TRACHEATA 347 



with the end of her abdomen, and depositing an egg at each 

 dip, or in other species she deposits the eggs on submerged 

 water-plants. 



The larvae are very voracious, and feed upon other insects, 

 their lower lip or labium is peculiarly modified into a structure 

 known as the " mask," this can be suddenly shot out, and serves 

 to capture food. The larva of Agrion has at the end of its 

 abdomen three leaf-like gills, but other species breathe by their 

 rectum, the walls of which are richly supplied with tracheae. 

 The entrance and exit of the water is controlled by three valves, 

 which can be opened or closed at will ; in some species the 

 sudden expulsion of water serves to propel the larva through 

 the water. This anal respiration recalls a similar change of 

 function of the posterior part of the alimentary canal in some 

 Crustacea (see p. 268). The pupa stage, which precedes the 

 imago, is in the Libellulidae an active stage, and is sometimes 

 termed the "nymph" (Fig. 196). 



Family 5. Mykmeleontidae. — The ant-lion, Myrmeleo, in 

 the imago condition has clubbed antennae, a small prothorax, 

 a large mesothorax, 

 and wings of equal 

 size. The larvae live 

 at the bottom of 

 little conical sandy 

 pits, which they ex- 

 cavate ; they lie par- 

 tially embedded in 



the sand at the bot- ^^^_ i97._Ant-lion, Mynndeonf^icaHus. 



torn of the pit, and 



seize with their powerful mandibles any insect, etc., which 

 happens to stray over the edge. The mouth is closed, 

 and the food is sucked in through perforations in the 

 mandibles. It is stated that the proctodaeum of the larva 

 does not open into the alimentary canal, but is modified to 

 form a silk gland, which serves for the spinning of the cocoon 

 in which the pupa envelops itself. 



Family 6. In the Family Hemekobiidae the larvae of 

 Uhrysopa and Hemerdbius, which are known as Aphis Hons, feed 

 on Aphides. They also have the proctodaeum modified to form 



