THE FUNCTION OF CONSCIOUSNESS. 499 



That sense-perceptions are stimuli to the immediate 

 appearance of structural changes or movements is ad- 

 mitted. This is shown by the production of color 

 changes in animals through changes in the condition 

 of the organs of sight. Pouchet showed that the extir- 

 pation of both eyes of the turbot, and of a Gobius, 

 paralyzed the chromatophorous cells, so that the usual 

 color-adaptations to the color of the surface of the bot- 

 tom on which they rested, could not be made. He also 

 produced the same effect on one side of a trout by re- 

 moving the eye of the opposite side. The chromato- 

 phorsB were permanently expanded, and the colors dark. 



Some experiments which I tried with tree frogs of 

 the species Hyla gratiosa, and Hyla carolinensis, are as 

 follows : The color is usually green in both species, 

 but it changes to dark brown where the frog rests on a 

 brown surface, as of bark, etc. It appears that the 

 maintenance of the brown color requires a more vigor- 

 ous nervous stimulus than the green. The frogs are 

 green at death ; and limbs which I ligated remained 

 green when the remainder of the surface became 

 brown. Now in individuals with extirpated eyes, the 

 color was always green, no matter what the surface on 

 which they rested. The power of assuming the brown 

 color was lost. 



In these experiments it is difficult to connect the 

 expansion of the chromatophorous cells as any effect 

 of consciousness of color, by direct proof. If, how- 

 ever, muscular cells can be contracted under the in- 

 fluence of mental states, a similar mechanism may be 

 supposed to exist in the case of chromatophorae. The 

 fact that the process may be now reflex does not ex- 

 clude the other fact of the influence of consciousness 



