PROTECTIVE RESEMBLANCE, WITH EXAMPLES 71 



Hagen divided color-producing substances into dermal and 

 hypodermal, the former being located in the cuticula and the 

 latter in the cells of the hypodermis which lies under the 

 cuticula. Poulton has shown the existence of color pro- 

 ducing substances in the fat body and haemolymph, which 

 Tower designated as subhypodermal colors. Wallace states 

 that the pigmental colors have a different character in animals 

 according to their position in the integument. These epidermal 

 or cuticular colors appear in the external, chitinized skin of 

 insects, in the hairs of mammals, and partially in the feathers 

 of birds. To the hypodermal colors belong many of the reds 

 and yeUows of butterflies and birds. Tower relates that the 

 dermal colors and the substances which produce them are 

 located in the outer portion of the cuticula and are diffuse 

 pigments, which is contrary to the views of Hagen and Enteman 

 who maintained that they were present in the form of granules. 

 The hypodermal colors are usually in the form of granules 

 located in the hypodermal cells or more rarely derived pigments. 

 Many of them fade after death, while others are permanent. 



Physical or structural colors are usually produced by the 

 interference of Ught, either by reflection or by fine striae, or 

 modification in some way by the light impinging on the 

 body. These results are brought about by polished surfaces, 

 lameUse, pits, striae, scales, or other modifications. White 

 is the only physical color in insects, which is produced, 

 according to Poulton, by the enclosure of minute air bubbles 

 or transparent globules often enclosed in scales, which scatter 

 the various rays in all directions. White is also produced 

 by the flat faces of crystals and by fine granules In the fat 

 body. 



The physical color, so-called, or white, is usually combined 

 with chemical or pigmental colors, which give varied and brilliant 

 hues to insect coloration. The chemico-physical or combination 

 colors are explained by the light of one wave length being 

 neutraKzed, owing to one set of such waves being retarded or 

 shifted so as to be half a wave-length behind the other set. 

 The complementary color of that which is neutralized is seen. 

 To this class belong glossy or metallic tints in insects and in 

 birds, and also the iridescent blue, red, green, and violet hues. 



