37S Papers from the Marine Biological Laboratory at Tortugas. 



COLOR DISCRIMINATION EXPERIMENTS (1905). 



I am unable to interpret the experiments of 1907, except as showing 

 color-vision in the gray snapper. The experiments of 1905 are here added 

 because, while following a somewhat different method, their results are in 

 accord with those of the later experiments. These experiments differ from 

 those of 1907 as follows : 



[a) The atherinas used were fresh, as in experiment 26 of 1907. 



(b) The preliminary feeding was therefore larger and usually included 

 300 or 400 atherinas. 



{c) The series of trials was much longer, because the fresh fish were 

 taken more readily. 



((/) Some of the atherinas sank, while the others floated. If those of 

 one color had sunk more frequently than those of the other color there 

 would have been introduced an error of position. This was not known 

 to happen except in the first 14 trials of experiment 26 above, which were 

 therefore discarded. It is unlikely that in a long series of trials fish of 

 one color sank more frequently than those of the other. 



(e) The order in which the atherinas were taken was called out bv the 

 observer and recorded by an assistant. The observer called, for instance, 

 white, white, white, blue, white, blue, blue, white, blue, blue (see under 

 trial I, table 7). The recorder gave serial numbers to the colors as called 

 and entered them opposite the name of the color in a previously prepared 

 blank. A portion of such a record representing 5 successive trials of a single 

 experiment is reproduced in table 7, which is part of an original record show- 

 ing the order in which blue and white atherinas were taken in 5 successive 

 trials in each of which 5 white and 5 blue fish were thrown. 



T.^BLE 7. 



The results of each experiment were then tabulated to show in how 

 many trials fish of each color were taken first, second, third, etc. Table 8 

 shows the result of two series of trials made on the morning of July 20, 

 1905. The table shows the same discrimination between blue and white 

 that appeared in table 3, but less marked. I have no doubt that this dif- 

 ference in results when using fresh and preserved atherinas gages accurately 

 the discrimination of the snappers in the two cases. The greater palatability 

 of the fresh atherinas results in those of the two colors being taken more in- 

 discriminately, even though the color differences are perceived. With the 

 less palatable formalin atherinas the snappers not only distinguish the colors, 

 but discriminate more sharply between familiar and unfamiliar. There is 

 this further difference between the experiments of 1905 with fresh atheri- 

 nas and those of later date with formalin atherinas. Some of the fresh 

 fish float ; others sink, and are thus brought nearer the snappers and taken 



