WONDERS OF THE MICROSCOPE 243 



taken from the underside of the wing of the 

 common Wall Butterfly. It may also be said of 

 these scales that, although of almost immeasurable 



Fig. 164. Scales, or dust, from the wing of 

 a moth 



thinness, they are found to be composed of several 

 layers, plain and ornamental ; and have markings 

 of such delicacy and beauty that opticians 

 frequently use them as test-objects for obtaining 

 accuracy in microscopic lenses. 



The hairs of insects too are curious and well 



