98 THE ANIMAL KINGDOM. 



SCALES OF THE SILKWORM MOTH. 



The Silkworm Moth (Bombyx mori), has a variety of 

 scales, toothed, and broad or narrow, and Leuwenhoeck 

 reckoned no less than 400,000 of these delicate scales on 

 the wings of one moth. 



SCALES OF CLOTHES MOTH. 



From the under side of that troublesome little Tinea we 

 obtain a beautiful test object of very fine striae. Also from 

 the Podura. 



SCALE OF PODURA. 



The Podura is a small gray wingless insect, with six legs, 

 and a long forked tail, bent inwards, and by means of which 

 it leaps and springs about in the sawdust of our cellars, and 

 under stones, and in moss in damp places. 



SCALES OF LEPISMA SACCHARINA. 



A first cousin of Podura, haunting our sugar stores, and 

 originally a native of America. It does not leap so well as 

 Podura, if at all ; for its body does not terminate in a forked 

 tail, but in several long thread-like styles, and it runs 

 swiftly along, the little silvery gray body closely covered 

 with these beautiful scales, which require high and good 

 powers to see distinctly. 



A few words may be added on the appearance which 

 Podura scales should present as a test object. Under a 

 medium power they resemble watered silk ; light and dark 

 lines wave across the scale in irregular bands; but with 

 better definition every dark band should be resolved into 

 rows of short lines, thick at one end, and very fine at the 

 other. Yet these apparent lines are not lines. "We must 

 have a higher power, a good quarter-inch lens, and then 

 with careful management of light, always a most impor- 

 tant thing, we shall see that the apparent lines are really 

 spaces between the wedge-like particles which make up 

 the layer or upper surface of the scale. As a test object it 

 is out of fashion ; the dots of the Pleurosigma and the striae 



