MAYER: COLOR AND COLOR-PATTERXS. 175 



two causes: (1) Pigments derived from their food-plants, chloro- 

 phjdl and xanthophyll, and j^robably others ; (2) pigments proper 

 to the larvae, or larval tissues made use of because of some (merely 

 incidental) aid which they lend to the colouring, e. g. fat." Poulton 

 concludes that all green coloration is due to chlorophyll, and 

 that nearly all yellows are due to xanthophyll. All other colors, 

 including black and white and some yellows, are due to pigments 

 pi-oper to the larvae themselves. 



Later, in 1893, Poulton proved that the larvae of Tryphaena 

 pronuba could transform both etiolin and chlorophyll into a laiwal 

 coloring matter, which may be either green or brown. It thus 

 appears that some brown pigments are dtsrived from food, and are 

 merely modified plant pigments. Green larvae have green blood, 

 and this color is due to chlorophyll in solution. It is remarkable 

 that this chlorophyll solution is stable under the prolonged action of 

 light, and in this respect is different from any other known solution 

 of chlorophyll. It is worthy of note, further, that the spectrum 

 of this green blood shows a great resemblance to that of chlorophyll. 

 "In fact the two spectra are far nearer to one another than the 

 ordinary spectrum of chlorophyll in alcoholic solution, is to the 

 unaltered chlorophyll of leaves." 



(2) Pigments of Imagines. In 1891, Urech showed that the 

 similarity between the color of the urine of butterflies and the 

 principal color of their scales is so close that it cannot be considered 

 as accidental, but rather must be regarded as physiological. Urech 

 compares in a table the color of the urine and that of the scales 

 of 29 species of Lepidoptera. In all but two species the resem- 

 blance is very close. ^ 



Urech further shows that the color of the urine (and the corres- 

 ponding color of the scales) is not dependent upon the kind of food, 

 for one and the same food plant may be differently digested in 

 different groups of Lepidoptera. Thus he compares the behavior of a 

 Vanessa with that of one of the Micro lepidoptera (leaf-rollers) . Both 

 of these feed upon the nettle (Urtica). In the larva of the Vanessa the 

 contents of the stomach are intensely green, but become red in the 

 pupa. In the case of the leaf-roller the contents of the stomach are 

 never markedly green and become insipid in color during the pupal 

 stage. 



' Likewise, Hopkins ('94) has shown that in the Pieridae the urine is tinged by a yellow 

 substance having exactly the color of the wings. 



