COLORS OF INSECTS. I 23 



optera and in Hemiptera, Lepidoptera, and Hymenoptera. These pigments 

 are elaborated in the cells in which they are found, and have no connection 

 with the red pigments of the Malpighian tubules at pupation. In the scales of 

 Lepidoptera, Hopkins has demonstrated in the Pieridae the existence of com- 

 pounds of uric acid which produce white and yellow pigments. Griffiths fur- 

 ther isolates and studies a green pigment which is allied to uric acid, or is a 

 uric-acid derivative called lepidopteric acid (CnH^AzsNgOjo?). Urech, 

 Mayer, and others have made various experiments and tests with the pig- 

 ments in the scales of Lepidoptera, but without any definite results as far as 

 their chemical nature is concerned. Mayer has shown that the pigments in 

 the scales of some butterflies and moths are elaborated from the haemolymph, 

 possibly through the action of ferments. He has performed some interesting 

 and instructive experiments with the haemolymph of various moths, but comes 

 to no satisfactory conclusion concerning the nature of the pigments. 



The subhypodermal pigments have been most completely investigated by 

 Poulton and his pupils in Lepidoptera, and by myself in Coleoptera. It 

 appears from these researches that these pigments are largely characteristic of 

 phytophagous larvae, or of carnivorous larvae which feed upon certain phy- 

 tophagous species. Poulton has shown clearly that these pigments are derived 

 from the food or, largely, from pigments contained in the food. 



PHYSICAL OR STRUCTURAL COLORS. 



These colors are produced by some of the various physical principles 

 whereby light impinging upon a body is modified by reflection, refraction, 

 defraction, or dispersion. These results are brought about by polished sur- 

 faces, lamellae, pits, striae, scales, or other surface modifications. As far as is 

 known there is only one physical color in insects, namely, white, which is 

 produced either by air in scales, by the fiat faces of crystals, or by fine gran- 

 ules in the fat body, all of which give total reflection. 



Although colors are produced by physical causes in insects with great fre- 

 quency, they are, as shown by Mayer in Lepidoptera and by myself in other 

 orders, usually combined with chemical or pigmental colors, and it is to these 

 that insects owe their varied and brilliant hues. 



CHEMICO-PHYSICAL OR COMBINATION COLORS. 



These colors were first clearly recognized and defined by Mayer (1897) in 

 Lepidoptera. To this class belong all metallic, iridescent, and pearly colors, 

 as well as blue, green, violet, and many reds. The combination of a structural 

 and pigmental color in the same scale was early noticed by Urech, who showed 

 that in some Vanessas the scales had pigments which produced color and 

 interference colors due to striae, and he gave a similar case in certain Lycae- 

 nidae. These colors I have studied extensively, and I find them to be the 



