346 1NSECTA. 



and propels its body forward ; the latter is usually terminated by two conical, 

 bearded, and moveable filaments. 



These larvae suspend themselves on the surface of the water by means of 

 two lateral appendages at the extremity of their body, which they keep above 

 it. When they wish to change their position, they communicate a sudden 

 vermicular motion to their body, and strike the water with their tail. They 

 feed more particularly on the larva; of the Libellula 1 , and those of the Culices 

 and Aselli. When the period of their metamorphosis has arrived, they issue 

 from the water, and having gained the shore, penetrate into the earth, which 

 must, however, be constantly moistened, or very humid. They then excavate 

 an oval cavity, and shut themselves up in it. 



According to Rcesel, the eggs of the D. marginalis are hatched from ten to 

 twelve days after they are laid. In four or five days after this epoch, the larva 

 is already five lines in length, and undergoes its first change of tegument. The 

 second ensues at the expiration of a similar period, and the animal is then 

 double its former size. Its final length is two inches. They have been ob- 

 served, in summer, to enter into their pupa at the end of fifteen days, and to 

 become perfect insects in fifteen or twenty more. 



This great genus is now divided into several, Dytiscus proper, Colymbctes, 

 Hygrobia, &c. 



The second genus of the Hydrocanthari, or the 



GYRINUS, Linnaus, 



Comprises those in which the antennae are clavate and shorter than the head ; 

 the two first legs are long and project like arms; the remaining four are com- 

 pressed, wide, and pinnate. There are four eyes. 



The body is oval and usually very glossy. The second joint of the antenna 1 , 

 which are inserted in a cavity before the eyes, is prolonged exteriorly in the 

 form of an auricle, and the following joints are very short, crowded, and united 

 in one almost fusiform and slightly curved mass. The head is sunk in the 

 thorax almost to the eyes, which are large, and divided by a border, in such a 

 way that two are above and two underneath. The labrum is rounded and 

 strongly ciliated before. The palpi are very small, and the interior of those 

 attached to the maxillae are wanting, or are not developed in several, and par- 

 ticularly the larger species. The thorax is short and transversal. The elytra 

 are obtuse and truncated at their posterior extremity, leaving the extremity 

 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 



