ERRORS OP INTERPRETATION. 



65 



of the object. An instance of this is furnished in an 

 examination of the scales of Lepisma saccharina. 



" Upon the more abundant scales the most prominent 

 markings appear as a series of double lines, which run 

 parallel and at considerable intervals from end to end of 

 the scale, whilst other lines, generally much fainter, 

 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 appearance at the 

 sides of the scale which is very different from the mere 

 union, or ' cross-hatchings,' of the two sets of lines." 

 (Fig. 37, Nos. 1 and 2, the upper portions.) 



Fig. 37. Portions of Scales of Lepisma, after Beck. 



The scales themselves are formed of some truly trans- 

 parent substance, for water instantly and almost entirely 

 obliterates their markings, but they reappear unaltered as 

 the moisture leaves them ; therefore the fact of their being 

 visible at all, under any circumstances, is due to the refrac- 

 tion 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 



