COLOR CHANGES AND ADAPTATION IN FISHES. 21 7 



through the spinal cord and the sympathetic nervous system to the cells in the skin, where 

 they induce coordinated responses. It is also known that these responses may be 

 influenced by other stimuli, physiological states, and processes in general. Essentially 

 the same is true, with the exception of the part played by the sympathetic system, 

 regarding every other reaction that has been used as a criterion of color- vision in animals. 

 Nothing is known, in any case, as to what part, if any, the brain may play in the process. 



The principal difference between this criterion and that which involves muscular 

 activity is found in the course of transmission of the impulses from the brain to the 

 reacting organs. In the latter this transmission is accomplished through the motor 

 nerves; in the former, at least in part, through the sympathetic nerves. Whether or not 

 both sorts of reactions should be marshaled under the term " color- vision " is, at present, 

 very largely a matter of personal opinion. But whatever conclusion may be reached 

 regarding this, neither criterion throws any light on the question as to whether or not 

 animals have sensations of color similar to those in man, or of any other sort. That is, 

 the term "color-vision" must be used in a purely objective sense regardless of which of 

 these kinds of reaction is meant. 



In a study of the question concerning the selection of backgrounds, pursued after 

 the preceding pages were written, results were obtained which have a further bearing 

 on the problem of color-vision. In this study one specimen of Paralichthys and one of 

 Ancyiopsetia were confined for about six weeks in each of four boxes. These boxes 

 were painted on the inside, blue, green, yellow, and red, respectively; the red, however, 

 turned pink in the course of a few weeks. At the close of this period each individual 

 was tested as to the selection of colors on three consecutive days (Sept. 16, 17, and 18) 

 as follows : 



Boxes of the same kind as those mentioned above, and previously described in 

 the section on colored backgrounds, were divided crosswise in the center. One half 

 was covered with paint of one of the four colors mentioned and the other half with 

 paint of another color. In this way boxes were prepared to represent all possible pairs 

 of the four colors and one in addition, which was black and white. 



In making the tests each specimen was gently placed directly over and parallel 

 with the dividing line in the box. It was then released and the color toward which it 

 turned recorded. Each individual was given 20 trials (10 with the head facing in one 

 direction and 10 with it facing in the opposite direction) in each box that contained 

 the color to which the animal was adapted, and also, on the second and third days, in 

 the black and white box. Thus each individual was given a total of 60 trials in each 

 colored box and 40 trials in the black and white box. The results obtained in these 

 trials are summarized in table iv. The responses of Paralichthys and Ancyiopsetia in 

 each box were essentially the same. They have been added in the table, making a 

 total of 1 20 tests in each box, except the black and white, for the two individuals adapted 

 to a given color. 



By referring to the table it will be seen that the individuals adapted to pink turned, 

 in the red and yellow box, toward the red 50 times and toward the yellow 70 times; 

 in the red and green box, toward red 40 times and the green 80 times; in the red and 

 blue box, toward the red 5 and the blue 115 times; and in the black and white box, 

 toward the black i and the white 79 times. Thus they turned toward the color to 

 which they were adapted fewer times than toward any other color. 



