COLOR AND COLORATION 175 



chlorophyll (green) or xanthophyll (yellow) , taken from the food plant. 

 Unlike the structural colors, which are persistent, these hypodermal 

 colors often change after death, though less rapidly when the pigments 

 are tightly enclosed, as in scales or hairs. Though white and green are 

 structural colors as a rule, they are due to pigments in Pieridae, Lycaeni- 

 dae and some Geometridae. 



Frequently a color pattern consists partly of cuticular and partly of 

 hypodermal colors, the hypodermal or sub-hypodermal color forming "a 

 groundwork upon which the pattern is cut out by the cuticular color." 

 (Tower.) Thus in the Colorado potato beetle, Leptinotarsa decemlineata, 

 the pattern "is composed of a dark cuticular pigment upon a yellow 

 hypodermal background." 



The pigment present in the cuticula of tiger beetles is essentially all 

 in the primary cuticula. and is always either brown or black. In 

 certain areas the primary cuticula is pigmented and in certain areas 

 clear and transparent. This gives the color pattern. The secondary 

 cuticula beneath the unpigmented areas is full of pore canals and large 

 air-filled interlamellar spaces, and these give the effect of a white or 

 straw color depending upon the color of the secondary cuticula itself. 

 (Shelford.) 



Combination Colors. The splendid changeable hues of Apatura, 

 Euplcea and other tropical butterflies depend upon the fact that their 

 scales are both pigmented and striated. Under the microscope, certain 

 Apatura scales are brown by transmitted light and violet by reflected 

 light, and to the unaided eye the color of the wing is either brown or 

 violet, according as the light is received respectively from the pigment 

 or from the striated surfaces of the scales. 



Nature of Pigments. Some pigments are taken bodily from the 

 food; others are manufactured indirectly from the food, and some of 

 these are excretory products. 



The green color of many caterpillars and grasshoppers is due to 

 chlorophyll, which tinges the blood and shows through the transparent 

 integument. Mayer has found that scales of Lepidoptera contain only 

 blood while the pigment is forming; that the first color to appear upon 

 the pupal wings is a dull ochre or drab the same color that the blood 

 assumes when it is removed from the pupa and exposed to the air; also 

 that pigments like those of the wings may be manufactured artificially 

 from pupal blood. Pieridae are peculiar in the nature of their pigments, 

 as Hopkins has shown. The white pigment of this family is uric acid 

 and the reds and yellows of Pieris, Colias and Papilio are due to deriva- 



