TO THEIR SURROUNDINGS 67 



isolated, the color of each being affected by that 

 part of the surroundings which were made up of 

 the dark bodies of its neighbors. In endeavor- 

 ing to discover whether the sensitiveness of the 

 clirysalids to their surroundings was due to the 

 general surface of the skin as a whole or only to 

 that of one portion, experiments were made by 

 confining the clirysalids in tubes, part of which 

 were colored black and part gilt, and the two parts 

 separated by a diaphragm only permitting the 

 pendent body to pass through ; by reversing the 

 conditions and making experiments with a large 

 number of chrysalids, it became plainly evident 

 that the color influence acted on some element of 

 the larval skin, and that the larger the area of the 

 skin exposed to any one color the more the chrysa- 

 lids followed its influence. The nature of the 

 effects produced is thus described by Poulton : — 



" The coloring matter of the dark pupae is contained 

 in a thin superficial layer of the cuticle ; below this is a 

 thicker layer divided into exceedingly delicate lamellae, 

 between which fluids are present, and the latter form 

 the thin plates which, by causing interference of light, 

 produce the brilliant metallic appearance. The thinner 

 upper layer, being dark, acts as a screen in the dark 

 pupae. Precisely the same metallic appearances are 



