88 CORA D. REEVES 



and probably those used by others have color vision, but 

 certain peculiarities of the eyes of fish make it probable 

 that their color vision differs from that of terrestrial forms. 

 The fish eye shows peculiarities of the visual purple and 

 of the cones which suggest that the longer wave-lengths 

 of light may have more marked effect upon them than 

 upon man. These peculiarities are as follows: 



(1) Kottgen and Abelsdorff (1896) have published curves 

 showing the relative absorption of light of different wave- 

 lengths by the visual purple of different animals. These 

 show the maximum absorption for fish at wave-length 

 540 /A/A, while for mammals, birds, and Amphibia it is at 

 500 MAi. 



(2) According to Ewald u. Kuhne (1878) this visual pur- 

 ple in fish has not the true purple color found in terrestrial 

 vertebrates but is somewhat reddish-violet. This is sig- 

 nificant, for researches^" on organic compounds show that 

 the farther their absorption band lies toward the red, the 

 more sensitive is the chemical to light. From the differ- 

 ences in color and absorptive power between the visual 

 purple in fish and higher vertebrates, we should expect to 

 find the relative sensitivity for light of longer and shorter 

 wave-lengths different from that in terrestrial vertebrates. 

 We might even predict from the work of Kottgen and 

 Abelsdorf that fish would show the greater sensitivity to 

 red subsequently found by Bauer and others. 



(3) In another respect the retina of fish differs from 

 that of higher vertebrates. It possesses (Eigenmann and 

 Shafer 1900) large cones and peculiar twin cones, structures 



■ which may have advantages in the reception of the reduced 

 number of red rays of light. Whether wave-length dis- 

 crimination is confined to the cones (Schultze 1866 and v. 

 Kries, 1896) or is in part the function of the rods and the 

 visual purple (Kiihne 1879, Siven and Wendt 1903), the 

 fish eye has modified anatomical structures which may be 

 the basis for differences in the functioning of the eye as 

 compared with the human eye, and for increased sensi- 

 tivity to red. 



" Reported by Bayless from Luther and Nikolopoulos. 



