BECK, ON ILLUSIVE APPEARANCES. 3 
The best way to remove the scales is to press one of the 
ordinary 3 x 1 glass slides gently upon the part from which 
the scales are required, and they readily adhere to the glass, 
appearing to the naked eye like a smear of dust; under the 
microscope they present a considerable variety, not only of 
size and shape, but also in the character of their markings. 
Upon the scales that are most abundant the more pro- 
minent 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- 
hatching ” of the two sets of lines (see figs. 1 and 2, the upper 
portions). 
Fie. I. 
The scales themselves are formed of some truly transparent 
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 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 markings in their 
unaltered state :— 
