COLOR CHANGES IN DYNASTES TITYRUS 453 



orange tint. These minute shavings are very hydroscopic so 

 that when breathed on they quickly curl up and quickly lie 

 down again flat when the moist air passes away. 



Under higher powers, Zeiss 4. D, the shavings seem made of 

 parallel pyramids or cones that are subdivided or forked toward 

 the surface and there end in large granules or pieces of the sur- 

 face. The appearance is as if the surface of the shell were per- 

 forated by vertical canals or pores between constituent cones or 

 clubs of yellow material, resembling to some extent, a cheese 

 with regular pores in place of irregular cavities. The edges of 

 pieces of these shavings under Zeiss 4 ocular and 2 mm. seem to 

 be made up largely of granules about 0.6 m ii^ diameter. 



Structure of elytra 



Raising the elytra they are seen to be all yellow on the under 

 or inner side next the body, but the light coming through the 

 translucent elytra is red. Thus the substance of the elytra, 

 both outside and inside is yellow by reflected light but red by 

 light that passes through. Adding water to the inner face of 

 the elytra does not change its color nor does it soak into the 

 shell. It is only the outer surface of the elytra that is both 

 absorptive and changeable in color. 



The long veins on the under side of the elytra mark out areas 

 that are filled with small yellow vesicles or air bags, in some 

 regions crowded together, in others scattered, and seemingly 

 expansions of terminal twigs of the trachea. WTiere these yellow 

 vesicles are crowded together, that is, toward the median line, 

 they show marked red dots scattered between them. 



When pieces of shell are removed for section they absorb 

 the fixing liquid, and though they remain yellow on the inner 

 surface, they turn uniformly red on the outer surface, since the 

 former yellow areas now change to red on the entrance of the 

 liquid. 



Vertical sections through the elytra (fig. 4) show that the large 

 central air spaces are lined by a thin epidermis, and that the 

 upper and lower skeletal layers are connected together by fre- 



