ASSOCIATION AND COLOR DISCRIMINATION 447 



of the skin conform to the general background rather than to 

 some particular part. In males the reactions are more pro- 

 nounced than in females. Frisch concludes that the stimulus 

 is received through the eye, since blinded fishes show no adap- 

 tive changes. 



Sumner ('11) states that the skin of the flatfishes, Rhom- 

 boidichthys podas, PJiombas laevis, and Lophopsetta maculata, 

 shows adaptation in pattern, shade, and color. They react to 

 black, brown, and gray, but not to red and yellow. Such 

 changes take place irrespective of the intensity of illumination. 



Mast ('14) finds that the flounders, Paralichthys and Ancylop- 

 setta, simulate their background in shade, color, and pattern, 

 exhibiting a remarkable ability to mimic blue, green, yellow, 

 orange, pink, and brown backgrounds. Production of color 

 changes is regulated by stimulation through the eye and de- 

 pends upon the length of the light waves. That this indicates 

 color vision is supported by the fact that flounders adapted to 

 blue and green, when allowed a choice of backgrounds of different 

 colors, prefer the background with which they harmonize in 

 shade and color. 



In his observations on coral-reef fishes, Longley ('14, '15, '17) 

 finds that color changes in the pigmentation of the skin are cona- 

 mon among even the most brightly tinted fishes, and that the 

 colors have a tendency to resemble those of the surroundings. 



In general, these observations seem to indicate that fishes of 

 various genera exhibit adaptive reactions in their pigment cells 

 to backgrounds of various colors, that the stimulus is received 

 by the eye and transmitted through the central nervous system. 



Mating colors. Bright colors, particularly reds and yellows, 

 appear on the ventral side of the males of many species at the 

 time of spawning. The amount of light at the place of spawning 

 must be sufficient for the female to perceive the colors if they 

 have any recognition value. Frisch ('12) cites examples of 

 fishes possessing such colors and spawning in shallow water by 

 day light and also of fishes spawning in deep water or at night 

 which do not exhibit decorative coloration. 



