160 The Animal Mind 



different parts of a trough with differently colored lights 

 gave negative results (406). Hess (306) found that the 

 maximal effect on the activity of Amphioxus was exerted 

 by the yellow and green rays, the red and violet being much 

 less effective; hence he concluded that as in all inverte- 

 brates, so in this rudimentary vertebrate, total color-blind- 

 ness exists. 



True skin sensitiveness to light has been observed in 

 larval lampreys, which will give negative reactions even 

 when the optic nerves are cut (540), and in cave-dwelling 

 blind fish (201). Parker, however, finds no other fish in 

 which it exists, although it is quite common in amphibians. 

 He therefore reaches the conclusion that in vertebrates, 

 skin sensitiveness is not a primitive form of visual sensi- 

 bility, from which vision by the eye has been derived, but 

 a "secondarily acquired peculiarity." He points out that 

 the fish and amphibians which show it are freshwater 

 animals, whereas the primitive vertebrates were certainly 

 marine (545). 



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 (267). Bateson (25) 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 white and 

 pale blue. Professor Bentley and the writer (757) got good 

 evidence that the common brook chub could distinguish 

 between red and green paints, by training it to bite at for- 

 ceps to which red sticks were attached, and to refrain from 

 biting at similar forceps carrying green sticks. The pos- 

 sibility of guidance by smell or by the position of the for- 



