WATEE-BBETLES. 201 



atmosplieric disturbances, and during storms to descend to tlie 

 bottom of the water, only rising towards the surface as the 

 weather becomes calmer. 



The bodies of the DytiseidoB are generally smooth and ovate, 

 and the different parts of the body, as a rule, fit into each 

 other. The eyes do not project. The hind-legs are long and 

 fringed, and the feet are broad and also fringed. The antennse, 

 as before mentioned, are long and slender. The anterior tarsi 

 of the fore-legs of the males are frequently more or less 

 widened, and the elytra of the female are sometimes fmTOwed 

 or sulcated. 



When these beetles hibernate or are at rest, they retire 

 into the masses of aquatic plants or into the mud at the 

 bottom of the water. They all breathe atmospheric air, and 

 are therefore obliged to come frequently to the face of the 

 water. Their manner of respiration is very interesting. The 

 upper part of their abdomen is provided with breathing tubes 

 or spiracles, which are hidden by the elytra when the insects 

 are not flying. The back of the abdomen is nearly flat ; 

 above it the elytra when shut form a kind of arch, and thus 

 inclose the spiracles in a chamber, hito which water cannot 

 enter to wet the wings inclosed withiu. When the beetles 

 wish to take a supply of air they gently protrude the 

 extremities of their bodies above the water, and allow the air 

 to enter the chamber upon their backs. The air so obtained 

 can enter the spiracles as the beetles require it, and thus they 

 are able to remain in the depths of the water until all the 

 supply of air has been utilised, when they are again obliged 

 to return to the surface for more. If, for some reason or 

 other — such as their antennse being held by the valves of a 

 mussel, of which I have read — the insects cannot return to 

 the surface of the water, they, though aquatic, will be 

 drowned, and sooner, it is said, than even land-beetles under 

 the same circumstances. As these beetles swim to and fro 

 under the water, a small bubble of air is seen attached to 

 their extremities. 



The tanks in which the DytiscidcB are confined should be 

 kept covered. Carnivorous beetles while in the aquarium 



