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 

 attached 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, except 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 

 examined 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 

 Lieberkuhn. 



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 olfence 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 

 (Dipt era), Kirby seems to have shown on sufficient evidence 

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



