CLASSIFICATION 



FIG. 17. 



tera) and Embiidae being transferred doubtfully to Orthop- 

 tera. 



Enderlein's recent and thorough studies confirm the view 

 that Termitidse, Embiidae, Psocidse and Mallophaga constitute 

 a single order. 



5. Plecoptera. Metamorphosis direct. Antennae long, 

 multiarticulate. Mouth parts mandibulate. Prothorax large. 

 Wings two pairs, membranous, coarsely and complexly reticu- 

 late; equal or else hind wings larger 

 and with an ample plicate anal area. 

 Abdomen with ten segments and usu- 

 ally a pair of long multiarticulate cerci. 

 Nymphs thysanuriform, aquatic; adults 

 unique in having tracheal gills. Ex- 

 ample, Pteronarcys (Fig. 18).' A 

 single family, Perlidae, comprising two 

 hundred species. 



6. Ephemerida. - - Metamorphosis 

 direct. Antennae bristle-like. Mouth 

 parts mandibulate, but atrophied in 

 the adult. Prothorax small. Wings 

 membranous, minutely reticulate; hind 

 pair much the smaller, rarely absent. 

 Abdomen slender, with ten segments 

 and three or two very long multi- 

 articulate cerci. Integument delicate. Nymphs thysanuri- 

 form, aquatic. Example, Hexagenia (Fig. 19). Three hun- 

 dred species. 



7. Odonata. Metamorphosis direct. Antennae inconspicu- 

 ous, bristle-shaped. Mouth parts mandibulate. Prothorax 

 small. Wings four, elongate, subequal, similar, membranous, 

 minutely reticulate, with a costal joint, or nodus. Abdomen 

 slender, with ten segments. Nymphs thysanuriform, aquatic. 

 Example, Libellula (Fig. 20). About two thousand species 

 have been described. 



8. Thysanoptera (Physopoda). Metamorphosis direct. 



A chicken louse, Menopon. 

 Length, 2 mm. 



