320 INSECTA. 



They pass their first and last stage of existence in the fresh and 

 placid waters of lakes, marshes, ponds, &c. They are good 

 swimmers, and rise occasionally to the surface of their liquid 

 abodes in order to respire ; this they easily effect by keep- 

 ing their legs motionless, and permitting themselves to float. 

 Their body being reversed, they elevate its posterior extrem- 

 ity a little above the water, raise the extremity of their ely- 

 tra, or depress the end of the abdomen, in order that air may 

 enter the stigmata, which are covered by them, whence it 

 finds its way to the tracheae. They are excessively vora- 

 cious, and feed on small animals inhabiting the same element, 

 which they never leave excepting during the night, or at its 

 approach. When taken from the water they diffuse a nause- 

 ating odour. They are frequently attracted into houses by 

 the light of candles, &c. 



Their larvae have a long and narrow body composed of 

 twelve rings, the first of which is the largest ; a stout head, 

 provided with two powerful mandibles, curved into an arc, 

 and perforated near the point; small antennae, palpi, and six 

 simple approximated eyes on each side. They have six tol- 

 erably long legs, frequently fringed with hairs, and termi- 

 nated by two small nails. They are active, carnivorous, and 

 respire either by the anus or by a kind of fins resembling 

 branchiae. When about to enter into their pupa state they 

 leave the water. 



This tribe consists of two principal genera. 



Dytiscus, Geoff. 



The Dytisci have filiform antennae longer than the head, two eyes, 

 the anterior legs shorter than the following ones, and the last most 

 commonly terminated by a compressed tarsus ending in a point(l). 

 By means of their legs fringed with long hairs, the two last particu- 



(1) According to M. Leon Dufour, their crop is terminated behind by an annu- 

 lar roll (bourrelet) a character not found in the preceding tribe. Their caecum 

 forms a natatory bladder. Their pectus contauis two pneumatic sacs, while the 

 tracheae of the other parts are tubular. The adipose splanchnic tissue possesses 

 the characters of a true epiploon or mesentery. Their stigmata also differ from 

 those of the Terrestrial Carnivora. 



