Insect Colouring 



Here something occurs analogous to what we 

 see in the higher animals after the removal 

 of the kidneys; the urea at first contained in 

 the blood, in imperceptible quantities ac- 

 cumulates and becomes manifest when the 

 means by which it is eliminated disappear. 



In the larva of the Hydrophilus, on the 

 other hand, the excretions enjoy a free outlet 

 from the beginning; and the urinary products 

 escape as and when formed and are no longer 

 deposited in the adipose tissue. But during 

 the intense labour of the metamorphosis, any 

 excretion becomes impossible; the uric acid 

 must and does collect in the adipose sub- 

 stance of the different larvae. 



It would be out of place, despite its im- 

 portance, to pursue the problem of the uric 

 residues any further. Our subject is color- 

 ation. Let us return to it with the evidence 

 supplied by the Sphex. Her almost trans- 

 parent larva has the neutral tint of fluid white 

 of egg. Under its fine translucid skin there 

 is nothing coloured, save the long digestive 

 pouch, which is swollen a deep purple by the 

 pulp of the consumed Crickets. But against 

 this indefinite, vitreous background the 

 opaque white uric cells stand out distinctly 

 in their myriads; and the effect of this stip- 

 pling is a sketchy but by no means inelegant 

 279 



