276 Papers from the Marine Biological Laboratory at Tortugas. 



obtained by the use of Diamond package dye, fast dark green, used in 

 accordance with the directions on the package. The brightness of the 3 

 colors was found on the color-wheel to be as follows : the blue equivalent 

 to a gray containing 79.5 per cent black : the light green to a gray con- 

 taining 51 per cent black ; the dark green to a gray containing "9 per cent black. 

 After the snappers had been fed on blue atherinas for about 10 min- 

 utes 2 trials were made with the blue and light green, followed by one with 

 the blue and dark green. The results are given in table 5, which shows the 

 total number of blue and green atherinas taken in each order by a colony 

 of 100 gray snappers at the east lighthouse dock, July 24, 1907. The experi- 

 ment included a blue-light-green series of two trials, and a single blue-dark- 

 green trial, each trial of 10 fish 5 blue, 5 green. 



Table 5. 



Order or place. 



Blue I 



Light green' o 



Blue 



Dark green. 



II. 



III. IV. V 



Total first 

 S orders. 



5 

 5 

 3 

 2 



Total second ! 

 5 orders. 



Grand total. 



1}' 



30 



Table 5 gives no evidence of a discrimination between the blue and 

 green colors used. These colors were, however, impure, the green includ- 

 ing some blue and the blue including some green. To my own eye they 

 were widely different, but other members of the Tortugas staff found diffi- 

 culty in distinguishing between the blue and dark-green fish as they floated 

 over the snappers. It is quite possible that the snappers would discriminate 

 between a spectral blue and a spectral green if it were possible to experiment 

 with these colors by this method. The blue-green trials are, however, of 

 interest as showing lack of discrimination on the basis of brightness, for 

 here the blue and dark green are of the same brightness, while the light- 

 green is much brighter, and yet there is no evidence of discrimination. 



Immediately after the trial of blue and dark green recorded in table 5 

 a single trial was made of red and blue floating atherinas. These 10 fish 

 were taken in the following order: R, B, B, B, B, B; 4 red fish remained 

 untaken. The record, as well as the diff'erence in the behavior of the snappers 

 toward the two colors, shows clearly that they discriminate between them. 



Experiment 2g: Blue and yellozv color discrimination. On July 26 

 snappers in all three colonies took blue formalin atherinas so slowly at 7 

 a. m. that discrimination experiments could not be undertaken. At 11 a. m. 

 the snappers at the Laboratory dock were found to take both floating and 

 sinking blue fish with some interest. After feeding them on blue for about 



