364 LAKES AND STREAMS 



silver - white beneath, and has one angulated dorsal fin. The brook - lamprey 

 (P. branchialis), which, unlike the other species, is distributed all over the Northern 

 Hemisphere, and spends all its life in brooks and small streams, is bluish green 

 above and whitish beneath, with two dorsal tins which join, and a mouth-opening 

 as broad as the head. 



*~ h Zu-\ 



THK RIVEB-LA11PBEY. 



Brown Water- Passing on to the consideration of the aquatic insects and those 



Beetle. living near the water, a few of the carnivorous ground-beetles fre- 

 quenting hedges and banks claim first attention. The species most commonly met 

 with is the common shore-beetle {Elaphrus ri/iarius), which is of a bronzy green 

 colour with red legs, and the wing-covers adorned with four rows of violet eye- 

 like spots. A distant relative, the great brown water-beetle (Dytisms ivaiyi mil in), 

 belongs to a carnivorous family, feeding exclusively on aquatic organisms. 

 Distinguished from other water - beetles by its thread-like feelers, which are 

 carried open even in the water, this insect is from 1 to l\ inches long, dark 

 olive-green above and yellow below, with a yellow crescent near the tips of the 

 elytra. When caught in a net with other creatures, in a mass of mud and water- 

 plants, it soon attracts attention by its restless behaviour ; but when in its usual 

 haunts, and not flying from one stretch of water to another, is by no means 

 conspicuous, as it keeps under water. It is obliged, however, to come frequently 

 to the surface to breathe, and as most of the breathing-apertures are situated under 

 the wings, near the hind extremity, it raises the lower end of the body out of the 

 water for the purpose of respiration, lifting the wing-covers slightly and holding 

 the head obliquely downwards ; if disturbed it dives at once. The process of respira- 

 tion is rapidly performed, and, as the breathing-apertures are generally large, such 

 a quantity of air is inhaled that the beetle becomes very light and has to make 

 great efforts to sink, its diving being generally oblique and scarcely ever in a per- 

 pendicular direction. Only the hind-legs are used in swimming ; the legs of the 



