Photo: J. J. Ward. 



PART OF THE WING OF A WALL-BUTTERFLY 



Showing how the numerous scales build up its design, not only cover- 

 ing the general surface like the slates on a roof, but arranged in wavy 

 bands and concentric zones. Each microscopic scale is finely striated 

 longitudinally, and the light falling on these undergoes "interference." 

 This gives the metallic iridescence to the wings of many butterflies, 

 greatly enhancing the coloration due to pigment. 



Photo: J. J. Ward. 



CROSS-SECTION OF THE SPINE OF A SEA-URCHIN (Clddris 



Metularia), MAGNIFIED SEVERAL DIAMETERS 



The remarkable feature is the beautiful zoned structure. The 

 spine is a delicate needle to start with, but around this there is 

 a periodic deposition of lime from the skin, one concentric zone after 

 another. It is probable that this kind of architecture gives the 

 spine great stability, but it is primarily an expression of rhythmic 

 orderly growth. It shows that the quality of beauty is not confined 

 to the outsides of animals. 



