182 INSECT TRANSFORMATION 



Dragon-fly larvae are aquatic, breathing by means of an air- 

 tube network in the wall of the hind-intestine, or by cerci, in 

 addition to a median tail-filament, transformed into tracheal 

 gills at the tail end. The labium is modified into a protrusible 

 seizing organ (" mask "). The mature nymph leaves the water 

 and becomes changed into the winged adult. 



Sub-ClaSS III. ENDOPTERYGOTA 



The great majority of these insects are winged, the wingless 

 condition of some being clearly secondary. The newly-hatched 

 young is always a larva differing more or less markedly from 

 its parent, and no trace of wings is usually to be seen externally 

 through the various stages of larval life, because the wing- 

 rudiments formed in the second and third thoracic segments 

 at an early stage in the life-history, grow in pouches pushed 

 in from the body-wall, so that they are not covered by cuticle. 

 The legs and other organs of the winged adult are similarly 

 formed in the larva from in pushed imaginal discs or buds. 

 These, pushed out during the last larval stage, become revealed 

 in the pupa a usually quiescent instar which does not feed. 

 During the pupal period there may be a greater or less degree 

 of internal reconstruction in the insect in preparation for the 

 adult condition. 



Nine orders of living insects are included among the 

 Endopterygota. 



Order 15. Coleoptera 



The Coleoptera (or beetles) have biting mandibles, maxillae 

 with all typical parts, and a labium in which the fusion between 

 the two component appendages is close. The prothorax is 

 freely movable on the segments behind. The forewings, hard 

 and firm in texture, are modified as sheaths (elytra) beneath 

 which the membranous hindwings can be folded when at rest. 

 (Many beetles have these hindwings so far reduced as to be 

 incapable of flight.) 



The larvae of beetles show great variety of form, ranging 

 from active, armoured, long-legged campodeiform grubs to 

 soft-cuticled cruciform larvae in which legs are short or absent. 



