88 NATURAL HISTORY OF AQUATIC INSECTS CH. 



inch in length. The body has the oval convex form 

 and shiny surface of a Hydrophilus. The ventral 

 surface is overspread by a bubble of air. The antennae 

 are clubbed, and used in respiration as in Hydrophilus. 

 On close examination, however, it will be found that 

 the sharp spine, which projects backwards from the 

 under side of the last thoracic segment of the great 

 Hydrophilus, has disappeared in the smaller Beetle, 

 which is the Hydrobius fuscipes of entomologists. 



In spring and early summer the full-grown Beetles 

 are abundant. They become scarce in July, and 

 about a month later the new generation, distinguished 

 for a time by the much lighter colour, makes its 

 appearance. In cold weather they bury themselves 

 in the mud. On watching a living Hydrobius, we 

 shall see it bring the cleft between the head and 

 thorax to the surface of the water when it requires to 

 breathe. Here a small funnel-shaped depression forms, 

 and leads air to the ventral surface. The antenna lies 

 in the cleft, and is apparently employed just as in 

 Hydrophilus, though the small size of the Beetle 

 renders it difficult to affirm this with absolute cer- 

 tainty. Living as it does in very shallow water, 

 Hydrobius finds it easy to expose the under side of 

 its abdomen to the air. When this is done, the 

 watery film bursts, and respiration goes on freely. 

 Whether by accident or of set purpose, the Beetle 

 often executes this movement. Even when floating 

 on deep water, it can turn on its back and throw 

 off the water from its abdomen. 



The following note, together with a good deal of 

 other information respecting Hydrobius, I owe to 



