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MAYER: COLOR AND COLOR-PATTERNS. 175 
two causes: (1) Pigments derived from their food-plants, chloro- 
phyll and. xanthophyll, and probably 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 
proper to the larvae themselves. 
Later, in 1893, Poulton proved that the larvae of Tryphaena 
pronuba could transform both etiolin and chlorophyll into a larval 
coloring matter, which may be either green or brown. It thus 
appears that some brown pigments are derived 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 ofa 
Vanessa with that of one of the Microlepidoptera (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 ease 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. 
