200 BULLETIN OF THE BUREAU OF FISHERIES. 



witz (191 3) refers to these cells or groups of cells as melanophores, xanthophores, 

 erythrophores, and guanophores, respectively. The pigment granules in these cells 

 are sometimes found massed together in a small space and at others spread out over a 

 considerable area. The color, the shade, and the pattern in the skin depend mainly 

 upon the relative position of these granules and the guanin crystals." Changes in 

 these features consequently depend upon their movements. Some maintain that the 

 cells are ameboid and that the movement of the granules is caused by changes in the state 

 of ameboid processes; others maintain that they are fixed in form and that the granules 

 move through the protoplasm or through fixed canals in it. Hooker (191 4) has recently 

 reviewed the literature on this subject. It will, therefore, not be necessary to go into 

 details regarding this matter. I shall, moreover, treat this whole matter in a subse- 

 quent paper. 



EYES, NERVOUS SYSTEM, AND DIRECT ACTION OF STIMULATING AGENTS AS FACTORS IN 



ADAPTATION TO BACKGROUNDS. 



Ballowitz (1893) and others have shown that the chromatophores are surrounded by 

 a dense network of nerve fibers ; and the results of operations on the eyes and the nerves 

 by Pouchet (1876), Secerov (1909, 1913), Frisch (191 2), Sumner (191 1), and others indi- 

 cate that these fibers are part of the sympathetic system and that the adaptive move- 

 ments of the pigment granules are largely, if not entirely, controlled by stimuli received 

 through the eyes. It has been found by these investigators and others that if the eyes 

 are destroyed, or if the optic nerves or the sympathetic trunks are cut, adaptive changes 

 in the chromatophores of the skin cease. 



The results which we obtained by means of operations on the eyes in flounders 

 confirm these conclusions in so far as they refer to the function of the eyes. In Para- 

 lichthys, it was found that the removal of either eye alone interferes only temporarily 

 with adaptive processes in the skin, but that such processes cease permanently after the 

 removal of both eyes, although blind specimens learn to move about in aquaria without 

 any apparent difficulty, and in some instances they even learn to capture minnows. 

 One such specimen was kept for over three weeks. At the end of this time the wounds 

 had healed, the eye sockets had become pigmented, and the fish appeared to be in 

 perfect condition. Changes in the background, however, had no apparent eflfect on the 

 appearance of the skin. 



There is always some degree of uncertainty as to the cause of negative results 

 after operations. Regarding some of the experiments mentioned above, Sumner 

 (p. 473) and others have raised the question as to whether the effect of the operations 

 on the chromatophores was due to the elimination of the action of the sympathetic 

 system and the eyes, in accord with the conclusions stated above, or to the injury in- 

 volved in the operation. Moreover, Spaeth (191 3), Secerov (191 3), and others maintain 

 that light, temperature, chemicals, and other agents affect the movement of pigment 

 in the chromatophores directly. They found that the chromatophores in small pieces 

 of skin separated from the body still respond to these agents. Thus the question arises 



•I Frisch C1913) maintains that in addition to the pigment granules there is in some forms a blue-green substance probably in 

 solution. He says (p. 156) that in Crenilabrus, after having been on a blue background for two weeks, pigment in the chromato- 

 phores was much condensed thus exposing the blue-grecn substance, and he also maintains that the flesh in these individuals had 

 a distinct blue-green cast not foimd in others. This, he holds, indicates that the blue-green substance increases when the fish is 

 on a blue backgrotmd. 



