THE COLORS OF INSECTS 



203 



Natural colors. These are divided by Hagen into dermal (cuticu- 

 lar) and hypodermol. The dermal colors are due to pigment de- 

 posited 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 hypo- 

 dermal 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 be- 

 long to the cuticula, and only the main yellow color of the body to the hypo- 

 dermis." (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 pigrnented diffusely, and together they produce the brown 

 markings. The spines are clustered in little groups, one group over each under- 

 lying hypodermal cell." (U. S. Ent. Comm., 4th Report, p. 40.) Minot also 

 shows that in caterpillars generally a part of the coloration is caused by pig- 

 mentation of the cuticula. 



In a dull-colored insect, such as the Mormon cricket (Anabrus), the colora- 

 tion, 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.) 



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 fig- 

 ures 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 



