COLOR AND COLORATION 195 



The cuticular pigments are derived, of course, from the 

 underlying hypodermis cells, and these cells themselves, more- 

 over, usually contain ( i ) colored granules or fatty drops 

 which give red, yellow, orange and sometimes white or gold 

 colors as seen through the skin; (2) diffused chlorophyll 

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

 Unlike the structural colors, which are persistent, these hypo- 

 dermal 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 Pieridse, Lycaenidae and some 

 Geometridae. 



Frequently a color pattern consists partly of cuticular and 

 partly of hypodermal colors, the hypodermal or sub-hypoder- 

 mal color forming " a groundwork upon which the pattern is 

 cut out by the cuticular color." (Tower.) Thus in Leptino- 

 tarsa decemlineata the pattern " is composed of a dark cutic- 

 ular pigment upon a yellow hypodermal background." 



Combination Colors. The splendid changeable hues of 

 Apatura, Euploca 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 un- 

 aided eye the color of the wing is either brown or violet, ac- 

 cording as the light is received respectively from the pigment 

 or from the striated surfaces of the scales. According to 

 Tower, chemico-physical colors " which are of exceedingly 

 wide occurrence, are also the most brilliant and varied of all 

 those found in insects. To this class belong all metallic, iri- 

 descent, pearly, and translucent colors, as well as blue, green, 

 and violet in almost every case." 



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 



