COLOR CHANGES AND ADAPTATION IN FISHES. 1 79 



etc., were never copied in any true sense by the fishes." But he does maintain (p. 472) 

 "that there may be very specific relations between the distribution of fight and shade 

 in the background and the pigment pattern assumed by the fish." 



Pitkin, Loeb, and others, however, appear to hold that there is in the skin of these 

 fishes an actual reproduction of the pattern in the background, especially in reference 

 to the spacial interrelationship, form, and size of the light and dark areas. On the 

 basis of this assumption very important conclusions have been formulated. 



Pitkin (191 2, p. 401) points out that since the eyes of the flatfish are so near the 

 bottom the images on the retina are much foreshortened; that is, an area on the 

 bottom having, e. g., a circular outline produces an image having an elliptical outline. 

 He maintains, however, that in reproducing the pattern of the bottom the fish makes 

 corrections for perspective distortion. He holds that the configuration of the bottom 

 is reproduced in the skin, not as it would appear to an observer with eyes in the position 

 of the eyes of the fish, but as it would appear to one with eyes directly above. Thus, 

 Pitkin ascribes to this simple vertebrate most remarkable abilities. 



Loeb (1912), overlooking entirely the question of foreshortening referred to above, 

 holds that the different points stimulated in the retina bear the same spacial interre- 

 lation as the different points in the background which produce the image; and on the 

 basis of the assumption that there is in the skin an actual reproduction of the pattern 

 found on the bottom, he maintains that the impulses, as they travel through the nerv- 

 ous system, have the same spacial interrelation as have the different points stimulated 

 in the retina. All this, he asserts, supports the theory of localization in the brain. He 

 says (p. 81): "There exists, therefore, a definite arrangement of the images of the 

 different luminous points of the ground on the retina and a similar arrangement of the 

 images of the luminous points on the skin of the fishes." And from this he concludes 

 that "vision is a kind of telephotography." 



Thus the main points of contention concern the question as to the relation between 

 the color of the environment and that of the fish, and the question as to whether or not 

 there is in the skin of the fish an actual reproduction of the pattern of the background. 



Regarding the biological significance of changes in the shade, the color, and the 

 pattern in the skin there are various opinions. Some hold that these changes are 

 purely accidental and have no biological value; others maintain that they function as a 

 protection from enemies or in capturing prey; still others assert that they are primarily 

 of value in the process of courtship and mating; a few contend that they function chiefly 

 in regulating the temperature; and some even think they are of use in all of these ways 

 and that they have still other functions. Townsend says (1909, p. 3) : "Under natural 

 conditions the changes of color are made chiefly for the purpose of concealment from 

 enemies. They are also used for the capture of prey, for signaling, warning, mimicry, 

 courtship, and other purposes." Unfortunately, however, none of these ideas are 

 supported by experimental evidence. In no case has it ever actually been proved that 

 changes in the appearance of the skin have any value whatsoever. 



In regard to the mechanism involved in the phenomenon in question, practically 

 all that is known is that it is largely dependent upon the distribution of pigment in 

 certain cells found in the skin, and that the process of distribution is to a large extent 

 regulated through the sympathetic ner\'ous system. We shall later refer directly to 

 the literature on this phase of the subject. 



