Color and Pattern and their Uses 



595 



chemical (pigmenta 1 ) substances within the scale and to the structural 

 character of the scale-walls. The pigment granules within the scales are 

 brown, yellowish, or reddish, and as they mostly transmit the same colors as 

 they reflect, the colors of strongly pigmented scales are the same by trans- 

 mitted light (light shining through them) as by reflected light. But with 



FIG. 783. Diagrammatic figures showing late stages in development of scales of the 

 wing of Anosia plexippus; figure at right showing older stage than figure at left, s, 

 scale; sc, scale-cell; /, leucocyte. (After Mayer; greatly magnified.) 



the physical colors this is not the case. Scales which produce brilliant 

 blues and other colors are often empty, and these when viewed by trans- 

 mitted light are nearly colorless. Or they may contain pigment and then 

 when viewed by transmitted light show a dull brownish or yellowish color 

 entirely different from the metallic iridescence which they show by reflected 

 light. 



The physical color effects produced by scales are due to their (a) lamina- 

 tion and (6) striation. Each scale is composed of a pair of thin subtrans- 

 parent laminae (lamellae), the thin dry sides of the flattened sac, and when 

 arranged in the shingling sheath over the wing-membrane, overlapping 

 each other at sides and ends, they produce a layer of superposed thin trans- 

 parent lamellae which is exactly the structural condition necessary to the 

 production of varied refraction (interference) effects of color. This scale 

 layer produces color by virtue of its structure just as a piece of laminated 

 mica or bit of old weathered glass or film of soap-bubble produces color 

 (Newton's rings). In addition the striae-bearing outer surface of each scale 

 is essentially the same as a ruled surface or grating, producing color by 

 diffraction and interference just as do the well-known Rowland's and Ruther- 

 ford's gratings, familiar to students in physical laboratories. In the finest 

 of these artificially striated gratings the lines are about .0006 mm. apart: 

 in butterfly scales the striae are from .002 to .0007 mm. apart. 



