COLOR CHANGES IN DYNASTES TITYRUS 451 



lating areas or appearances: minute regions of fiery red and of 

 green in juxtaposition as if from refraction of light due to some 

 minute lack of continuity of the substance of the shell. 



These optical appearances seem beneath a surface pellicle. 

 When a needle point is pressed along this surface, it leaves a 

 groove that is mottled with dark and light as if some spongy or 

 powdery structure had been crushed in, and these structural 

 changes remain, so that it is possible to write dark lines on the 

 yellow background by compressing the material near the surface. 



When minute water-drops from a single hair of a camels- 

 hair brush are placed on the surface, they sink in and spread 

 in the shell to vanish at once as if they had spread in some dry 

 powder. The edges of the advancing water within the shell 

 are sinuous, that is, the water does not spread entirely with 

 the same speed all along the edge of the drop. Where deep 

 grooves are made by pressure of the needle the water does not 

 enter readily but it goes in elsewhere and spreads thence. A 

 larger area may take thirty seconds to be blotched over with 

 black clouds as the water enters here and there and spreads. 



That the light color is due to some way in which air is held 

 within the shell structure seems indicated again by the fact 

 that burnishing the surface with a blunt ivory point produced 

 a permanent dark area, as if the material had been brought 

 together and the air expelled. 



Possibly then, many of the minute dark pits on the surface 

 of the animal may have arisen as results of pinching of the sur- 

 face by legs or horns of other beetles or by other mechanical 

 compressions. 



With needle sharpened as a chisel, the material of the shell 

 can be shaved off as yellow shavings that look, under the micro- 

 scope, to be waxy masses full of minute granules. Digging 

 deeper shows more and more of the same material, and the 

 bottom of the excavation is black with scintillating points as 

 if it were a compounded structure. Water put into these minute 

 excavations sinks down into the black bottom material. The 

 shavings from regions of the shell that are not yellow but are 

 red spots differ from the yellow only in somewhat darker, more 



