The colors and bright markings of insects, especially those of butterflies, render them the most brilliant and beautiful creatures in existence, rivalling and even excelling the gay hues of our most splendidly colored birds. The subject has been but recently taken up and is in a somewhat crude condition, but the leading features have been roughly sketched out by the work of a few observers from a physical, chemical, and biological point of view. The colors of insects, as of all other animals, are primarily due to the action of light and air; other factors are, as Hagen observes, heat and cold, moisture and dryness, as recently shown by the experiments on butterflies by Dorfmeister, Weismann, W. H. Edwards, and later observers. They have their seat in the integument. Hagen divides colors into optical and natural. =Optical colors.=—“These,” says Hagen, “are produced by the interference of light, and are by no means rare among insects, but they are solely optical phenomena. Colors by the interference of light are produced in two different ways: either by thin superposed lamellæ, or by many very fine lines or small impressions in very close juxtaposition. “1. There must be present at least two superposed lamellæ to produce colors by interference. The naked wings of Diptera, of dragon-flies, and of certain Neuroptera often show beautiful interference colors. The wings of Chrysopa and Agrion show interference colors only for a certain time, viz., as long as the membranes of the wings are soft and not firmly glued together. Afterwards such wings become simply hyaline. “The scales of Entimus and other Curculionidæ are well known for their brilliancy, and it is interesting to remark that when dry scales are examined with the microscope, many are found partly injured, which give in different places different colors, according to the number of layers which remain. The elytra of some Chrysomelina and other beetles with iridescent colors probably belong to the same category. “2. When there are scales with many fine lines or small impressions close to each other, we have the second mode of producing colors. “The fine longitudinal and transversal lines of lepidopterous scales seem to serve admirably well to produce the brilliant effect of color-changing butterflies. But there must be something more present, as most of the scales of Lepidoptera are provided with similarly fine lines, and only comparatively few species change colors. I remark purposely that the lines in the color-changing scales are not in nearer juxtaposition.” (Hagen.)