Color Discrimination in the Gray Snapper. 271 



ment 26) were condiicled with these preserved fish. After the formalin had 

 been as far as possible removed from them by soaking them in fresh water 

 they were dyed and used precisely as though they had been fresh. The 

 snappers took the formalin fish at first grcedilw but after a little experience 

 their rate of taking them became gradually much slower than with fresh 

 fish. This rendered it possible to make a more accurate record of observa- 

 tions, while at the same time it greatly reduced the number of atherinas 

 necessary for the preliminary feeding. 



In all the e.xperiments of 1907 the record was made by means of the 

 following device : Two blocks of wood, each 8 inches long, 2 inches wide, and 

 I inch thick are held with their broader faces together by a metal pin at each 

 end. This pin is firmly fixed in the lower block, but is received into a hole 

 bored in the upper block, so that the blocks may be readily separated. Through 

 the upper block are bored two parallel rows of holes, 10 in each row, and 

 these holes are continued for about 0.125 inch into the lower block. Into each 

 hole is loosely fitted a flat-headed copper nail an inch and a half long, 

 which is filed round and brought to a blunt, conical point. The observer 

 places one end of a sheet of commercial note paper between the blocks, so 

 that the points of the nails rest on its upper surface. If he is observing the 

 order in which red and blue fish are being taken in a trial of 10 fish, the 

 upper row of nails (nearer the end of the paper) may represent the red, 

 and the lower row the blue. The device is operated by touch, so that the 

 experimenter may watch the experiment while making the record. Begin- 

 ning at the left, he perforates the paper by pushing down a nail in the 

 upper row when a red fish is taken, a nail in the lower row when a blue fish 

 is taken. After pushing down any nail he shifts his hand one nail to the 

 right. When a record of one trial has been made, those of several suc- 

 ceeding trials are made on the same sheet by separating the blocks and shift- 

 ing the paper. If the records of successive trials are kept in alignment 

 vertically the vertical columns may be footed for each order and each color. 

 A reduced transcript of such a sheet is given in figure i, which show's a series 

 of 4 trials with light red and blue. The record of each trial is to be read 

 from left to right. In the first trial the first fish to be taken was red, the 

 next 5 were blue, and the last 4 red. The totals at the bottom of the sheet 

 show in how many of the 4 trials red and blue fish were first taken, second 

 taken, etc. The numbers are the footings of the vertical columns for each 

 color. Thus in 3 of the 4 trials blue fish were taken in the first order or 

 place and in the other red was taken in first order or place. On the other 

 hand, red was taken in the last place in all 4 trials. 



Experiment 26: Blue and white color discrimination. The fresh ather- 

 inas were divided into two equal lots. One of these was placed for 20 

 minutes in a saturated solution of methylene-blue in 0.4 per cent glacial 

 acetic acid : the other lot was placed for an equal time in 0.4 per cent solution 



