Spuler, however, finds that green does not depend on pigmentation, but is an optical color. As remarked by Spuler, either the chitin of the scales itself is colored reddish (yellow grayish), or the pigment is secreted in the nuclei.

A. G. Mayer believes that the pigments of the scales are derived from the hæmolymph or blood of the pupa, for the following reasons: (1) He is unable to find anything but blood within the scales during the time when the pigment is formed. (2) In Lepidoptera generally the first color to appear upon the pupal wings is a dull ochre-yellow, or drab, and this is also the color assumed by the blood when it is removed from the pupa and exposed to the air. (3) He has succeeded by artificial means in manufacturing several pigments from the blood which are similar in color to various markings upon the wing of the imago; chemical reagents have the same effect upon these manufactured pigments that they do upon the similarly colored pigments of the wings. “It should be here noted,” he says, “that in 1866 Landois pointed out the fact that the color of the dried blood of many caterpillars is similar to the ground color of the wings of the mature insect.”

Ontogenetic and phylogenetic development of colors.—The colors of the wings of Lepidoptera, as is well known, are acquired at the end of the pupal state. The order of development of the colors in the pupal wings has been observed by Schaeffer, Van Bemmelen, Urech, Haase, Dixey, Spuler, and A. G. Mayer. The immature wings are at first transparent and full of protoplasm. The transparent condition of the wings corresponds to the period before the scales are formed, and when they are full of protoplasm; they then become whitish as the scales develop; the latter are at first filled with protoplasm, and afterwards turn whitish, being little hollow sacks filled with air. After the protoplasm has completely withdrawn from the scales, the blood of the pupa enters them, and then the coloring-matter forms. (Mayer.) He adds that “about twenty-four hours after the appearance of the dull yellow suffusion the mature colors begin to show themselves. They arise, faint at first, in places near the centre of the wings, and are distinguished by the fact that they first appear upon areas between the nervures, never upon the nervures themselves. Indeed, the last place to acquire the mature coloration are the outer and costal edges of the wings, and the nervures.”

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.

LITERATURE

Heer, O. Einfluss des Alpenklimas auf die Farbe der Insecten. (Froebel u. Heer, Mitth. aus dem Gebiete der theoret. Erdkunde, 1836, i, pp. 161–170.)