THE COMPARATIVE PSYCHOLOGY OF COLOUR VISION 143 



Hess examined an American salamander {Diemictylus viridescens), 

 the ordinary toad {Bufo vulgaris), and the African spurred frog {Xenopus 

 Mulleri). He found that the spectrum does not appear shortened to 

 them. He also found that their range of adaptation appeared to be 

 the same as for the human eye. 



Fish. Graberi tested two species of fish, but no convincing proof 

 of their powers of colour discrimination were obtained. Bateson^ placed 

 food on coloured tiles and found that fish picked it ofE most readily from 

 white and pale blue, and least readily from dark red and dark blue, a fact 

 which can be explained by luminosity differences. Zolotnitzki^ fixed 

 dark red Cheironomus larvae and white, green, yellow, and red pieces 

 of wool of the same size and shape as the larvae to the wall of the 

 fish tank. The fish showed decided preference for the red, swam past 

 the white and green, while some of them paused at the yellow. Washburn 

 and Bentley^ investigated the chub {Semotilus atromaculatus). Two 

 dissecting forceps were used, alike except that to the legs of one were 

 fastened, with rubber bands, small sticks painted red, while to those of 

 the other similar green sticks were attached. The forceps were fastened 

 to a wooden bar projecting from a wooden screen, which divided the 

 circular tank into two compartments, and hung down into the water. 

 Food was always placed in the red pair of forceps, which were made 

 frequently to change places with the green ; and the fish was caused 

 to enter the compartment half of the time on one side, and half of 

 the time on the other. This was to prevent identification of the food 

 fork by its position or the direction in which the fish had to turn. The 

 animal quickly learned to single out the red fork as the one important 

 to its welfare, and in forty experiments, mingled with others so that the 

 association might not be weakened, where there was no food in either 

 fork, and where the forceps and rubber bands were changed so that no 

 odour of food could linger, it never failed to bite first at the red. More- 

 over, the probability that its discrimination was based upon brightness 

 was greatly lessened by using, when experimenting without food, a 

 different red much lighter than that in the food tests. The fish success- 

 fully discriminated red from blue paints in the same way, and it was 



^ Grundlinien znr Eijurschuufj des HelUgkeUs- u. Farbcn/iiimes dcr Thierc, Prag and 

 Leipzig, 1884. 



- Jl. of the Marine Bwl. Afi.soc. U. K. i. 225, 1887. 



3 Arch, de Zool. exper. ix. 1901. 



* J. of Comp. Near, and Psychol, xvr. 11.3, I'JOG ; Waslihuin, The Animal Mind, 

 New York, 1908. 



