226 BULLETIN OF THE BUREAU OF FISHERIES. 



10. Changes in shade, pattern, and color result from concentration or distribution 

 of pigment granules in groups of cells known as chromatophores, in connection with 

 highl)' reflective and refractive guanin crystals found in other cells known as guanophores. 



11. The pigment granules in some of the chromatophores are black. In others 

 they are yellow, varying from yellowish green to deep orange, depending upon the color 

 of the backgroimd. 



12. The movement of the granules resulting in adaptation is under the control of 

 stimuli received through the eyes by way of the central and sympathetic nervous system. 



13. If there is any direct effect of the stimulating agents in the environment on 

 the adaptive reaction of the chromatophores it is insignificant. 



14. Stimuli received through either eye are distributed equally over the entire 

 pigmented surface. The shade, color, and pattern assumed is the result of stimuli 

 received through one eye modified by those received through the other. 



15. In Paralkhthys the shade assumed in low luminous intensity on a given back- 

 ground is practically the same as that assumed in high intensity on the same backgroimd. 

 It therefore bears no proportional relation to the amount of light received from the back- 

 ground. Ancylopsetta, however, assumes a much darker shade in very weak light than 

 it does in strong light. 



16. Light reflected from the skin to the eyes plays no part in adaptation to the back- 

 ground. Simulation of the background is not controlled b)' visual comparison of the 

 skin with the background. 



17. On a white background flounders loecome maximum white and on a gray back- 

 ground maximum gray, even if the conditions of illumination are such that much more 

 light is reflected from the latter than from the former. The action of the ligh-t received 

 by the eyes from the background must therefore be modified by light received from above, 

 but the interaction of tiie light received from the different immediate sources is probably 

 not so simple as is demanded by the ratio hypothesis of Keeble and Gamble. 



18. The simulation of the background in color is regulated by stimuli received 

 through the eyes, and it depends upon the length of the light-waves. It can not be 

 accounted for on the basis of differences in the brightness or the intensity of the light. 

 It consequently indicates that these animals have color-vision. 



19. This conclusion is, moreover, supported by the fact that flounders adapted to 

 blue or green tend to react positive!)' to these colors when simultaneously subjected to 

 stimuli from one of these and any one of the following colors: Red, green, blue, and 

 yellow, red being the darkest color and the others brighter in the order given. 



20. Flounders distinguish differences in size and in form, but the evidence obtained 

 does not indicate that their vision is acute in these respects. The fusion rate of images 

 on the retina, however, is essentially the same in flounders as it is in man, showing that 

 in respect to motions their vision is on a par with human vision. 



21. Flounders tend to select a background with which they harmonize in shade and 

 in color. 



