200 COLOR PHOTOGRAPHY. 



of Papelis wrens was situated before coming out of the cocoon upon 

 wood which lay next to brick. After shedding the skin its lower side 

 took on the color of the wood on which it lay, while the upper was of 

 the color of the brick. Poulton 1 remarks, on the other hand, that a dif- 

 ference between the color of the back and of the abdomen is frequently 

 to be observed in pupse. Yet this may perhaps be attributed to the 

 fact that these surfaces are usually subjected to different illumination. 



The experiments of Poulton led, however, to a contrary conclusion. 

 He arranged so that the front and rear portions of a caterpillar should 

 be differently illuminated, an experiment which he designates as the 

 "conflicting color experiment." 2 No local coloring was distinguished, 

 but a uniform average color over the whole body, which depended on 

 the relative surfaces of the two parts, and without a preponderating 

 influence being exerted by the front part. 



The experiment of Poulton by which he established the facts of states 

 of greater sensibility also speaks against the simple nature of the pro- 

 cess. These periods occur at the time of changing into pupse. In the 

 "Transference Experiments" the change of surroundings occurred 

 shortly before such changes, and in spite of this the first surroundings 

 usually appeared more influential than the second upon the coloring 

 which the caterpillar assumed after the changing into the pupa. The 

 second skin is, of course, formed beneath the first and according to 

 Poulton possesses no coloring matter. The future coloring of this skin 

 is therefore influenced before it possesses coloring matter.' 5 One must 

 agree with Poulton when he rejects for these cases the assumption 

 of a simple photographic process and supposes complicated physiolog- 

 ical causes. 4 



In spite of this I do not regard it as impossible that a relation to 

 color photography exists in so far that the coloriug matter of caterpillars 

 possesses the characteristics of a color-receptive substance to a certain 

 degree. Naturally Poulton could not assume such a relation, for the 

 basis of color photography was not then determined. There was for 

 him, therefore, a break in the understanding of the color adaptation of 

 caterpillars, which he expresses as follows : 



"Some quality in the light reflected from surrounding objects forms 

 the cause, but the physiological chain which connects the two [color of 

 illumination and of the skin] has yet to be discovered." 



1 Poulton. Phil. Trans., 178: page 315. 1887. 



2 See, for example, Phil. Trans., 178: page 373. 1887; Colors of Animals, page 131; 

 Trans. Ent. Soc., pages 420, 446. 1892. 



"I have to thank the kindness of the lepidopterologist connected with the institu- 

 tion, Mr. Omar Wackerzapp, for informing me that the caterpillars of Geometva 

 vemaria change from green in summer to hrown with the dying of the leaves, and in 

 the next spring return again to their former green color. In neither case, however, 

 is there a change of skin in connection with the color change. See Stetl. Entom. 

 Zeit., pagel, 1889. It is, however, not established that the light is here the cause of 

 the change. 



'Poulton. Phil. Trans., 178 : page 317, 1887 ; Trans. Ent. Soc, page 391. 1892. 



