228 BULLETIN OP THE BUREAU OP FISHERIES. 



Adaptation in color. — The observations on adaptive simulation of colors show that 

 the reactions of the chromatophores depend upon the length of the waves of light 

 regardless of the intensity. Each wave-length, within certain limits, has a specific 

 effect. Thus the red causes extension of the pigment granules in the xanthophores 

 and the melanophores, yellow causes greater extension in the former and less in the 

 latter, etc. 



If each chromatophore is connected directly with given cells in the retina, it must 

 be assumed that the impulses which travel through a given nerve fiber from the retina 

 to the skin differ and that the character of each impulse depends upon the length of 

 the waves. Thus adaptation to monochromatic light might be explained, but colors 

 produced by mixtures of light waves of different lengths are also simulated. As a 

 matter of fact, most of the colors tested were not monochromatic. The different shades 

 of brown, e. g., which were very accurately simulated, were produced by mixing red 

 and yellow pigments. These pigments on drying aggregated in such a way as to form 

 small adjoining red and yellow areas, distinctly visible under a magnification of 50 

 diameters; the brown color, therefore, consisted of a mixture of red and yellow rays. 

 It thus becomes evident that a given reaction of a chromatophore is not necessarily 

 specifically associated with a given length of light-wave. In other words, the effect of 

 light consisting of waves of a given length is modified by the presence of light consist- 

 ing of waves of a different length, and the modification is different for every wave- 

 length. Where and how this process of modification occurs is unknown, but it seems 

 most natural to refer it to the activity of cells in the brain. 



The melanophores, as well as the xanthophores, take part in the production of 

 colors in the skin. Their reactions are consequently dependent upon the length of the 

 waves of light as well as upon the intensity, and to account for this as well as to account 

 for the response of the xanthophores it is necessary to add to the complexity of the 

 mechanism postulated to explain adaptation in shade. The nature of this addition is 

 at present quite obscure. 



Adaptation in pattern. — In the case of adaptation in pattern there is an integration 

 of the action of impulses from the two eyes similar to that considered under adaptation 

 in shade. If one eye receives stimuli from a background having a coarse pattern and 

 the other from one having a fine one, the skin assumes a pattern intermediate in 

 texture. Thus it is evident that the stimuli from either eye modify the effect of those 

 from the other eye. With reference to the action of each eye alone it was found that, 

 while the dark and light areas produced in the skin bear to those of the images in the 

 retina a definite relation in size, they bear no such relation in form or in special interrela- 

 tion. Obviously, then, the regulations of patterns can not be explained on the assump- 

 tion of a direct and specific nervous connection between the chromatophores in the skin 

 and the cells in the retina. An illuminated spot of a given size and intensity produces 

 the same effect on the chromatophores in the skin, no matter where it may be located 

 or what form, within certain limits, it may have. Different configurations (a, b, c, d, e, f , 

 etc.) in the retina, no matter where they are located, all may result in the same configura- 

 tion in the skin. Consequently, if the pattern in the skin depends upon the spacial 

 interrelation of the impulses, their interrelation must be reorganized somewhere between 

 the retina and the skin, probably in the brain. 



