66 THE MICROSCOPE. 



matter which it is impossible to do from the appearance of 

 the markings in their unaltered state : 



" Eemove 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 prevented from moving 

 by a little paste at each corner. No. 3 may then be taken 

 as an exaggerated section of the various parts. AB is the 

 glass slide, with a scale, (7, closely adherent to it, and D 

 the thin glass cover. If a very small drop of water be 

 placed at the edge of the thin glass, it will run under by 

 capillary attraction ; but when it reaches the scale, (7, it 

 will run first between it and the glass slide A B, because 

 the attraction there will be greater, and consequently the 

 markings on that side of the scale which is in contact with 

 the slide will be obliterated, while those on the other side 

 will, for some time at least, remain unaltered : when such 

 is the case, the strongly marked vertical lines disappear, 

 and the radiating ones become continuous. (See No. 1, 

 the lower left hand portion.) To try the same experiment 

 with the other, or inner surface of the scales, it is only 

 requisite to transfer them, by pressing the first piece of 

 glass, by which they were taken from the insect, upon 

 another piece, and then the same process as before may be 

 repeated with the scales that have adhered to the second 

 slide ; the radiating lines will now disappear, and the ver- 

 tical ones become continuous. (See No. 2, left portion.) 

 These results, therefore, show that the interrupted appear- 

 ance is produced by two sets of uninterrupted lines on 

 different surfaces, the lines in each instance being caused 

 by corrugations or folds on the external surfaces of the 

 scales. Nos. 1 and 2 are parts of a camera lucida drawing 

 of a scale which happened to have the opposite surfaces 

 obliterated in different parts. No. 4 shows parts of a 

 small scale in a dry and natural state ; at the upper part 

 the interrupted appearance is not much unlike that seen 

 at the sides of the larger scales, but lower down, where 

 lines of equal strength cross nearly at right angles, the 

 lines are entirely lost in a seriee of dots, and exactly the 

 same appearance is shown in No. 5 to be produced by two 

 scales at a part where they overlie each other, altnough 

 each one separately shows only parallel vertical lines." 



