ENTOMOLOGY 



6. Plecoptera. Metamorphosis direct. Antennae filiform, long, 

 multiarticulate. Mouth parts mandibulate. Prothorax large. Wings 



FIG. 2i.Libellulapulchella. A, last nymphal skin; B, imago. Slightly reduced. 



two pairs, membranous, coarsely and complexly reticulate; equal or 

 else hind wings larger and with an ample plicate anal area. Abdomen 



with ten segments and usually 

 a pair of long multiarticulate 

 cerci. Integument soft. 

 ) ^/^^fe Nymphs thysanuriform, 



aquatic; adults unique in 

 having tracheal gills. The 

 stone-flies. Example, Ptero- 

 narcys (Fig. 19). A single 

 family, Perlidae, comprising 

 two hundred species. 



7. Ephemerida. Meta- 

 morphosis 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 multiarticulate caudal filaments (a pair of cerci, with 

 often a median pseudocercus). Integument delicate. Nymphs thysa- 

 nuriform, aquatic, with lateral gills. May-flies, or sand-flies. Exam- 

 ple, Hexagenia (Fig. 20). Three hundred species. 



8. Odonata. Metamorphosis direct. Head mobile; eyes large. 

 Antennae inconspicuous, bristle-shaped. Mouth parts mandibulate. 

 Prothorax small, free; meso- and metathorax intimately united. 

 Tarsi three-segmented. Wings four, elongate, subequal, similar, mem- 



FIG. 22. Euthrips tritici. Length, 1.2 mm. 



