OF ARTS AND SCIENCES. 241 



changing of colors. Enprepia caja was raised by him in different 

 colored light. The caterpillars were kept in three boxes, covered 

 with red, violet, and blue glass. Those under violet glass were more 

 voraeious than the others, and consumed twice as much food. Their 

 cry^alis transformed in the imago a fortnight earlier than the others. 

 ]Jut the images of all did not show any perceptible difference. Per- 

 haps raising of th(^ caterpillars in diffused or homogeneous light may 

 have a different effect, at least for iridescent butterflies. The Newton 

 color rings viewed with homogeneous (yellow) liglit change the coloi- 

 ' of the rings, the dimensions of which grow smaller and smaller between 

 the red and violet rings, in a proportion from fourteen to nine. I do 

 not know that iridescent butterflies have been examined under homo- 

 geneous light; perhaj^s such experiments would allow further conclu- 

 sions. 



Krukenberg * presumes the golden-green color of Carahiis auratus 

 to be an interference color. It is not changed by the influence of 

 light, nor was he able to extract from the elytra any green pigment 

 with ether, benzol, carbon of sulphur, chloroform, alcohol, even after 

 having submitted the elytra before to the influence of muriatic acid or 

 ammonia. Chlorophyll is not present, whether free or combined with 

 an acid. The chlorophyll found by K. B. Hofmann (Lehrbuch der 

 Zoocheraie, 1875, No. 3, p. 3G8) in the elytra of Cantharis is not 

 present in them, but is derived from the contents of the alimentary 

 canal. The change of the color in Cantharis is probably the conse- 

 quence of an alteration of the chitinous external integuments by cold 

 weather or by a more elevated habitation. 



Interference colors are also produced by very small impressions in 

 juxtaposition. Such an arrangement is found on the feathers of birds ; 

 for instance, on the necks of pigeons and elsewhere. In the hairs of 

 Aphrodite and Eunice this arrangement may be compared with striae 

 (Leydig). Perhaps this kind of interference colors is found more fre- 

 quently among insects than is commonly known. At least there are 

 often parts of insects, and their limbs in appearance yellowish, but in 

 a certain direction changing to brown or blackish. I know of no other 

 explanation of this not uncommon fact on the legs of Diptera, of 

 Hymenoptera, and of PhryganidiTi. G. Pouchet (Des Changements dc 

 Coloration sous I'lnfluence des Nerfs, Journ. de I'Anat. ct Physiol., 



* C. Fr. W. Krukenberfj: Vergl. physiolog. Studien an den Kiisten d. 

 Adria, 1880, 1881, vol. iii. p. G2. 



VOL. XVII. (n. S. IX.) 16 



