154 The Animal Mind 



the decorating instinct, finds that it does acquire such a 

 tendency, but that it does not learn to decorate itself with 

 colors matching its surroundings. The acquired "chromo- 

 tropism," or tendency to seek a certain color, in crabs might 

 be interpreted as merely a response to the brightness of the 

 colors, not to their color as such; that is the crabs may 

 after all be totally color-blind, seeing the colors as grays. 

 Stevens found indications that green comes nearest to 

 white light in its effect on the animals, by noting the 

 promptness and accuracy with which they faced the Hght. 



Experiments have been made on color discrimination in 

 spiders: some by the Preference Method, where the 

 spiders showed an inchnation for red when offered a choice 

 of compartments illuminated through red, green, blue, 

 and yellow glass (570) ; others by attempting to form an 

 association between paper of a certa'n color and the spider's 

 nest. This latter, containing eggs, was surrounded with 

 colored paper, and when a spider had become accustomed 

 to going in and out over the paper, another color was sub- 

 stituted, and a false nest made in another place, surrounded 

 by the original strips of paper. The spider under these 

 circumstances showed some confusion and tendency to go 

 to the false nest It is obvious that this method takes no 

 account of the possibility that the spider was reacting only 

 to the intensity of the colored rays and not to their color 

 as such (571). 



On the color sense of insects there are, first, the old ex- 

 periments of Graber by the Preference Method, whose most 

 definite result was to show that positively phototropic, 

 that is, light-seeking, insects prefer colors containing the 

 ultra-violet rays, while the negatively phototropic or hght- 

 avoiding ones prefer red, from which these rays are absent. 

 No proof that the discriminations were made on the basis 



