22 COLOR CHANGES IN ANIMALS 



may require nearly two hours. When the reverse is 

 tried and a dark fish is transferred from an illuminated 

 black-walled vessel to a white-walled one the fish 



Fig. 17. Dark phase (above) and pale phase (below) of the 

 killirlsh, Fundulus, as the results of exposure to darkand to light 

 backgrounds. Parker, Jour. Exp. Bio/., 1934, II, pi. 1, fig. I. 



blanches in a little over two minutes, though again the 

 final stage may not be reached for some four hours. 

 These changes take place in the times just given pro- 

 vided the temperature of the water in the experimental 

 vessels is approximately 20° C. At lower temperatures 

 the reaction times may be much lengthened, but under 

 all circumstances darkening appears to be accomplished 

 always more rapidly than blanching, a rule that holds 

 for the corresponding changes of a number of other ani- 

 mals (Parker, Brown, and Odiorne, 1935). It is an 

 interesting fact that when a normal Fundulus, either 

 pale or dark in tint, is put in an environment of com- 

 plete darkness it does not assume a dark tone as might 

 be expected, but it blanches strikingly and remains pale 

 (Parker and Lanchner, 1922). This fact, which has 

 been already noted in other fishes by von Frisch (191 1), 

 makes it obvious that there must be a significant differ- 

 ence in these forms between being in the dark and seeing 



