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 
(cellular 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. 
