KEY TO CLASSES AND ORDERS OF ANIMALS 37 



36(41) With biting-mouth parts. 37 



37(40) With long filamentous caudal setae; labium not longer 

 than the head, and not folded on itself like a hinge. 38 



38(39) Gills mainly under the thorax; tarsal claws two; caudal 

 setae two. Stone flies. (W. and W., 883; Lutz, 50.) 



Plecoptera 



39(38) Gills mainly on the sides of the abdomen; tarsal 

 claws single; caudal setae generally three. (May 

 flies. (W. and W., 921; Comstock, 86; Lutz, 40.) 



Order Plectoptera or Ephemerida 



40(37) Caudal setae represented by three broad, leaflike respir- 

 atory plates traversed by tracheae, or by small spi- 

 nous appendages; labium when extended much longer 

 than the head; at rest, folded like a hinge, extending 

 between the bases of the fore legs. (Damsel flies and 

 dragon flies. (W. and W., 928; Lutz, 42; Comstock, 

 89.) Order Odonata 



41(36) Mouth parts combined into a jointed beak, which is 

 directed beneath the head backward between the 

 fore legs. Bugs. (W. and W., 933; Lutz, 95; Com- 

 stock, 121.) Order Hemiptera 



Class I N S E C T A 



LARVAE 



Tentative key to the orders of true larvae. Wings develop 

 internally; pass through a quiescent pupal stage. Key to land 

 forms compiled by V. E. Shelf ord; aquatic forms from J. G. 

 Needham. 



1(29) With jointed thoracic legs. 2 



2(11) Aquatic forms, i.e., forms capable of living beneath the 

 water. 3 



