140 The Animal Mind 



reactions. The only structures suggesting a visual function 

 are pigment spots on the back near the head, and other pig- 

 ment cells distributed down the back. Amphioxus makes 

 negative reactions to light, especially when the light, from 

 which heat rays have been excluded by passing it through 

 water, is directed at any point on the back, the most sensitive 

 region lying just back of the eye spot (225, 311). The eye 

 spot itself, and the front end of the animal, are insensitive. 

 Fatiguing the light reactions had no effect on response to 

 other forms of stimulation (311). Attempts to test the 

 4 'color preferences" of Amphioxus by illuminating different 

 parts of a trough with differently colored lights gave negative 

 results (225). A skin sensibility to light has been observed 

 also in larval lampreys, which will give negative reactions 

 even when the optic nerves are cut (310). Blind fish have 

 been found to react to light, apparently through the skin (107). 

 Among the many animals whose supposed color prefer- 

 ences Graber tested were two species of fish, but no con- 

 vincing proof of their powers of color discrimination was 

 obtained (151). Bateson placed food on differently colored 

 tiles, and observed that the fish picked it off most readily 

 from white and pale blue, and least readily off dark red and 

 dark blue; which establishes little save that the bait was 

 probably more conspicuous on the former (12). Professor 

 Bentley and the writer succeeded in getting fairly conclusive 

 evidence that one fish, of the common variety of chub, 

 Semotilus atromaculatus, could associate a given pigment with 

 food. 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 



