240 PROCEEDINGS OP THE AMERICAN ACADEMY 



corresponding not iridescent scales of the under side of the wing also 

 affected, and at the same time with those of the ujiper side ? It can 

 only be supposed that the quicli effect upon the scales on one side of 

 the wing gives easier access to tlie scales on the other side. I confess 

 tliat I am not entirely satisfied with this explanation, but I do not 

 know of a more satisfactory one. For the first experiment the wings 

 were cut through the middle of the color-changing part, and were 

 therefore perhaps more quickly affected. In subsequent experiments 

 with entire wings of Euploea superba the iridescence was gone iu 

 three-quarters' of an hour, but the wing was only less dark even in the 

 color-changing part. In the same space of time wings of Apatura 

 Iris and Ilia, and of Thecla gucrcus were entirely bleached, those 

 of Lyccena Damon only partly. The question whether the striaj of 

 scales with more distant lamella3 will help to produce iridescence, 

 which the same kind of stride of scales with not distant lamellaj does 

 not do, I am unable to answer. 



The colors of butterflies change mostly from purple to blue, some- 

 times to yellow. Probably a calculation based upon the appearance 

 of these colors might help to solve the question. 



An interesting observation by Professor Graber * is here to be 

 noticed. When caterpillars of Apatura are kept in diffiised light, the 

 wings of the butterfly show almost no iridescence. The wings of 

 Vanessa polychloros have slate-colored marginal spots instead of the 

 commonly blue ones, when the caterpillars are raised under yellow 

 glass. As no authority is quoted, these observations may have been 

 made by Professor Graber himself. It is obvious that here a new 

 and interesting field for experiments is open. The record of Profes- 

 sor Graber's observations is too fragmentary to go farther with conclu- 

 sions based upon them, the more so as such isolated experiments need 

 always the support of reiterated observations before they can be 

 accepted as facts. This would be needed here even more, as it is 

 difficult to understand how a different light could work through the 

 skin of a caterpillar on the wing of the imago which is scarcely 

 beginning to be built up in the interior of the caterpillar. If true, it 

 would be an important discovery. An observation by G. Schoch f 

 does not corroborate Professor Graber's statement, at least for the 



* V. Graber, Insectcn, 1877, vol. ii. p. 38. 



\ G. Schoch: Mittheil. d. Rchwcizer cntora. Gesell. 1880, vol. v. p. 540. 

 Zucht von Eiiprcpia caja im gefiirbteni Licht. 



