COLOR CHANGES IN DYNASTES TITYRUS 439 



It might also be imagined that the change was of significance 

 to the beetle in its normal life, since when in the moist wood it 

 is dark and inconspicuous and when active in the light it is light 

 colored and spotted, so that it might very well be protected from 

 observation and detection by enemies as blending with the lights 

 and shades of usual daylight or moonlight illumination of probable 

 backgrounds in nature. 



A number of experiments also suggested that light might act 

 through the eyes in bringing about adaptive coloration. Thus 

 when the beetle was quiet and dark colored, if light from the 

 window shone very long upon one side only, of that animal, it 

 would change to light on that side only, but still later might 

 change to light on the other side also. 



It was evident that of the many factors that might be concerned 

 in the color change, there might be not only the external changes 

 from moist to dry, from darkness to light, from quiet to mechani- 

 cal disturbances, but unknown internal factors associated with 

 the life of the animal. 



To eliminate one after the other of these possible factors, a 

 number of trials were made. It was found that mechanical 

 disturbance alone did not induce color fading, unless there was 

 actual translation of the insect from one part of the glass dish 

 to another, as when it was pulled up to the top by a string at- 

 tached beforehand and operated without changing or opening 

 the closed vessel: and on the other hand, beetles might remain 

 dark colored when verj^ much awake and active ; and they might 

 bleach out when quiet as well as when active. 



The changes from darkness to light seemed at first to be 

 important, but it soon transpired that the beetle could remain 

 dark in the light as well as in the dark, by day or night, and would 

 remain light colored in the dark also. 



The third factor, the change from moist to dry, seemed the 

 decisive one and potent over everything else. Thus beetles kept 

 in a closed glass with dry filter paper, remained light colored 

 day and night but remained dark if the paper was wet. When 

 a beetle was put into a bowl of water it turned dark as far as 



