373 Papers from, the Marine Biological Laboratory at Tortugas. 



of acetic acid without the methylene-blue. Fresh solutions were used for 

 each experiment. The fish when taken from the solution were quickly 

 rinsed in sea-water, and all had then the same sour taste. Before beginning 

 the experiment the snappers were given a preliminary feeding of normal 

 atherinas until their rate of taking them had been reduced to between 10 

 and 20 per minute. The discrimination experiment was begun immediately 

 thereafter. 



5 light-red atherinas and 5 

 blue atherinas were thrown in each 

 trial, so that the four trials in- 

 cluded 40 fish, 20 of each color. 

 The circles at extreme right and 

 left of the sheet are perforations 

 made by the pins which hold the 

 blocks together and are not in- 

 cluded in the footings. 



Fig. I. — A reduced copy of a single record-sheet, con- 

 taining first four trials of experiment 27. 



The blue and white (or normal) atherinas were divided into lots of lo 

 (5 blue and 5 white), and these lots were thrown to the snappers in succes- 

 sion, a new lot as soon as all the fish of the preceding lot had been taken. 

 The order in which the blue and white fish were taken was recorded by 

 means of the device described above and in the form shown in fig. i. 

 Twenty-two trials were made. The records of the first 14 were discarded 

 because it was observed that the white fish sank more readily than the blue, 

 so that a position error was included. In the remaining 8 trials all the 

 atherinas were made heavier than sea-water by laying open the air-bladder 

 and emptying it by compression. All sank when thrown. These 8 trials 

 appear in table 3, which shows the total number of blue and white atherinas 



