INVERTEBRATA. 445 



The wings are folds of the integument supported by 

 thickened branched linear structures called nervures and 

 consisting of a trachea and a blood-vessel. The class is 

 divided into a number of orders distinguished by the 

 structure of the wings and of the mouth-parts ; the prin- 

 cipal of these are the following : 



Order Aptera. Wings entirely absent, body covered 

 with cuticular scales or hairs. Development direct. 



Order Orthoptera. Two pairs of wings, anterior pair 

 more or less tough and thickened. Prothorax free, deve- 

 lopment direct or with incomplete metamorphosis. This 

 order includes Cockroaches, Grasshoppers, Locusts, Stick - 

 and Leaf -insects, and Earwigs. 



Order Neuroptera. Both pairs of wings membranous 

 with numerous reticulated nervures, mouth parts masti- 

 catory, prothorax free. Metamorphosis complete or in- 

 complete. Includes Dragon -flies, May -flies, Ant-lions, 

 Caddis-flies, and Termites or White-ants. 



Order Hemiptera. Proximal half of the anterior wings 

 usually horny and rigid ; mouth parts modified for piercing 

 and sucking. Prothorax free ; metamorphosis incomplete 

 Includes Bugs, Lice, Scale-insects, Plant-lice or Aphides, 

 and Cicadas. 



Order Diptera. Posterior wings rudimentary; mouth 

 parts adapted for piercing and sucking. Prothorax 

 fused with the other segments of the thorax. Meta- 

 morphosis complete. Includes Flies, Grnats, Mosquitos, 

 and Fleas. 



Order Lepidoptera. Both pairs of wings large and 

 covered with scales, not folded. Maxillae forming a spiral 

 sucking-tube. Prothorax fused with mesothorax. Meta- 

 morphosis complete. Includes Butterflies and Moths. 



Order Coleoptera. Anterior wings horny and rigid, 

 acting as covers for the posterior pair. Prothorax free. 

 Mouth parts adapted for biting. Metamorphosis com- 

 plete. Includes true Beetles. 



Order Hymenoptera. Both pairs of wings membranous, 

 hinder pair smaller and attached by hooks to anterior pair, 

 Mouth parts adapted for biting and licking. Prothorax 

 united. Metamorphosis complete. Includes Ants, Bees. 



