Chromatic Function. 421 



changed to green pupee, but each corresponded exactly in tint to the 

 leaves around it, the one being dark, the other a pale, faded green. 

 Another attached itself to the wood, and the pupa became of the same 

 yellowish color ; while one fixed itself just where the wood and brick 

 joined, and became one side red, the other side yellow. " " It is a kind 

 of natural photography, the particular colored rays to which the fresh 

 pupa is exposed in its soft, semi-transparent condition effecting such a 

 chemical change in the organic juices as to produce the same tint in the 

 hardened skin." The range of colors, however, which can thus be im- 

 itated, is limited to those which usually occur in nature, in the environ- 

 ment of the animal ; a limit doubtless fixed by inherited habit. Thus 

 they do not become scarlet in any case. ( A. R. Wallace. ) 



We thus have examples of color marking by direct action of the color 

 without the intervention of a sense organ. But in those more complete 

 organisms in which a color sense becomes developed, that sense proves 

 to be the most available path of access to the organism for the stimuli 

 of the various colors ; the color sense being taken from the general tis- 

 sues and concentrated in a special organ. As long as the light rays act 

 directly on the undifferentiated eyeless protoplasm, we can understand 

 that many colors and shades might be developed in it, in an indefinite 

 and undetermined quantity. But when the influence of the light is 

 confined to one avenue, the nature and capacity of which can be 

 learned, and is necessarily a definite quantity, we can understand that 

 this influence is now measured and bounded by the degree of differen- 

 tiation of the organ. We might therefore presume that those animals 

 which are marked through the e3^es, would not be highly colored unless 

 the eye were a good one for distinguishing color. Accordingly, we find 

 that birds are more nighty colored than other vertebrates, and they have 

 the finest color sense. Among the mammals the monkey tribes, next to 

 man, have the best color sense, and many of them are adorned with 

 brilliant red, yellow, green and blue sexual colors, whereby they are 

 more conspicuous or attractive. Nocturnal animals are rarely colored. 



Any special distribution of pigments in the organic system, may be- 

 come so constant in its repetitions as to become hereditary, like other 

 habits of organic action. Accordingly, we know that colors of the skin 

 and appendages are largely hereditary as in birds, the tiger, zebra, 

 and many other mammals. It has been observed that certain pigment 

 cells that appear in the cutis of the embryo chick about the fifteenth 

 day, disappear again by the twenty-third. The embryo mammal is cov- 

 ered with colored hair, and the coloring of butterflies is developed in 

 the pupae in the dark. This proves the heredity of color habits. The 

 extent to which the coloring of animals is affected by their surround- 

 ings, is apt to escape our notice. It is a fact observed by many nat- 



