202 COLOR PHOTOGRAPHY. 



of the skiii lying in the dark are then places for the development of 

 dark pigment, which is of use to the whole body. That this develop- 

 ment is more rapid than in complete darkness and also more rapid for 

 caterpillars which were first in light and then in darkness than for 

 those always remaining in darkness, 1 is, perhaps, due to the action of 

 the extreme violet and ultraviolet rays of the daylight. I shall later 

 refer to a similar phenomenon in color photography. 



Further cases of color adaptation Lave been above mentioned in 

 which the eye receives the active impulse. According to Eimer 2 these 

 cases are due to the possession by the caterpillars of a long nerve train 

 extending between the place of reception of the stimulus and the place 

 of its action, the place of reception of the stimulus being restricted to 

 the eye. Semper 3 explains the color adaptation in these cases by the 

 difference in intensity of action of certain colors and of brightness of 

 the surroundings on the retina. These create, according to the obser- 

 vations of Dewar, 4 electrical currents of different strength, and thus 

 one must attribute to them different capacity for attracting together of 

 the chromatophores. With increasing strength of attraction the skin 

 appears brighter. This explanation, it will be observed, is similar to 

 that given for the caterpillars. 



Semper 5 describes a remarkable observation, according to which 

 "white rabbits breed most easily and surely in white reflected light." 

 I scarcely believe, however, that this circumstance has to do with the 

 subject under consideration. Their relatives in the far north are at 

 least, with some rea.son, ,; supposed to put on their white winter gar- 

 ment through the influence of the cold. And if each rabbit received 

 only reflected and not direct sunlight, they probably had their resi- 

 dence in a cool place. 



1 do not know whether the above-mentioned kind of color adaptation 

 has an extensive application. Perhaps, however, further examples of it 

 will be recognized when the attention of biologists is drawn to it. 7 



It is remarkable that in the strong light of the equatorial regions 

 more dark than light forms have developed. Here also a connection 

 with the light has been assumed. Thus Darwin 8 contrasts the dark 

 coloring of many birds which inhabit the southern part of the United 

 States of America with those of the north, and adds : " This appears to 



1 Trans. Eut. Soc, page 419, 1893. 



2 Eimer. Entstehung der Arten, page 156. 



3 >Seniper, loc. cit., page 119. 



1 Dewar. Nature 15, pages 433, 453, 1877. 



r \Semper, loc. cit., page 265. 



6 See Ponlton. Colours of Animals, page 94 ff., 1890; Beddard, Animal coloration, 

 page 76, 1895. 



7 I found later in Vogcl's Handbuch der Photographic, 1: 4 Aufl., 1890, pages 57, 

 203, the remarkable observation of Herschel (Phil. Trans., page 189, 1842) that cer- 

 tain vegetable coloring matters are most strongly bleached by the colors complemen- 

 tary to them. It would be interesting to observe whether in living plants, for 

 example, certain flowers had the capacity to assume the color of their illumination, 



"Darwin. Abstammung des Meuschen; German by V. Cams, 5 Aufl., page 253. 



