COLOR AND PATTiJLN IX ANIMALS 403 



tlicin and looking over some of the evidonco adduced for ilieir 

 support, as well as some of the criticism leveled at them, we 

 may advisedl}' look to the actual physical causation of color 

 in animals. Whatever the use or si<^nificance of color, our 

 understanding of this use must be based on a knowledge of the 

 method or modes of its actual production. 



Color in organisms is produced as color in inorganic nature 

 is. Certain substances have the capacity of selective absorj)- 

 tion of light rays, so that when white light falls on them, 

 certain colors (light waves of certain length) are al)sorbcd. while 

 certain others (light waves of certain other lengths) are re- 

 flected. An object is red because the substance of which it is 

 (superficially) composed, reflects the rvd 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 -surface may be com])osed of superposed 

 lamelke, or it may be 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 de])ths) tliat complex interference effects are 

 l):'o:laced, resulting in the practical extinguishing of certain 

 colo;s (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 observa- 

 tion, 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 i)hysical make-up. 

 As a matter of fact we shall find that most animal 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 certain others, we 

 may call, in our discussion of color jiroduction, "pigments"; 

 and "pigmental" may be used as practically synonymous with 

 "chemical" in referring to colors thus produced, while "struc- 

 tural" may be used as synonymous with "i)hysicar' in 

 referring to colors dependent on superficial structural character 

 of the insect body. For colors produced by the co(')peration 

 of both pigment and structure, "combination" or " chemico- 

 physical" may be used as a defining name.) 



Now in all animals, color depends on the presence and ar- 



