Entomology of the Illinois River, 163^ 



A. NyTTijphs. 

 With biting mouth parts. 



Maxillae and mandibles retracted, apices only visible; 

 minute semi-aquatic air breathers. 



(Spring-tails) Thysanura. 

 Maxillae and mandibles prominent; water breathers, 

 usually with tracheal gills. 

 Abdomen with terminal setae. 



Gills on thorax; setae usually two. 



(Stone-flies) Plecoptera. 

 Gills on side of abdomen; setae usually three. 



(May-flies) Epheinerida. 

 Abdomen without terminal setae, and with ter- 

 minal flat gill-plates or internal gills. 



(Dragon-flies) Odonata, 

 With jointed beak; air breathers. 



(True Bugs) Hemiptera. 



B. LarvcB. 



With jointed thoracic legs. 



False legs wanting (except in a Philhydrus, which 

 has six pairs present) ; not living in a case. 

 Filamentous gills wanting— present but not seg- 

 mented in Berosus and Gyrinidae, segmented in 

 Cnemidotus, in which the legs have but one claw; 

 abdomen usually with terminal spiracles. 



( Beetlies ) Coleoptera. 

 Body with segmented filamentous gills; no spiracles 

 at apex of abdomen; two claws on legs. 



Neuroptera, 



A pair of false legs on last segment, each with one 



or two strong claws; usually in a tubular case. 



(Case- flies) Trichoptera. 



Five pairs of false legs, provided at their apex with 



numerous booklets; no spiracles at apex of 



abdomen. (Caterpillars) Lepidoptera. 



Without jointed thoracic legs. (Flies) Diptera. 



