COLKOPTEKA. 321 



larly, they are enabled to swim with great velocity. They dart 

 upon other Insects, aquatic Worms, &c. In most of the males the 

 three first joints of the four anterior tarsi are widened and spongy 

 underneath; those of the first pair particularly are very remarkable 

 in the larger species, these three joints forming there a large palette, 

 the inferior surface of which is covered by little bodies, some in the 

 form of papillae, and others, larger, in that of cups or suckers, &c. 

 Some of the females are distinguished from their males by their 

 sulcated elytra. The body of the larva is composed of from eleven 

 to twelve annuli, and covered with a squamous plate; this larva is 

 long, ventricose in the middle, and slender at each end, particu- 

 larly behind, where the last annuli form an elongated cone furnished 

 on the sides with a fringe of floating hairs, with which the animal 

 acts on the water, and propels its body forwards; the latter is usu- 

 ally terminated by two conical, bearded and movable filaments. Be- 

 tween them are two small cylindrical bodies, perforated at their ex- 

 tremity by a hole, which are so many air-ducts, and in which the 

 two tracheae terminate; stigmata, however, are observed on the sides 

 of the abdomen. The head is large, oval, attached to the thorax by 

 a neck, and furnished with strongly arcuated mandibles, under the 

 extremity of which De Geer perceived a longitudinal slit, so that, in 

 this respect, these organs resemble the mandibles of the larva of the 

 Myrmeleon, and serve as suckers; the mouth, however, is provided 

 with maxillae and a labium with palpi. Each of the three first annuli 

 bears a pair of tolerably long legs, the tibiae and tarsi of which are 

 bordered with hairs which afford them additional aid in swimming. 

 The first ring is the largest or longest, and is defended above as well 

 as underneath by a squamous plate. 



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 posi- 

 tion, they communicate a sudden vermicular motion to their body, 

 and strike the water with their tail. They feed more particularly on 

 the larvae of the Libellulae, 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 hu- 

 mid. 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 under- 

 goes its first change of tegument. The second ensues at the expi- 

 Vol. III. 2 Q 



