92 NATURAL HISTORY OF AQUATIC INSECTS CH. 



Not a few aquatic Beetle larvae breathe after the 

 manner of Hydrobius, though the details of the 

 mechanism exhibit great variety. The larva of the 

 Dipterous fly, Stratiomys, employs the same principle 

 in a somewhat different way. But the closest parallel 

 is furnished by three other Dipterous larvae, those of 



Fig. ji. — Pupa of Hydrobius fuscipes (magnified). The wings, enclosed by the 

 pupal wing-sheaths, are partly e.xtended. 



Dixa, Anopheles, and Pericoma, which are furnished 

 with a respiratory cup much like that of Hydrobius, 

 though more elaborate and more efficient. The 

 older Hydrobius larvae are altogether buoyant, and 

 when out of their depth swim at the surface in a 

 serpentine manner. 



