THE CLASSIFICATION OF INSECTS 69 



segments, are seen to slope forward in such a manner 

 that the coxa? of the legs are brought close together under 

 the insect's head, while the bases of the wings are carried 

 backward. By this means, all of the legs are thrust for- 

 ward beneath the mouth, where they serve as a kind of 

 basket for catching and holding prey. All dragon-flies 

 possess four wings, which are approximately equal in size 

 and form. The membrane of the wing is glassy in tex- 

 ture, and is traversed by a complex network of veins. 

 Dragon-flies are also remarkable for the great length of 

 the abdomen, which is relatively longer than in any other 

 insect. The nymphs are entirely aquatic, and feed upon 

 insects, snails, or indeed any creature with which they are 

 strong enough to grapple. For the capture of their prey, 

 they are provided with a unique development of the 

 second maxillae, or labium, called the " mask." This 

 structure, when not in use, lies folded beneath the head ; 

 but it is jointed, and can be shot out with great rapidity, 

 the prey being seized by means of terminal hooks and 

 drawn back to the mouth. Although the nymphs differ 

 markedly in appearance from the adult, metamorphosis 

 is incomplete, for there is no motionless pupa state. The 

 full-fed nymph climbs up the stem of a water plant, 

 its skin splits dorsally, and the winged insect appears. 

 Dragon -flies are represented in all parts of the world, 

 except the far northern regions. Over forty species are 

 found in Britain. 



Order IX. — Thysanoptera. 



These insects are known popularly as thrips. They 

 are very small, and usually frequent flowers. The man- 

 dibles and first maxilla? are modified as piercers, and when 

 in conjunction serve for sucking the juices of plants. 



