12 



ENTOMOLOGY 



rarely absent. Abdomen slender, with ten segments and three or two 

 very long multiarticulate cerci. Integument delicate. Nymphs thysa- 



A B 



FIG. 20. Libclliila piilcliclla. A, Last nymphal skin; B, imago. Slightly reduced. 



nuriform, 

 species. 



aquatic. Example, Hexagenia (Fig. 19). Three hundred 



7. Odonata. Metamor- 

 phosis direct. Antennae in- 

 conspicuous, bristle-shaped. 

 Mouth parts mandibulate. 

 Prothorax small. Wings 

 four, elongate, subequal, simi- 

 lar, membranous, minutely 

 reticulate, with a costal joint, 

 or nodus. Abdomen slender, 

 with ten segments. Nymphs 

 thysanuriform, aquatic. Ex- 

 ample, Libellula (Fig. 20). 

 About two thousand species 

 have been described. 



8. Thysanoptera (Phy- 



sopoda). Metamorphosis direct, but including a subpupa stage. 

 Mouth parts suctorial. Prothorax long. Tarsus terminating in a 

 bladder-like organ. Wings present, rudimentary or absent, the two pairs 

 narrow, equal, similar, with few or no veins and fringed with long hairs. 

 Abdomen with ten segments. Minute insects. Example, Euthrips 

 (Fig. 21). About one hundred and fifty species have been des- 

 cribed. 



9. Hemiptera. Metamorphosis direct (excepting male Coccidae). 



FIG. 21. Euthrips tritici. Length, 1.2 mm. 



