=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.”
“To a certain extent the dermal colors may have been derived from hypodermal colors, as the cuticula is secreted by the hypodermis, and the colors may have been changed by oxidation and air-tight seclusion. The cuticula is in certain cases entirely colorless,—so in the green caterpillar of _Sphinx ocellata_; but the intensely red and black spots of the caterpillar of _Papilio machaon_ belong to the cuticula, and only the main yellow color of the body to the hypodermis.” (Leydig, Histiol., p. 114.)
“The dermal colors are red, brown, black, and all intermediate shades, and all metallic colors, blue, green, bronze, copper, silver, and gold. The dermal colors are easily to be recognized as such, because they are persistent, never becoming obliterated or changed after death.” (Hagen.)
Minot and Burgess refer to the cuticular colors of the cotton-worm (Aletia), the dark brown color belonging to the cuticula or crust. “Upon the outside of the crust is a very thin but distinct layer, which in certain parts rises up into a great number of minute, pointed spines that look like so many dots in a surface view. Each spine is pigmented diffusely, and together they produce the brown markings. The spines are clustered in little groups, one group over each underlying hypodermal cell.” (U. S. Ent. Comm., 4th Report, p. 46.) Minot also shows that in caterpillars generally a part of the coloration is caused by pigmentation of the cuticula.
In a dull-colored insect, such as the Mormon cricket (Anabrus), the coloration, as Minot states, depends principally upon the pigment of the hypodermis shining through the cuticula. “Most of the cells contain dull, reddish-brown granules, but scattered in among them are patches of cells bright green in color. I have observed no cells intermediate in color; on the contrary, the passage is abrupt, a brown or red cell lying next a green one. Indeed, I have never seen any microscopic object more bizarre than a piece of the epidermis of Anabrus spread out and viewed from the surface.” (2d Report U. S. Ent. Comm., p. 189.)
