COLOR AND COLORATION 193 



>resence 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. These colors in these beetles are structural, and their variations 

 are to be attributed to slight differences in the structure of the surface. 



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 

 influences. 





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