PKOTECTIVE COLORATION. 143 



Semper's explanation is based upon certain researches into the 

 different effects upon the eyes of different colonrs. The eye 

 is stimulated most by pure white light, and least by black, 

 the intermediate colours having an intermediate effect : thus, 

 yellow causes a stronger stimulation than violet. If, therefore, 

 the animal is surrounded by a black environment, the stimu- 

 lation of the eye will be slight, and not enough to affect the 

 chromatophores. " If the light is reflected from a red or blue 

 object, the somewhat stronger stimulation causes the black or 

 brown chromatophores to contract, wnile it does not affect the 

 red or yellow ones ; the animal then exhibits a reddish or 

 bluish tint. The light reflected from green or yellow bodies 

 produces a still stronger effect on the chromatophores, till a 

 pure white light makes all the inmost layer of the chromato- 

 phores contract, and the animal is almost colourless." The 

 chameleon * is naturally the most familiar example uf power 

 of colour change ; the physiology of this change has been 

 investigated by several naturalists, including the late Dr. 

 Krtikenberg of Jena. It appears that contractions of the 

 chromatophores can take place through stimuli, not only 

 to the eye, but to the skin ; other effects, therefore, besides 

 those of light, may produce a change of colour. f Various 

 emotions are well known to do so : if the chameleon be 

 somewhat roughly handled, it shows its anger, not only by 



* Mr. Poulton. as well as others, has remarked that the chameleon 

 becomes very dark-coloured before death ; this is not invariably the case 

 for I have had in my hands a dead chameleon of a bright hut VylUish 

 green. 



t Practically, however, a change of colour seems always due to stimu- 

 lation through the eye -and optic nerve : blinded frogs, etc., have been 

 shown to have lost the power of colour change ; and there are instances 

 on record of individual fish having been noticed whose colours did not 

 correspond to that of their fellows, and to the ground from which they 

 were taken. These individuals j;)'oi'ed tn he blind. 



