44° ANIMAL RESPIRATION 



the wing-cases. This space serves as a reservoir for air, which 

 the beetle carries about with it under water, and renews from time 

 to time by coming to the surface and pushing out the hinder end 

 of its body. At the same time air is taken into the last pair of 

 breathing-pores, which are much enlarged and equivalent to those 

 present in the larva. 



The little Whirligig Beetles {Gyrinus), which may often be 

 seen moving about in an erratic manner on the surface of ponds 

 and streams, are in the habit of diving when alarmed, carrying 

 down a bubble of air with them which enables breathing; to go 

 on during submersion, and prevents water from getting into the 

 breathing-pores. The Great Black Water- Beetle iyHydrophilus 

 piceus) lives under water, and carries air about in a manner 

 different from that described for Dytiscus. A large part of the 

 body is covered with closely-set down, in which air is entangled, 

 so that the breathing-pores are kept dry and are able to carry on 

 their work. This air, of course, requires renewal from time to time, 

 and there is a remarkable kind of adaptation by which this can be 

 manao;ed without the Beetle having to leave the water. For the 

 ends of the feelers (antennae) are broad and hairy so as to fit them 

 for acting as ladles, by means of which air-bubbles are dragged 

 under water and applied to the downy surface of the body, to 

 which they adhere. 



Interesting breathing arrangements are found in some of the 

 Water- Bugs, which are either purely aquatic or live chiefly on 

 the surface. Pond- Skaters {^Hydrometridce) are of the latter kind, 

 and almost everyone must have seen them moving swiftly about 

 in the way that has suggested their name. Like the Whirligig 

 Beetles, they are able to dive, at which time they are completely 

 surrounded by a film of air, which sticks closely to the velvety 

 surface of their bodies. It is, however, easy to drown them. 

 The Water- Boatmen {^Notonectidce), which swim actively about 

 on their backs, are also provided with an arrangement of hairs, 

 enabling them to carry a supply of air under water. 



The ravenous Water- Scorpions [Nepidcs) are thoroughly 

 aquatic in habit. Both in the broad fiat kind {Nepd) and the 

 lean hungry -looking one [Ranatrd) the only breathing -pores 

 present are placed at the tip of the tail, from which projects a 

 long narrow tube composed of two closely-interlocking halves. 

 It is supposed that the tip of this organ is protruded from time 



