I AQUATIC BEETLES 73 



because they were unable to free themselves from the 

 larval integument. 



" In the damp earth which the pupa requires, the 

 hooks described above fulfil a purpose unexpected by 

 us, but at the same time of great importance. The 

 skin of the pupa is very delicate. Lying on damp 

 earth it could hardly escape injury, and the weight of 

 the body might easily give it a distorted shape. But 

 the pupa protects itself from these dangers by assum- 

 ing an unusual attitude. It extends itself back 

 downwards in a horizontal position, and supports the 

 weight of its body by the three sets of hooks as upon 

 a tripod. In this attitude, though surrounded on all 

 sides by moist earth, it keeps its body from actual 

 contact with any object until it has assumed its final 

 shape. 



" Thus we see how necessary are those hooks, 

 which at first sight appeared so useless. To decide 

 that this or that structure is superfluous because we 

 cannot guess its use is truly ridiculous in beings 

 whose information is so limited as ours." 



Lyonnet's observations on the attitude of the pupa 

 and the use of the hooks are confirmed by the later 

 observations of Miger. The pupa of Hydrobius sup- 

 ports itself upon the floor of its cell in a similar way, 

 though here the spines cover the whole of the back. 



" The pupa," continues Lyonnet, " is provided with 

 spiracles along the sides of the body, and these lead 

 us to suppose that it changes its mode of respiration, 

 and breathes in the pupal stage, not by the tail, but 

 by the sides of the body, as in many other Insects. 



" When the time for the last transformation arrives, 



