150 



NATURAL HISTORY OF ARTHROPODS. 



is external, the larvae breathing by three leaf-like gills containing finely-branching air- 

 tubes. 



The most striking peculiarity of the larval dragon-fly is the nature of the labium or 

 under lip. This is greatly enlarged and bent, so that at rest it forms a broad, smooth 

 mask covering the jaws. When any small insect approaches, the array of jaws and 

 accessory jaws is unmasked, the under lip being darted out after the prey. The under 



Fig. 217. — Metamorplioses of dragon-flies. 1 larva, and 2, larval skin of JEschna; 3, larva, 4, moulting, and 



5, adult of Libellula dejiressa. 



lip thus serves as a mask, and also as a grappling-iron to seize the ^-ictim, as it is armed 

 at the extremity, with a pair of hooks, by which the struggling insect is firmly held 

 and irresistibly' drawn to the mouth, where it is torn to fragments by the sharp 

 jaws. This structure is well shown in the adjacent figure. 



The pupal dragon-fly differs from the larva only in possessing the rudiments of 

 wings, which are like long, slender pads on the back. " When 

 the insect is about to assume the pupa state, the body, having 

 outgrown the larva skin, by a strong muscular effort opens a 

 i-ent along the back of the thorax, and the insect, having fas- 

 tened its claws into some object at the bottom of the pool, the 

 pupa gi-adually works its way out of the larva skin. It is now 

 considerably larger than before. Immediately after this tedious 

 operation its body is soft, but the crust soon hardens. This 

 change, with most species, probably occurs early in summer." 



" When about to change into the adult fly the pupa climbs 

 up some plant near the surface of the water. Again its back 

 yawns wide open, and from the rent our dragon-fly slowly 

 emerges. For one hour or more it remains torpid and list- 

 less, with its flabby, soft wings remaining motionless. The 

 fluids leave the surface, the crust hardens and dries, rich and 

 varied tints appear, and the dragon-fly rises into its new world 

 of light and sunshine." (Guide to the Study of Insects.) 



The Odonata are divided into three groups; the lowest, called Agrionina, and 

 represented by the genus Agrion, comprises small, slender-bodied, delicate forms, 



Fig. 218.— Pupa of 

 JEschna. 



