THE HVDROnEPHAGA. 



265 



attacks. They possess this peculiarity in their larva 

 state, — that, although furnished with capacious jaws, they 

 do not masticate their food; for these jaws are merely 

 prehensile organs, and are tubular and perforated towards 

 the extremity : their acuteness wounds the prey caught, 

 which is then sucked dry through this tube. Their 

 progression in the water is effected in jerks or springs, 

 caused by the sudden expansion of their bent tapering 

 tails; and they direct it with that precision, as to pounce 

 as readily upon their prey as a cat does on a mouse. 

 The perfect insect, if not alarmed, is stately in its 

 motions, — proceeding always in an oblique direction 

 through the water, to the top of which it frequently 

 comes for the purpose of inhaling fresh atmospheric 

 air ; this it does by protruding the apex of the elytra 

 above the surface, and thus receives beneath them a 

 quantity sufficient for the supply of the spiracles which 

 are situated there. The small genera, such as Haliplus, 

 Cnemidotus, Hydroporus, Pcelobius, &c., are much more 

 active than the larger ones, and move about with the 

 greatest velocity in every direction, sporting with each 

 other in the merriest gambols. Cnemidotus presents a 

 remarkable singularity in the structure of the posterior 

 coxae, which are dilated externally into a thin plate, be- 

 neath which they receive and conceal the posterior legs. 

 We have associated with this family, the Gyrini, or 

 whirlwigs; thus named from their habit of swimming 

 in circles upon the surface of the water. Their acti- 

 vity is excessive and incessant ; and the structure and 

 combination of their muscular fibre must be remarkable, 

 to admit of such interminable and rapid motion. The 

 whole structure of the larva and imago, also, is very dif- 

 ferent to that of the preceding section of the family: 

 thu-s, in the perfect insect, the antennae are thick and 

 fusiform, with a large auriculated joint at their base ; 

 their legs are considerably dilated and compressed, — the 

 anterior being the longest and most slender, evidently 

 for prehension; and the posterior tarsi consist of laminae 

 folding apparently upon one joint. Their larva is 



