The Glow-Worm and Other Beetles 



istry is not yet in a position to demonstrate, 

 with its reagents, the common origin of the 

 two substances, at least the most convincing 

 analogies point to it. 



In this delicate problem of the insect's col- 

 ouring, one single point thus far comes within 

 the domain of observed facts : the progressive 

 advance of chromatic evolution. The car- 

 buncle of the Dung-Beetle of the Pampas 

 suggested the question. Let us then inquire 

 of his near neighbours, who will perhaps en- 

 able us to advance a step farther. 



Newly stripped of his cast-off nymphal 

 skin, the Sacred Beetle possesses a strange 

 costume, bearing no resemblance to the ebony 

 black which will be the portion of the ma- 

 ture insect. The head, legs and thorax are 

 a bright rusty red; the wing-cases and abdo- 

 men are white. As a colour, the red is al- 

 most that of the Spurge Caterpillar, but it is 

 the result of a dye on which nitric acid has 

 no effect as a detector of urates. The same 

 chromatic principle must certainly exist in a 

 more elaborate form and under a different 

 molecular arrangement in the skin of the 

 abdomen and the wing-cases which will 

 presently replace white by red. 



In two or three days the colourless be- 

 comes the coloured, a process whose rapidity 



