COLOR CHANGES IN DYNASTES TITYRUS 455 



mary, or color-containing cuticula, the specialized part of which 

 on the outside may well correspond to such lamellae as he figures 

 for Chrysobothris, and which in Dynastes has the peculiar light- 

 intercepting and moisture-holding structure. The thickness 

 of the colored layer is about 80 ^ and that of the moisture-ab- 

 sorbing lamella about 8 ix. 



SUMMARY 



111 these large beetles there are rapid and striking color changes 

 that may be associated with changes in temperature, changes 

 in illumination, changes in mechanical disturbance and position 

 of the animal. 



Analysis of these factors show that it is the changes in mois- 

 ture which underlie the other conditions that are decisive in 

 bringing about the color changes. 



While it might be imagined that the changes of color were 

 connected with internal nervous changes, such complication 

 is not needed to explain the facts. 



The material composing the outermost layer of the exoskele- 

 ton of the elytra and of the dorsal part of the thorax is such that 

 it readily absorbs and gives off moisture from the air as well as 

 from liquid. When this material absorbs liquids it allows the 

 color of the underlying part of the exoskeleton to be seen as 

 dark red; when the liquid is out of the outermost layer the air 

 that takes its place prevents the color of the underlying part 

 of the shell from being seen and the shell looks light. 



The structure of the shell that thus modifies the light is that 

 of a material whose continuity is interrupted at intervals of less 

 than one micron either by pores or by some other physical 

 arrangement not determined, which makes it like a sponge or a 

 dried and cracked colloid. 



The natural spots on the shell which do not change to light 

 color in drying seem to be formed by the presence in this layer 

 at such areas, of some matter that clogs the pores or fills its inter- 

 stices so that it acts as if permanently wet or impregnated with 

 liquid, and so j^ermits the seeing of the color of the underlying 

 laver. 



