ORDER COLEOPTERA. 245 



The head is large, oval, attached to the corslet by a neck, 

 with mandibles very much arched, and under the extremity 

 of which De Geer has perceived a longitudinal cleft, so that 

 m this respect these organs resemble the mandibles of the 

 larvas of antlions, and serve as suckers. The mouth, never- 

 theless, presents jaws and a labrum, with palpi. The first 

 three rings have each a pair of feet, tolerably long, the 

 leg and tarsus of which are bordered with hairs, which are 

 also useful in swimming. The first ring is larger or longer, 

 and defended underneath, as well as above, by a scaly plate. 



These larvae suspend themselves to the surface of the water 

 by means of two lateral appendages at the end of their tail, 

 and which they keep dry. When they desire suddenly to 

 change place, they give to their body a prompt and vermicu- 

 lar motion, and strike the water with their tail. They are 

 nourished more particularly with the larvae of gnats, stipulse, 

 libellulae, asselli, &c. When the time of their transforma- 

 tion is come they quit the water, gain the shore, and bury 

 themselves in the ground ; but it must be always moistened, 

 or very humid. They there form an oval cavity, in which 

 they shut themselves up. 



According to Roesel, the eggs of the dytiscus marginalis 

 exclude the young in ten or twelve days after the laying. 

 At the end of from four to five days the larva is already 

 four or five lines in length, and moults for the first time. 

 The second change of skin takes place at the end of an in- 

 terval of the same duration, and the animal is as large 

 again. The length of two inches is the limit of its growth. 

 In summer it has been observed to change into the nymph- 

 state at the end of fifteen days, and into the perfect insect, 

 fifteen or twenty days afterwards. Besides the cloaca of the 

 insects of this family, the dytisci have a coecum tolerably 

 long, which is perceptible in the larva state. 



This great genus is subdivided as follows : 



