The faint color of the scales gradually increases in intensity. “For example, if a scale be destined to become black, it first becomes pale grayish brown, and this color gradually deepens into black.”
Urech states that in _Vanessa io_ first a white, and in _V. urticæ_ a pale reddish hue, are spread over the entire wings, and then successively arise other colors in the following order: yellow, yellow to brown, red, brown and black.
Spuler, however, claims that the differentiation of colors and markings do not follow one another, but arise simultaneously, and that his view is confirmed by Fischer. This may be the case with the highly specialized and diversely marked butterflies, but certainly taking the Lepidoptera as a whole the yellows and drabs must have been the primitive hues, the other colors being gradually added in the later more specialized forms.
It is noticeable that the most generalized moths, such as the species of Micropteryx, Tinea, Psychidæ, Hepialidæ (in general), etc., are dull brown or yellow-drab without bars, stripes, or spots of bright hues. These shades prevail in others of the more primitive Lepidoptera, such as many bombycine moths, and they even appear to a slight extent in certain caddis-flies. The authors mentioned, especially Mayer, whom we quote, claim that “dull ochre-yellows and drabs are, phylogenetically speaking, the oldest pigmental colors in the Lepidoptera; for these are the colors that are assumed by the hæmolymph upon mere exposure to the air. The more brilliant pigmental colors, such as bright yellow, reds, greens, etc., are derived by more complex chemical processes. We find that dull ochre-yellow and drabs are at the present day the prevalent colors among the less differentiated nocturnal moths. The diurnal forms of Lepidoptera have almost a monopoly of the brilliant colorations, but even in these diurnal forms one finds that dull yellow or drab colors are still quite common upon those parts of their wings that are hidden from view.”
The more primitive moths being more or less uniformly yellowish or drab, the next step was the formation of bars, stripes, finally spots, and eyed spots, these markings in the later forms appearing simultaneously in one and the same species of certain highly specialized moths and butterflies. All that has been said will prepare the reader for the consideration of the subject of insect coloration. The origin of such markings has been discussed by Weismann, Eimer, Haase, Dixey, Fischer, and others.