COLOR PHOTOGRAPHY. 197 



Wood, the discoverer, assumed as the cause of the phenomenon a 

 photographic sensitiveness of the skin, but gave no proof. His 

 assumption was not, however, completely self-evident; for there are 

 cases of quick color adaptation known which rest upon other grounds, 

 as, for example, among frogs and fishes. In these animals the color 

 adaptation is dependent on sight. If they lose the use of their eyes, 1 

 be it at the instance of the experimenter or accidentally, they lose their 

 capacity for color adaptation. This rests, however, not upon a change, 

 but only on a different arrangement of the coloring matter through the 

 shrinking together of the color-bearing cells or so-called chroniato- 

 phores ( ?), which lend to the chameleon 2 the remarkable capacity for 

 color changing. 



Upon these grounds Poulton thought it desirable to seek, first of all, 

 for a similar connection in the case of caterpillars. He covered the 

 eyes of a number of caterpillars with an opaque screen.' They did not, 

 however, lose the capacity for color adaptation. 



His attention was then directed to the hairy spines 4 of the cater- 

 pillars under investigation, to see if they perhaps might hide some 

 light-sensitive organ. But this supposition proved erroneous. The 

 shorn caterpillars retained their capacity for color adaptation. 



The skin must therefore contain these organs. Poulton 5 investigated 

 the physical constitution of the coloring in Amphidasis belutaria, the 

 birch-moth, which possesses this color receptivity to a high degree. This 

 moth owes the green color to a coloring matter contained in oil cells in 

 the fatty layer which lies between the epidermis and the surface 

 muscles. The epidermis itself may also secrete a dark coloring matter, 

 which then hides the green pigment and makes the skin appear brown. 



The different colorings are here formed, therefore, not by different 

 layers of unchangeable color substances, but through the formation of 

 new coloring matter and its alteration under the action of light. The 

 most effective changes take place in the dark cells in the epidermis, 

 but the green lying beneath is influenced. The range of colors thus 

 possible runs from brown, green, and gray on the one side to black and 

 on the other to white." 



If, now, the color adaptation of caterpillars is connected with the 

 color reproduction in body color photography, the dark coloring matter 

 must be formed in the dark and the lighter colors result from the action 

 of light uxion it. Poulton, indeed, observed that in the dark, dark- 

 colored caterpillars and pupae were formed by preference, while the 



Experiments and observations of Lister and Pouchet. See Semper, loc. cit., 

 page 117; Poulton, Colours of Animals, page 85. 



2 See Ernst Brlicke, Untersuchungen iiber den Farbenwechsel des Afrikanischen 

 Chamaleons. 1851 and 1852. Ostwald's Klassiker, 43. 



3 Poulton, Pbil. Trans., 178: pages 323, 345 ff. 1887; Colours of Animals, page 128. 



4 Poulton, Phil. Trans., 178: page 335, 1887; Colours of Animals, page 128. 



6 Poulton. Trans. Ent. Soc., page 357. 1892. 



6 Poulton. Trans. Ent. Soc., page 359. 1892' 



