446 GERTRUDE MAREAN WHITE 



receptors on the skin. Tschermak ('15) gives a good survey of 

 vision in fishes, in which he discusses conditions of vision in 

 water, the absorption of hght by water, the formation of an im- 

 age in the fish eye, accommodation, and bifocal vision. 



LITERATURE ON COLOR VISION IN FISHES 



The question of color perception in fishes has been a matter 

 of considerable dispute and evidence concerning it has been 

 accumulated from various sources. 



Adaptatioji to background by the pigrnent cells of the skiri. The 

 expansion and contraction of pigment cells in such a way as to 

 conform the color and pattern of the skin to the background 

 against which the animal rests have been observed in many 

 fishes. If such changes in the pigment cells are brought about 

 by stimulation received through the eyes and central nervous 

 system, they may serve as evidence of color vision. Lowe ('17) 

 states that the cells of the brook-trout begin to react to back- 

 ground after the yolk-sac is absorbed. When the trout are 

 placed in a dark dish, the pigment cells expand, making the fishes 

 appear dark; but when the fishes are in a light dish, the cells are 

 contracted, giving the skin a pale appearance. 



Frisch ('12, '14) finds that Crenilabrus roissali changes in 

 color when subjected to red, green, and blue light. Adaptation 

 to green and blue light is by means of the contraction of the 

 pigment cells and also by an increase of the blue-green coloring 

 matter. He argues that the adaptation is to color rather than 

 to luminosity, for if the colors used are arranged as they would 

 appear according to their intensity to a color-blind person — 

 yellow, green, blue, red — the fish is reacting to the brightest by con- 

 traction and to the darkest by expansion. This is contrary to 

 all other experiments on the reaction of pigment cells. Frisch 

 also finds that Phoxinus laevis adapts itself to green, blue, and 

 violet by the contraction of its pigment cells which produces a 

 lighter color, and to red and yellow by expansion of the red and 

 yellow pigment cells; the color patterns remaining unchanged 

 for months under constant stimulation. The color markings 



