LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 95 



intensities of the two plates were in a 

 ratio somewhat greater than 1 :2, the 

 fish showed differential response to- 

 ward them by a difference in frequency 

 or method of approach to them. With 

 less intensity difference no differential 

 response was observed, (p. 37.) 



17. A single sunfish, 8 cm. long, was given 

 160 trials before two white plates of 

 different intensities, and was fed be- 

 fore the duller plate. The fish dis- 

 criminated at once plates differing as 

 1 to 4. In an attempt to use the food 

 association thus established the fish 

 discriminated plates differing in in- 

 tensity as 1 :3 poorly but not those 

 that differed less. (p. 38.) 



II. Discrimination of light of different wave-lengths 

 a. White-red 



18. Fifty trials were given to each of two 

 horned dace by feeding before a white 

 plate presented at the same time with 

 a red of different intensity. These 

 fish were accustomed to red and were 

 not red-shy. After 30 trials each fish 

 made 80% to 90% of correct or white 

 choices, and each finally gave 10 suc- 

 cessive correct choices. (p. 23.) 



19. By means of a peculiar unlearned re- 

 sponse of the dace of section 18 to red 

 and white plates these plates were 

 matched in brightness for them. (p. 

 24.) 



20. Twenty trials were then given to each 

 of the horned-dace of section 18 before 

 these red and white matched plates, 

 while the fish were fed before the white. 

 Seventy per cent of correct or white 

 choices were obtained. (p. 25.) 



