412 INSECTA. 



interior of those attached to the maxillae are wanting, or are not 

 developed in several, and particularly the larger species. The thorax 

 is short and transversal. The elytra are obtuse and truncated at 

 their posterior extremity, leaving the anus exposed, which ends in a 

 point. The two anterior legs are long, slender, folded in two, and 

 when contracted, almost at a right angle with the body: they are 

 terminated by a very short, strongly compressed tarsus, the inferior 

 surface of which, in the males, is furnished with a fine compact brush. 

 The four others are broad and extremely thin, the joints of their 

 tarsi forming little leaflets arranged like a flounce. 



The Gyrini are usually small, or of a moderate size. They are to 

 be found from the very beginning of spring until the end of autumn, 

 on the surface of stagnant waters, and even on that of the Ocean, 

 where, frequently collected in troops, they appear like brilliant 

 points, swimming and wheeling with great agility in all sorts of 

 curves, and in every direction, whence the name of Puce aquatique 

 and Tourniquet given to them by authors. Sometimes they remain 

 motionless, but the instant any one approaches, they escape by 

 swimming, and dive with great celerity. Their four last legs serve 

 them as oars, and the two before for seizing their prey. Placed on 

 water, the superior surface of their body is always dry, and when 

 they dive, a little bubble of air, resembling a silvery globule, remains 

 fixed to its posterior extremity. When seized, a lacteous fluid 

 oozes from their body which spreads over it, and which, perhaps, 

 produces that disagreeable and penetrating odour they then diffuse, 

 and which remains attached to the fingers for a long time. They 

 copulate on the surface of the water. Sometimes they remain at the 

 bottom clinging to plants : there, also, it is probable they secrete 

 themselves to pass the winter *. 



G. natator, L. ; Panz., Faun. Insect. Germ. Ill, 5; De Geer, 

 Insect., IV, xiii, 4, 19. Three lines in length ; oval, glabrous, 

 very glossy; bronze-black above; black beneath; legs fulvous; 

 scutel triangular, very pointed, somewhat longer than wide; 

 elytra rounded at the extremity, and marked with small 

 impressed puncta in regular and longitudinal lines. 



The female lays her eggs on aquatic plants. They are very 

 small, and form little yellowish white cylinders. The body of 

 the larva is long, tapering, linear, and consists of thirteen annuli, 

 each of the three first bearing a pair of legs. The head is 

 large, of an elongated oval shape, and much flattened, pre- 

 senting the same parts as that of the larva of a Dytiscus ; but 

 here the fourth and seven following annuli are furnished on each 

 side with a conical, membranous, flexible filament with bearded 

 edges. The twelfth ring has four similar, but much longer 

 ones, directed more posteriorly. Two very slender tracheae 

 traverse the whole length of the body, and receive an air vessel 



* M. Leon Dufour, Ann. des Sc. Nat., Oct. 1821, has published some anatomical 

 observations on these Insects. The small intestine is remarkable for its length. The 

 caecum is not lateral as in Dysticus. The genital organs of the males differ from 

 those of the other Carnivora. 



