The Glow-Worm and Other Beetles 



slide, they do not dissolve nor produce effer- 

 vescence. Uric acid then is not present in 

 this case ; and the substance must be guanine, 

 an alkaloid known to be the urinary product 

 of the Spiders. The same is true of the yel- 

 low, black, purple or orange pigment that 

 forms a coating under the skin. In short, 

 by utilizing, in a different chemical combina- 

 tion, the waste products of animal oxidiza- 

 tion, the magnificent Spider rivals the mag- 

 nificent caterpillar; she beautifies herself with 

 guanine as the other does with its uric acid. 



Let us abridge this dry subject; let us be 

 content with these few data, which could if 

 necessary be corroborated by many others. 

 What does the little that we have learnt 

 teach us? It tells us that the materials re- 

 jected by the organism, guanine, uric acid 

 and other dross from life's refinery, play an 

 important part in the coloration of the in- 

 sect. 



Two cases are distinguishable, according 

 as the colour is dyed or simply painted. The 

 skin, Itself colourless and transparent, Is In 

 places Illumined by a coloured varnish, which 

 can be removed by a touch with a paint- 

 brush. Here we have paint, the result of 

 the urinary compound laid on the inner sur- 

 face of the covering, just as the chromatic 

 286 



