“The colors of butterflies change mostly from purple to blue, sometimes to yellow. The splendid violet color at the end of the wings of _Callosune ione_ is brought out by a combination of the natural with interference colors. Originally the scales are colored lake-red; but a blue interference color is mixed with it; hence the violet hue results. The blue tones, _i.e._ the splendid varying blue of the Morpho butterflies, Schatz claims, owe their hue less to the interference of light than to a clouded layer of scales situated over the dark ground, through which the light becomes reflected on the same. The scales of the Morphids are in reality brown, as we see by transmitted light; moreover, only the upper side of the scales sends off blue reflections—the under side is simply brown. But the blue scales of Urvilliana are also shining blue beneath; by transmitted light they appear as if clear yellow. The smaragd-green scales of Priamus show by transmitted light a bright red-orange, and the orange-yellow of Crœsus a deep grass-green.” (Schatz in Kolbe.) “Krukenberg presumes the golden-green color of _Carabus auratus_ to be an interference color. It is not changed by the interference of light, nor was he able to extract from the elytra any green pigment with ether, benzol, carbon of sulphur, chloroform, or alcohol, even after having previously submitted the elytra to the influence of muriatic acid or ammonia. Chlorophyll is not present, whether free or combined with an acid.” (Hagen.) Leydig has shown that the interference colors of the hairs of certain worms (Aphrodite and Eunice) may be produced by very small impressions in juxtaposition, which bring about the same effect as striæ. Such an arrangement occurs on the feathers of birds, _i.e._ on the necks of pigeons and elsewhere, and Hagen suggests that this kind of interference colors occurs more frequently among insects than is commonly known. At least the limbs of certain forms appear yellow, but when held in a certain position change to brown or blackish. “I know of no other explanation of this not uncommon fact on the legs of Diptera, of Hymenoptera, and of Phryganidæ.” Interference colors, he adds, may occur in the same place together with natural colors. “The mirror spots of _Saturnia pernyi_ show besides the interference colors a white substance in the cells of the matrix, which Leydig believes to be guanin. But this fact is denied by Krukenberg for the same species and also for _Attacus mylitta_ and _Plusia chrysitis_.” =Natural colors.=—These are divided by Hagen into _dermal_ (cuticular) and _hypodermal_. The dermal colors are due to pigment deposited in the form of very small nuclei in the cuticula. Hagen considers them as “produced mostly by oxidation or carbonization, in consequence of a chemical process originating and accompanying the development and the transformations of insects.”