LIGHT OF DIFFERENT WAVE-LENGTHS BY FISH 87 



the two species chiefly investigated by me and that the 

 capacity of individuals of the same species is not necessarily 

 the same. Even a single individual may be expected to 

 show responses varying with age or condition. That the 

 conflicting results obtained by different investigators may 

 in some cases have arisen from difference in species used, 

 in individuals, or in ages, is possible.. It is also to be ex- 

 pected that color blindness occurs among fish as among 

 men. 



b. The responses to wave-length mediated through the 

 eyes. — The question may be raised whether the responses 

 to wave-length are conditioned through the eye. Parker 

 (1909) has shown that in the species of fish (dogfish, AIus- 

 telus canis\ eel, Anguilla chrysops; killifish, Fundulus 

 heteroelitus] scup, Stenotomus chrysops; cunner, Tauiogo- 

 labrus adspersus; tautog, Tautoga onitis; puffer, CJiilo- 

 mycteriis schoepfi; toadfish, Opsanus tan; tomcod, Micro- 

 gadus tomcod) investigated by him, the skin is not sensi- 

 tive to white light even when of great intensity. The 

 eyes remain as the only possible mediating sense organ. 

 Mast (1916) found that flounders " with both eyes removed 

 do not simulate the background either in shade, color, or 

 pattern." The evidence that with the eyes functioning 

 these fish become colored like the background upon which 

 they rest has been mentioned. AVith the sunfish there 

 never was reason to doubt that the behavior toward light 

 of different wave-lengths is governed by stimuli received 

 through the eye. The eye movements toward the source 

 of light are striking, and occur at all intensities of red light. 



c. Peculiarities of the teleostean retina. — Hess suggests 

 that fish do not necessarily have color vision because men 

 can see how it would be of use to them if present. With 

 equal reason it may be said that fish do not necessarily 

 lack color vision because men cannot see how it would 

 be of use to them if present. Yet Hess argues the lack of 

 red vision on the ground that red rays do not reach the 

 environment of certain fish. The truth is that only ex- 

 perimental evidence can determine whether color vision 

 exists in fish. This evidence has been considered and the 

 conclusion drawn that the fish used in my experiments 



