The pigment may extend through the entire cuticula, but it is usually confined to the outermost layers, and occurs there in union with a peculiar modelling of the upper surface into microscopic figures which are of interest not only from their delicacy, but because they vary with each species. (See p. 184.)
The hypodermal colors, situated in the hypodermis, are, according to Hagen, the result of a chemical process, generating color out of substances contained in the body. They are easily recognized, since they fade, change, and disappear after death. But where these colors are preserved after death and enclosed in air-tight sacs, as in the elytra and scales and hairs of the body, they persist, though, as we well know, they may fade after exposure to light.
The hypodermal colors are mostly brighter and lighter than the dermal ones, being light blue or green in different shades, yellow to orange, and the numerous shades of these colors combined with white; exceptionally they are metallic, as in Cassida, and are then obliterated after death.
“The fact that such metallic colors can be retained in dead specimens by putting a drop of glycerine under the elytra, leads us to conclude that those colors are based upon fat substances. The hypodermal colors are never glossy, as far as I know; the dermal colors frequently.
“As the wings, elytra, and hairs all possess a cuticula, dermal colors are frequently to be found, together with hypodermal ones, chiefly in metallic colors. In the same place both colors may be present, or one of them alone. So we find hypodermal colors in the elytra of Lampyridæ. In the elytra of the Cicindelidæ the main metallic color is dermal, the white lines or spots are hypodermal, by which arrangement the variability in size and shape of those spots is explained.
“There occur in a number of insects external colors, that is, colors upon the cuticula, which I consider to be in fact displaced hypodermal colors: the mealy pale blue or white upon the abdomen of some Odonata, the white on many Hemiptera, the pale gray on the elytra and on the thorax of the Goliath beetle, and the yellowish powder on Lixus. Some of these colors dissolve easily by ether or melt in heat, and some of them are a kind of wax. I believe that those colors are produced in the hypodermis, and are exuded through the pore-canals.” (Hagen.)