DISCRIMINATION OF LIGHT BY FISH^ 



I. STATEMENT OF THE PROBLEM 



In the early part of the second half of the nineteenth 

 century many comparative studies of the anatomy of the 

 eye were made. Studies of the physiology of the human 

 eye followed, but experimental work upon animal vision 

 was delayed. Not until 1885 were Graber's results pub- 

 lished. He was among the first to test experimentally 

 the effects of light of different wave-lengths upon fish, and 

 found that they showed a preference for the shorter wave- 

 lengths. Then a number of other experimenters decided 

 that fish discriminate color. But in 1909 and 1910 Hess 

 published an account of experiments from which he con- 

 cluded that fish do not show the responses to wave-length 

 apparently established by his predecessors in this field. 

 He attributed the responses obtained by him as well as 

 those already obtained by others to differences in the 

 brightness rather than to differences in the quality of the 

 light used and held that fish are color-blind. His evidence 

 has been given favorable consideration by a number of 

 investigators of color vision in higher vertebrates (Watson 

 1914, Parsons 1915). From this discussion arose the 

 definite problem, — to determine whether fish can respond 

 to differences in wave-length of light or can respond only 

 to differences in intensity^ of light. 



II. EXPERIMENTAL WORK 



A. Introduction. — The first requirement for the solution 

 of the question was to determine whether our native fish 

 show responses' available for experimentation. For some 



1 Contribution from the Zoological Laboratory, University of Michigan 

 - In this paper intensity is used as a physical term, and brightness as a sensation 

 term; quality is used to describe that phase of sensation dependent upon wave- 

 lengths. 



^ The study of first responses will be referred to as the Method of Response. Sec- 

 tion H of this paper is devoted to the presentation of data gained by this method. 



