322 THE WINGS OF LEPIDOPTERA 



color is given by Professor Tower in his Colors and Color-patterns of Coleop- 

 tera (Tower '03). 



Following the classification of Tower the colors of the scales of the 

 Lepidoptera may be either chemical, physical, or chemico-physical. The 

 chemical colors are produced by pigments in the scales; the physical colors 

 are produced either by reflection, refraction, or diffraction of light ; and the 

 chemico-physical colors are produced by either a reflecting, refracting, or 

 diffracting structure overlying a layer of pigment. There are also what 

 Tower calls combination colors due to a combination of the causes just 

 mentioned. 



As the production of colors by pigments is the most obvious method in 

 nature, it is the one to which the colors of the Lepidoptera are commonly 

 attributed. But it is now well-known that a large proportion of the most 

 beautiful colors of these insects are either physical or chemico-physical; 

 this is true of the various metallic and iridescent colors so commonly found 

 in butterflies and many moths. 



Explanations of the methods of production of physical colors are given 

 in text books on physics; it is, therefore, only necessary here to point out a 

 feature in the structure of the scales of Lepidoptera that results in the pro- 

 duction of these colors. This feature is the presence of the fine longitudinal 

 striae described above. When the striae are very fine and close together 

 they act in the same way as does a diffraction grating, producing the beauti- 

 ful iridiscent colors. Kellogg ('94) found that on certain scales from a 

 species of Morpho the striae were from .0007 mm. to .00072 mm. apart or at 

 the rate of about 35.000 to the inch. 



The fact that certain colors are due to the way in which light is reflected 

 from the scales can be shown by the following experiment. Place on the 

 stage of a microscope the wing of a bright blue butterfly, and shade the 

 specimen so that it is viewed only by transmitted light from the mirror of 

 the microscope; when examined in this way the blue color will be absent. 

 This is due to the fact that the light passing directly through the scales is 

 not broken up and only the colors produced by pigment are visible. 



There is still another function of the scales of Lepidoptera; they may 

 serve as the outlets of scent glands. As the scales that serve this purj^ose 

 are found chiefly on the wings of males, they have received the special name 

 of androconia, signifying male dust. 



Androconia are most readily found in the "brand" of the wings of males 

 of the subfamily Pamphilinas, the skippers with a discal patch ; in the costal 

 fold of males of the Hesperiinae, the skippers with a costal fold; and in the 

 discal patch of the wings of certain Lycenidas, the blues. They occur, 

 however, in many other situations. 



The androconia are of various shapes (Fig. 332); they are frequently 

 fringed at the distal end, with each tip of the fringe finely divided. This is 



