Color and Pattern and their Uses 
586 
Both the reasoning and the observed facts on which these hypotheses rest 
are based on the usefulness of the colors and patterns to the animals in their 
relation to the outside world. And the influence of advantage and natural 
selection is given the chief credit for determining the present-day conditions 
of these colors and patterns. 
Before, however, we take up these hypotheses, defining them and looking 
over some of the evidence adduced for their support, as well as some of the 
criticism leveled at them, we may advisedly look to the actual physical causa¬ 
tion of color in insects. Whatever the use or significance of color, our 
understanding of this use must be based on a knowledge of the method or 
modes of the actual production of color. 
Color in organisms is produced as color in inorganic Nature is. Certain 
substances have the capacity of selective absorption of light-rays so that 
when white light falls on them, certain colors (light-waves of certain length) 
are absorbed, while certain others (light-waves of certain other lengths) are 
reflected. An object is red because the substance of which it is (superficially) 
composed reflects the red rays and absorbs the others. Certain other objects 
or substances may produce color (be colored) because of their physical rather 
than their chemical constitution: their surfaces may be so composed of 
superposed lamellae, or so striated or scaled, that the various component 
rays of white light are reflected, refracted, and diffracted in such varying 
manner (at different angles and from different depths) that complex inter¬ 
ference effects are produced, resulting in the practical extinguishing of cer¬ 
tain colors (waves of certain length), or the reflection of some at angles so 
as not to fall on the eye of the observer, and so on. Such colors will change 
with changes in the angle of observation, and are the so-called metallic or 
iridescent colors. These two categories of color have been aptly called 
chemical and physical: chemical color depending on the chemical make-up 
of the body, physical on its structural or physical make-up. As a matter 
of fact we shall find that most insect colors are due to a combination of these 
two kinds. 
Substances that produce color by virtue of their capacity to absorb certain 
colors and reflect only one or more others we may call, in our discussion of 
color production, pigments, and pigmental may be used as practically synony¬ 
mous with chemical in referring to colors thus produced, while structural 
may be sometimes used as synonymous with physical in referring to colors 
dependent on superficial structural character of the insect body. For colors 
produced by the co-operation of both pigment and structure, combination 
or chemico-physical may be used as a defining name. In a recent valuable 
paper by Tower * the history of and authority for the adoption of these 
various names is given. 
* Tower, W. L. Colors and Color-patterns of Coleoptera. Decennial Pubs, of 
Univ. of Chicago, 1903, vol. X, pp. 33-70. 
