50 Afinah Entomological Society of America [Vol. IX, 



tergum of insects simply by the inward projecting phragmas. 

 In some insects the postscutellum is completely separated from 

 the scutoscutellum by membrane. (Fig. 10, psl). 



The old view that the tergum of adult insects consists of four 

 consecutive transverse plates was proposed by Audouin, '24. 

 He termed these plates the presecutum, scutum, scutellum and 

 postscutellum, and this terminology has been retained though 

 Audouin's general conception of the tergum, held until recently 

 by most entomologists, is now obsolete. Other writers have 

 given various names to the different tergal regions. Amans, '85, 

 proposed the terms prodorsum, dorsum, postdorsum and sub- 

 postdorsum for the identical sclerites previously termed pre- 

 scutum, scutum, scutellum and postscutellum by Audouin. 

 Audouin's terminology has the right of priority, is widely 

 accepted, has no undesirable features and should therefore stand. 



Wings. The wings of insects arise in two ways. In hemi- 

 metabolous insects .they appear as outgrowths at the lateral 

 margins of the meso- and metanotum. In holometabolous 

 forms, they arise internally as the so-called wing-buds, appear- 

 ing externally at or after pupation. At first the wings are filled 

 with tracheae, blood, tissue, etc. The trachese persist and are 

 ultimately replaced by the veins or nervures of the adult insect 

 wing, which serve as stiffening supports for the wing mem- 

 brane. The blood and tissue gradually disappear and the two 

 lateral surfaces of the sac-like outgrowth come together, forming 

 the wing membrane. 



The wings of adult insects are connected with the scuto- 

 scutellum along its lateral margin, on the lateral margin of the 

 tergum. They articulate with the pre- and post-alar processes, 

 together with the small alar sclerites at the base of the wing 

 (Fig. 10, pra, poa, sa, ba). Beneath they articulate with 

 the pleural wing process (Fig. 10, plwp). 



The wings are variously modified in different insects, 

 forming the elytra of Coleoptera, the tegmina of Orthoptera, 

 the halteres of Diptera, the hemielytra of Hemiptera and the 

 hairy and scaly wings of Lepidoptera and Trichoptera. In 

 :such forms as Carabidas, Ptinid^, and weevils the hind wings 

 .are often lacking, owing to disuse, and the elytra in some forms 

 fuse together thereby forming a solid covering for the hind 

 wings (if present) and the abdomen. The general belief 

 has always been that elytra are modified wings. 



