50 NATURAL HISTORY OF AQUATIC INSECTS CH. 



temporar}' pupa-skin. The head is bent forwards 

 upon the thorax, while the legs and wings are dis- 

 posed s)'mmetricall}- on each side of it. There are 

 spines on the prothorax of the pupa, resembling 

 those of the Hydrophilus pupa, but far smaller. 



At length the full-formed Beetle creeps out from 

 its dark cell. Though its ultimate form is now 

 attained, the new skin is at first soft and pale- 

 coloured. A week passes before it completely 

 assumes the dark chestnut colour, the polished 

 surface, and the firm texture which it is destined to 



Fig. 8. — Dytiscus marginalis (male), showing suckers on fore legs and smooth 



elytra. 



acquire. The outline of the body as seen from above 

 is regularly oval. The back is gently rounded, the 

 under side angulated along the middle line. The 



