July— AiiKii^t 1S83.] 



PSrCHE. 



parent body is converted into a 

 transparent one, and a mirror, which, 

 whatever be the materials of which it 

 is made, if approximately perfect has a 

 silverv appearance from the amoiDit of 

 reflected light, is rednced to a slightly 

 reflecting surface. But let tiie scale dry 

 again from its bath, as Fischer apparently 

 did not do, and the mirror will again 

 appear. Both silvery and milk-white 

 colorations are then onlv optical eflects 

 produced by reflected light. 



Still another kind of appearance is 

 seen in the scales of Hoplia and of 

 Entiiniis. These scales are brilliantly 

 colored, yet their color is in the one 

 case entirely lost, in the other case 

 greatly changed by wetting with almost 

 anv liquid, but when redried the colors 

 reappear with all their previous brillian- 

 cy. This coloration also resists all 

 forms of bleaching. It must therefore 

 be produced by some decomposition of 

 light. Whatever acts upon the light 

 must be within tiie scale, not upon the 

 outside, for all those scales which 

 remain perfecth' sealed, so that the 

 !ic[uid does not enter them, retain their 

 color even surrounded by liquid. This 

 proves that the color is not due to 

 external striation, where such exists. 

 The finer striation of the scales of 

 Eiitimus is evidently internal, from its 

 relations to the difterently colored 

 internal cavities of the scales. Besides 

 this striation the interior of the scale 

 is evidently filled with a pitli-like 

 substance into which liquids enter 

 with equal readiness in all directions ; 

 this pith-like portion apparently has 



some direct influence upon the produc- 

 tion of the coloration, for yvherever 

 it is injured or has shrunk away from 

 the basal end of a scale there is no 

 longer coloration in that place. Perhaps 

 it is a necessary filling to cause the striae 

 to refract the light, the same as air- 

 cavities are necessarv as a backing to 

 produce the silvery color in the scales 

 of lepidoptera. The striae themselves 

 are very fine, but yvhether they are the 

 causes of color is hard to determine 

 without more accurate instrinnents of 

 measurement than I have at m\' com- 

 mand. As near as I could tleterniine 

 they are 0.0008 to 0.0009 m'"'''- apart. 

 The wave length of a ray of light from 

 Frauenhofer's A line of the spectrum is, 

 according to Willigen, .00076092 mm., 

 and the wave length at the H^ line is, 

 according to tlie same autlKjrity, 

 0.00039713 mm. ; the difference being 

 0.00036379 mm., or the difl'erence j^f 

 wave length between violet and red 

 light. To determine the place in the 

 spectrum to which the striae of these 

 scales correspond would require, of 

 course, much finer measurements. 



The kinds of coloration of scales 

 thus far described are what Hagen has 

 termed ''optical colors." 



The second kind of coloration is 

 what Hagen terms "natural colors," of 

 which he distinguishes two kinds — der- 

 mal, where '"the pigment is deposited in 

 the form of very small nuclei in the 

 cell, or in the product of cells, in the 

 cuticula," and hypodermal, where "the 

 pigment is a homogeneous fatty sub- 

 stance, a kind of dye somewhat 



