482 ADAPTATIONS TO PHOTIC QUALITY 



Frisch were in the order yellow->green^blue->red. Since the fish reacted 

 to the 'brightest' color by contraction, to the 'darkest' color by expansion 

 of its pigment cells — this being quite unorthodox for pigment cells to do 

 — Frisch concluded that the reactions were being made to the hues per se. 



Critics were quick to point out that while these reactions admittedly 

 might be made to the hue of the background, and mediated through the 

 eyes (several investigators had been so thorough as to make sure that 

 that blinded fishes could not make them) , there was still no reason to 

 assume that the fish must therefore be consciously aware of the hues. 

 These objectors were largely silenced by the work of two American 

 investigators, Sumner and Mast. 



Sumner, in 1911, had been intrigued by the rapidity of the color 

 changes of flat-fishes as they glided over the changing bottom. In Rhom- 

 boidichthys podas, Rhombus Icevis, and Lophopsetta aquosa, he had 

 demonstrated dermal responses to shade, color, and pattern. These 

 species reacted to black, brown, and gray, but not to red or yellow. 

 A few years later Mast published his classical studies on two other 

 genera, Paralichthys and Ancyclopsetta, which in a startling way mimic 

 blue, green, yellow, orange, pink, and brown. Shade, color, and pattern 

 are all closely followed by the dermal adaptations. 



Mast painted the floors of a number of tanks, some with a single color 

 and others with two colors on the respective halves. He allowed flounders 

 to remain on single colors for six weeks, then placed each fish on the 

 dividing line of a bicolor tank floor. Blue-adapted fish swam at once to 

 the blue side of a two-color tank 88% of the time, green-adapted fish 

 70% to the green side. But red-adapted individuals turned toward the 

 red only 26% of the time. If their choice had been a 50:50 one, Mast 

 contended, it would have meant that they could not discriminate the red 

 hue from the other. 26% meant actual avoidance of red. When the other 

 side of the tank happened to be blue, red-adapted flounders went to the 

 red side only five times, to the blue 115 times! 



The responses of Mast's flounders were so immediate, so obviously 

 visual, that they were far more important than the Phoxinus work as 

 grist to the mill of the proponents of piscine hue-discrimination. But 

 brightness was not controlled, nor was a series of confusion-grays em- 

 ployed in Mast's experiments. They demonstrated color-discrimination, 

 but did they show /?Me-discrimination? By this time most of those inter- 

 ested were convinced either that Hess or Frisch was right; but some 

 remained unsatisfied with the results and the limitations of colored- 



