COLOKATION. 63 



pigment-cells, owing to the influences of light, depth of 

 water, temperature, surroundings, etc. 



In some other fishes the change of coloration is much 

 more rapid, and seems to depend on a contraction or ex- 

 pansion of the pigment-cells already developed, and which 

 are very sensitive to surrounding conditions, especially to 

 light. Owing to this rapid change in the colors of certain 

 fishes, when exposed to the light, they are thought by some 

 to be endowed with the power of changing their colors at 

 will, or voluntarily. This, however, is not very likely. 



