Washburn and Bentley, Color-Discrimination. iij 



was eliminated by setting the red forceps as often on the right as 

 on the left of the green, and the second was canceled by using 

 both gates and allowing the subject to enter half the time on the 

 same side as the bait and halt the time on the opposite side. 

 Both of these c6mpensatory changes occurred in irregular sequence, 

 but an equal number of " right " and " left," of " same " and "oppo- 

 site" settings were taken at each feeding. The following sample 

 protocol for a series of experiments will serve to make this clear. 

 "Right" and "Left" refer to the position of the forceps in the 

 horizontal support; "Same" means that the fish was allowed to 

 enter compartment B on the same side as the forceps with food 

 in it, and "Opposite" means that it entered on the opposite side 

 from the baited forceps. "R" and "G" refer to the red and 

 green forceps, respectively. 



In all these experiments, numbering two hundred and twenty- 

 six exclusive of trials without bait, the red forceps held the food 

 and the green forceps w^ere empty. After August 3 mealworms 

 were used for bait instead of grasshoppers, on account of their 

 greater uniformity of appearance. In each case record was made 

 of the forceps at which the fish first bit. The accompanying 

 table (I) shows the results in the columns headed "Food." It 

 will be seen that in the first series, of fifteen experiments (food) , made 

 on July 31, the fish bit first at the red eleven times and four times 

 at the green; that in the second series of ten experiments it bit 

 eight times at the red and twice at the green, and that after this 

 point biting at the green was very infrequent; in the last seventy- 

 four experiments, from August 5 on, the green was bitten at only 

 once, on which occasion, as our notes show, the fish was ravenously 

 hungry and chancing to come straight against the green forceps 



