290 Insects and their Surroundings 



them a small air-bubble ; the film which encloses 

 this stretches from the tip of the wing-covers to the 

 hinder end of the abdomen. They are not, like the 

 pond-skaters, completely enveloped in air while 

 under water. 



The Beetles of a nearly-related family (Dyticidae) 

 belong to the group of insects which live habitually 

 submerged. Their elongate shape and their smooth 

 rounded contours are admirably adapted for motion 



Fig. 158. — Water-Beetle (Dyticus 

 and pupa (3). Natural size. 



iiialis, L.), with its eggs (i), larva (2), 



through the water, but there is no dense hairy 

 covering as in the pond-skaters to ensure the forma- 

 tion of an air-bubble ; the breathing of the Dyticids 

 while under water is provided for in quite another 

 way. The abdominal spiracles open on the upper 

 surface of the segments, which are completely covered 

 by the wing-cases when the wings are shut. The 

 wing-cases being convex and the upper surface of 



