166 



THE MICROSCOPE. 



radiate from the quill, and take the same direction as 

 the outline of the scale when near the fixed or quill 

 end ; but there is, in addition, an interrupted appear- 

 ance at the sides of the scale which is very different 

 from the mere union, or ' cross-hatchings,' of the two 

 sets of lines. (Fig, 98, Nos. 1 and 2, the upper 

 portions.) 



The scales themselves are formed of some truly 

 transparent substance, for water instantly and almost 

 entirely obliterates their markings, but they reappear 



FIG. 98. Portions of Scales of Lepisma, after Beck. 



unaltered as the moisture leaves them ; therefore the 

 fact of their being visible at all, under any circum- 

 stances, is due to the refraction of light by superficial 

 irregularities, and the following experiment establishes 

 this fact, whilst it determines at the same time the 

 structure of each side of the scale, a matter which it 

 is impossible to do from the appearance of the mark- 

 ings in their unaltered state : 



" Remove some of the scales by pressing a clean and 

 dry slide against the body of the insect, and cover 

 them with a piece of thin glass, which may be pre- 



