Color Discriininalinn i)i the Gray Snapper. 283 



The difference in the behavior of the fish toward red and blue was very 

 noticeable. They were from the first distinctly afraid of the red and took 

 them only when "they sank so that they could put the snout directly against 

 them as though smel'ling. Even then they often jerked back, as does a horse 

 under like circumstances, and did not take the fish at all, but left it to be 

 taken by another, or perhaps took it after one or two attempts. The blue 

 fish were all taken at once, and without preliminary " smelling." They w'ere 

 taken quickly. The red were taken slowly, the snappers often running a 

 little distance with them as though gingerly tasting and then finally swallow- 

 ing them. 



Such hesitation as the snappers showed in taking the red fish in this 

 experiment is to be expected even toward normal fish at the close of any 

 experiment involving liberal feeding. The evidence of discrimination lies 

 in the very much greater hesitation shown toward the red fish than toward 

 the blue at the beginning of series III. The hesitation itself is merely the 

 normal behavior of a satiated fish toward any new object in the environment, 

 but the degree of hesitation is significant. 



Since it is possible that the snappers discriminated between the red, 

 white, and blue atherinas by reason of a difference in their luminosity or 

 brightness and without distinguishing the colors themselves, it became neces- 

 sary to determine the relative brightness of the colors employed. The fol- 

 lowing tests were made : 



(i) The red, white, and blue fish were looked at against a black back- 

 ground in a light so feeble that colors could not be distinguished. Their 

 brightness diminished in the order white, red, blue. 



(2) Disks of cardboard were colored with the red and blue stains to 

 match the red and blue fish and the brightness of each of these disks was 

 then determined by the same person by comparing it on a color-wheel to a 

 gray produced by blending black and white in known proportions. Ninety- 

 seven degrees of white to 263 degrees of black matched the red in bright- 

 ness, while 2,7 degrees of white and 323 degrees of black matched the blue. 

 The luminosity o"f the blue compared to that of the red is therefore ex- 

 pressed by the fraction 



^7 X 60 -f- 32^ 2S43 blue . ^ 1 , , ,., 



J'-'-^- - - ' - >^ -^ = ^^-^ , or approxnuatelv 5 to 12. 

 97 X 60 + 263 6083 red ^^ 



(3) A spectroscopic examination' was made by transmitted light of the 

 dves used and also by reflected light of pieces of cardboard stained to match 

 the atherinas. For the latter purpose the apparatus of Mayer (1897) was 

 used. The red was found to include light of wave-lengths between 675f<./x 

 to 595ju.^, while the blue included in moderate illumination light of wave- 

 lengths between 590/4/^ and AS'^f-iJ-. A comparison of these wave-lengths 

 with Koenig's diagram as given by Howell (1906) shows that the red falls 

 in the most luminous part of the spectrum, while the blue falls in the least 

 luminous part. 



'I am indebted to Dean John O. Reed. Professor of Physics in the University 

 of Michigan, for calibrating the spectroscope used. 



