246 PROCEEDINGS OF THE AMERICAN ACADEMY 



colored rays will be emitted from this layer in all directions which 

 face toward the impinging ray of light, and in the repeated penetra- 

 tion of the colored layer their color will increase in intensity." 



I am not yet prepared to assert with certainty that such transparent 

 colors exist in insects. It is obvious that the different layei's of the 

 cuticula, when possessing a peculiar color, would answer exactly the 

 conditions above stated, the more so as a glossy surface is frequent 

 among insects. Perhaps some remarks by Graber (lusecten, i. p. 17) 

 belong here. " Most frequently the hypodermis is colored brown or 

 red, even in such insects as are externally entirely green, as the grass- 

 hopper, or black, as the cricket. This fact is to be explained partly by 

 the refraction of the cuticula, and partly by its peculiar color." If 

 Graber's observation proves to be true, the explanation will be suffi- 

 cient, and then we have a right to assume that similar cases may occur 

 among insects. Transparent colors would belong to the dermal colors, 

 modified perhaps by the underlying hypodermal colors. 



2. " Body colors in an artistic sense [Bezold, p. 57] differ entirely 

 in their action from transparent colors. They are likewise transparent 

 in very thin layers, and with them it is also the light that has passed 

 through the pigment which exhibits the characteristic color of the 

 latter ; but the great difference in the optical action of the pigment 

 and of the medium, makes it impossible for the light to penetrate 

 through layers of any perceptible thickness. On account of this dif- 

 ference a division in transmitted and reflected light takes place at all 

 the surfaces of separation of the particles of the coloring matter, so 

 that the portion of transmitted light is' already reduced to an almost 

 inappreciable quantity at an insignificant depth below the surfixce. 

 The same is of course true of the light sent forth by the lower sur- 

 face, and this explains why such colors are opaque when applied in 

 tolerably thick layers. The light reflected by body colors will always 

 contain a larger quantity of white light than light that is reflected by 

 transparent colors. This is the reason why that brilliancy and depth 

 or fulness can never be attained by body colors as by transparent 

 ones." 



It is therefore obvious that just this kind of color is very frequent 

 among insects, and not only in dermal, but also in hypodermal colors, 

 when the cuticula covering them is perfectly hyaline. 



3. " Surface colors [Bezold, p. Gl] are the consequence of bodies 

 which cause a division of the light falling upon them, which allow 

 rays of a specific degree of refrangibility, or, in other words, of certain 



