204 BULLETIN OF THE BUREAU OF FISHERIES. 



the simulation of the background, so marvelously developed in these creatures, is in 

 any way influenced or affected to an appreciable extent by any direct action which the 

 stimulating agents in the environment may have on the chromatophores. Consequently 

 if we are ever to obtain an insight into the mechanism of this phenomenon of adaptation 

 it must be through a study of the chromatophores in their relation to the nervous system, 

 the eyes, and the environment. The reaction of isolated chromatophores to various 

 stimulating agents, recently so much studied, can throw but little light on the problems 

 concerning the evolution, the mechanism, and the function of the adaptive processes in 

 question. 



EXTENT OF DISTRIBUTION OF STIMULI FROM EITHER EYE. 



Sumner asserts (p. 459) that the flatfish Lophopseita, with either eye removed, 

 responds normally in reference to adaptation to the background. The results of my 

 experiments on Paralichthys with but one eye are in harmony with this contention. 

 In these experiments, which unfortunately were not very extensive and refer only to 

 changes in shade, the responses appeared to be normal both in time and degree. Similar 

 responses have been observed by other investigators in a number of different fishes. 

 There are, however, some species in which the removal of one eye greatly alters the 

 reactions in the skin. Thus while Secerov (1909) maintains that the chromatophores 

 in Ncmachilns barhatiila with but one functional eye respond normally over the entire 

 surface, and Frisch (191 1) holds that the same occurs in P hoxinus axid in Carassius, 

 Pouchet (1876) asserts that in trout, with one eye blinded, only those chromatophores 

 on the opposite side respond normally, and Frisch (1911) confirmes this assertion in 

 experiments on "Forellen" and "Cyprinoiden." Semper also maintains that the chro- 

 matophores in "Makropoden" and " Teleskopfishen " having but one eye respond 

 differently on opposite sides of the body. 



In all of the species in which adaptation to the background is normal after the 

 destruction of one eye, the shade, the pattern, and the color assumed on any given 

 background must be the result of an integration of the stimuli received individually by 

 each of the two eyes. This is clearly shown in reference to shade and pattern for 

 Paralichthys in plates xxix, xxx. 



If a Paralichthys is held with one eye on a black and the other on a white back- 

 ground the skin assumes a gray shade, much lighter than it does when both eyes are 

 over black and much darker than when both eyes are over white. Obviously, then, the 

 effect of the stimuli received by the chromatophores from one eye is modified by the effect 

 of the stimuli received from the other eye. (Fig. 45.) 



The same is true with reference to pattern. If one eye is held over a background 

 with large figures and the other eye over one with small figures, the pattern in the skin 

 becomes intermediate in texture between that produced by the effect of the large figures 

 and that produced by the effect of the small figures acting alone. (Fig. 41, 42, 43.) 

 When the specimen represented in these figures was fully adapted to the background 

 containing the large figures, the skin had relatively large white and black patches. 

 (Fig. 42.) A few minutes later it was so arranged that one eye was on this background 

 and the other was on the background with the small figures. It then could be seen 

 clearly that both the large white and the large black patches were breaking up, dark 

 spots appearing in the former and light spots in the latter. It is consequently evident 

 that a given stimulus in the process of simulation of the background does not have the 



