Color and Pattern and their Uses 587 



Tower finds, on the basis of his own researches and those of various other 

 investigators of insect colors, that among insects the chemical colors are 

 yellow, orange, red, buff, brown, black, and rarely green-blue and black; 

 physical colors are the pearly colors, almost all whites, and rarely violet- 

 greens, reds, and some metallic and iridescent colors; while chemico-physical 

 colors are violet, greens, reds, and iridescent and almost all metallic colors. 

 Tower believes it probable that but few really pure physical colors will be 

 found in insects, by far the larger part of those now classed as such falling 

 into the category of the chemico-physical. Tower finds white to be the 

 only purely physical color occurring among the Coleoptera (the insect group 

 whose colors he has specially studied). 



With regard to the situation of the pigments on which chemical and, 

 partly, physico-chem cal colors depend, these colors may be divided into 

 cuticular and hypodermal (first defined by Hagen) and subhypodermal 

 (defined by Tower). The cuticular colors are produced by coloring sub- 

 stances situated in the chitinized cuticle that overlies the whole insect body; 

 they are permanent colors, not fading after death, and are insoluble, without 

 actual dissolution of the cuticle, in water, acids, alkalies, ether, or essential 

 oils; they are browns, blackish, drab, some yellows, and possibly some reds. 

 The hypodermal colors are produced by pigments lying in the hypoderm 

 (ceilular layer of the skin, just underneath the cuticle) and are of two sub- 

 categories, viz., first some yellows and green which are due to xyanthophyll 

 and chlorophyll taken from plant-food, and which are not permanent, 

 fading after death and on exposure, and soluble in the usual organic 

 solvents; and second, certain permanent colors, reds and chrome yellows, 

 due to definite pigment granules imbedded in the cytoplasm of the hypo- 

 dermal cells. The subhypodermal colors, found practically only in larvae, 

 are due to various substances, as derived plant pigments and others, 

 in the haemolymph (blood) which show through the skin (hypoderm and 

 cuticle). 



The structural or physical colors, and the combination or physico-chemical 

 colors, to which two classes belong all white and all metallic, pearly and 

 iridescent colors, including most blues, greens, violet, and golden, depend 

 for their production on a superficial or surface structural condition of the 

 insect body or part consisting either of the superposition of one or more 

 thin transparent or translucent lamellae over a darker layer, or the fine 

 roughening of the surface by means of striae, pits, or minute hair-like processes. 

 Tower has offered a graphic classification of these colors (together with the 

 one already explained of chemical colors) in the table which follows. The 

 classification is sufficiently explained in the table to make unnecessary any 

 further discussion of the various kinds of structures involved in color pro- 

 duction among insects. 



