70 KANSAS UNIVERSITY QUARTERLY. 



rows and the scales of one row partially overlap the scales of another 

 there may be from two to eight superposed lamellae at various regu- 

 larly recurring points on the wing. These superposed scale-lamellae 

 produce colors by interference just as the familiar colors are pro- 

 duced in the case of soap-bubbles, oil-films on water, or where there 

 are other thin layers of transparent substances. 



In addition, the striee-bearing surface of the scale, being composed 

 of thickened opaque lines with transparent interspaces, is essentially 

 the same as a ruled surface or grating, producing the interference 

 phenomena of diffraction. The finest of Rowland gratings possesses 

 lines slightly exceeding looo to the millimeter. The strise of the 

 transparent scales of Micropteryx are from about 500 to 300 to the 

 millimeter, varying in different species. The opaque scales of MorpJio, 

 which show metallic reflections, have about 1400 stria; to the milli- 

 meter. 



The colors due to interference are those brilliant metallic or irri- 

 descent tints especially common among the butterflies, as in MorpJw 

 and Lyciviia. But it is rare that these interference effects constitute 

 all of the colors of a lepidopterous wing. This, however, is the case 

 in Micropteryx, where all the scales are transparent and colorless. 

 Usually the near ly transparent scales producing interference effects 

 are colored, and commonly there are both opaque and transparent 

 scales on the wing. Unless all the scales on a wing are opaque, 

 absorption colors or " natural colors " cannot be the sole color of 

 a wing. For wherever there are transparent or subtransparent scales 

 on a wing, from the uniformly laminated and striated structure of all 

 ordinary lepidopterous scales, interference effects are bound to exist. 



Tliese color effects of the scales have been a favorite subject of 

 investigation and speculation by entomologists, and a host of obser- 

 vations are recorded. Many attempts at classifying the colors, and the 

 causes of them, have been made. In a paper of much value presenting 

 the results of a detailed study of coleopterous scales, Dimmock* 

 lays much stress on the constant presence of air in the scales, as 

 influencing the color. 



It is evident that the color spots or lines can have much better 

 defined, sharper and more constant limits when the scales composing 

 the color spot or line are short, firm and plate-like than can be the 

 case when the scales are long, hair-like and flexuous. A uniform 

 arrangement of the scales would help much, also, in the formation of 

 sharp boundaries for the color-markings. 



In addition to the definiteness of color-marking possible with flat, 



*Dimmock, Geo., The scales of Coleoptera, Psyche, vol. 4, 1883, Cambridge, Mass.. 



