COLOR AND COLORATION 177 



orange to yellow, especially as the result of exposure to sunlight. Yellow 

 in place of red, then, may be attributed to an arrested development of 

 pigment in the living insect and to a process of reduction in the dead 

 insect, metabolism having ceased. 



Yellow and green are similarly related. The stripes of Pcecilocapsus 

 lineatus are yellow before they become green, and after death fade back 

 to yellow. As the green pigment in most, if not all, phytophagous in- 

 sects is chlorophyll, these color changes are probably similar to those 

 that occur in leaves. Leaves grown in darkness are yellow, from the 

 presence of etiolin, and do not turn green until they are exposed to sun- 

 light (or electric light), without which chlorophyll does not develop; 

 and as metabolism ceases, chlorophyll disintegrates, as in autumn, 

 leaving its yellow constituent, xanthophyll, which is very likely the 

 same substance as etiolin. 



Cicindela sexguttata and Calosoma scrutator are often blue in place of 

 green. Here, however, these colors are structural, and their variations 

 are to be attributed to slight differences in the spacing of the surface 

 elevations or depressions. 



Green grasshoppers occasionally become pink toward the close of 

 summer. No explanation has been offered for this phenomenon, though 

 it may be remarked that when grasshoppers are killed in hot water the 

 normal green pigment turns to pink. 



These changes of color are apparently of no use to the insect, being 

 merely incidental effects of light, temperature or other inorganic in- 

 fluences. 



