206 TEXT-BOOK OF ENTOMOLOGY 



violet just as we find them to act towards the substance which Mr. Sorby calls 

 aphidilutein. 



"5. Mr. Sorby's four stages of the changes effected by the oxidation of 

 aphideine produce four different substances." 



Chemical and physical nature of the pigment. Researches in this 

 difficult field of inquiry have been made by Landois (1864), Sorby 

 (1871), Meldola (1871), by Krukenberg (1884), and more recently 

 by Coste, Urech, Hopkins, and Mayer, and the subject is of funda- 

 mental importance in dealing with mimicry and protective colora- 

 tion, the primary causes of which appear to be due to the action of 

 physical and chemical agents. 



Over twenty years ago Meldola observed that the yellow pigment 

 of the sulphur-yellow butterfly (Gonopteryx rhamni) was soluble in 

 water, and showed that its aqueous solution had an acid reaction. 



Besides the yellow uranidin found by Krukenberg in different beetles and 

 lepidopterous pup?e, still other coloring-matters, which are very constant in dif- 

 ferent species are readily recognized by the spectroscope. "Thus there appear 

 in the brownish yellow lymph of Attacks pernyi, CaUosamia promethea and 

 Telea polyphemus, after saponification of the precipitated soap readily effected 

 by ether, or incompletely or not removed by benzine, a chlorophane-like lipo- 

 chrome ; and in the yellowish green lymph of Saturnia pyri and of Platysamia 

 cevropia besides this pigment still another whose spectrum shows a broad band 

 on D, but which disappears with the addition of acetic acid or ammonia, as also 

 after a long heating of the lymph up to 66 C." 



Coste, and more especially Urech, have shown that many of the 

 pigments may be dissolved out of the scales by means of chemical 

 reagents, giving colored solutions, and leaving the scales white or 

 colorless. They have also shown that some of these pigments may 

 be changed in color by the action of reagents, and then restored to 

 their original color by other reagents. They have proved that reds, 

 yellows, browns, and blacks are always due to pigments, and in a 

 few cases greens, blues, violets, purples, and whites, and not, as is 

 usually the case, to structural conditions, such as striae on the scales 

 (Mayer). They confined themselves solely to the chemical side of 

 the problem, not considering the structure of the scales themselves. 



Urech has also discovered a beautiful smaragd-green coloring- 

 matter in the wings (not in the scales) of the pupa of Picric 

 brassiccK. It is not chlorophyll, and Urech suggests that it may be 

 either the germinal substance of the pigments of the scales or its 

 bearer. It is not the pigment of the blood. 



Urech has also demonstrated that in many Lepidoptera the color 

 of the urine which is voided upon emergence from the chrysalis is 

 similar to the principal color of the scales. 



