COLOR CHANGES IN DYNASTES TITYRUS 441 



Such local and rapid changes in the light might be due to 

 some photochemical change. That this is not probable seems 

 to follow from the following. When the beetle is exposed to 

 the light of a naked mazda bulb shining through 7 cm. of water 

 the color bleaching is very much retarded, in fact not till the 

 water becomes decidedly warm does the bleaching effect appear. 

 Again, a beetle exposed to dark rays only, through black paper, 

 may be bleached by the heat. It was therefore thought probable 

 that the action of the light might be explained as due to its heat- 

 ing the surface of the beetle and thus altering the moisture 

 conditions, either by drying off the moisture in the beetle directly, 

 or by increasing the moisture holding power of the air next 

 the beetle and thus making it less saturated and so leading to 

 drying off of the beetle's surface. 



In like manner, the results of pulling a beetle to the top of a 

 dish of air saturated at the bottom by wet paper, might be to 

 bleach it from its being thus brought into dryer air, and other 

 experiments in which mechanical disturbances appeared to cause 

 bleaching could also be explained as the result of change of air 

 and consequent loss of moisture. 



When the light colored beetle is exposed to wet air, it be- 

 comes dark but slowly; often thirty minutes seems to make no 

 change though careful observation may reveal a sooty appear- 

 ance within five minutes, but if left one hour or two hours, both 

 thorax and elytra may be dark. In some cases, however, the 

 elytra changed noticeably in three minutes, and in six minutes 

 were all dark red. 



If the beetle is floating in water it may become dark in one 

 minute, when, however, the beetle crawls about so that the shell 

 is in contact with wet paper, the change from light to dark may 

 be completed in five minutes, and if moist paper is actually 

 pressed upon the thorax or the elytra, the region so moistened 

 may turn dark in a second. 



On the other hand, when the dark beetle in a saturated atmos- 

 phere is exposed to the ordinary air of the room, the rate of turn- 

 ing light is rapid but differs in different cases according to the 



THE JOURNAL OF EXPERIMENTAL ZOOLOGV. VOL. 20, NO. 3 



