the chief reflected. Yet there appears to be some positive 

 colour in their substance ; for in these latter scales, which, 

 projecting beyond the edge of the wing-case, can be ex- 

 amined as transparent objects, and that with a high 

 power, the transmitted light is richly coloured with the 

 same tints as the same scales displayed under the Lieber- 

 kiihn. 



We may derive pleasant instruction from continuing our 

 observations on a few other wings of insects. If you have 

 ever thought on the subject, you have probably taken for 

 granted that the various sounds produced by insects are 

 voices uttered by their mouths. But it is not so. No 

 insect has anything approaching to a voice. Vocal sounds 

 are produced by the emission of air from the lungs, 

 variously modified by the organs of the mouth. But no 

 insect breathes through its mouth ; no air is expelled 

 thence in a single species ; it is a biting, or piercing, 

 or sucking organ ; an organ for the taking of food, or an 

 organ for offence or defence ; but never an organ of 

 sound. 



The wings are in most cases the immediate causes of 

 insect sounds ; and, in the case of the Two-winged Flies 

 (Diptera), Kirby seems to have shown on sufficient evidence 

 that the humming is produced by the friction of the root or 



