KEY TO CLASSES AND ORDERS OF ANIMALS 31 



12(1) With two pairs of wings. 13 



13(22) The two pairs of wings unlike in structure. 14 



14(15) Front wings leathery at base and membranous at the 

 tip, often overlapping. Mouth parts formed for 

 sucking. (Comstock, 121; Lutz, 80.) 



Order Hemiptera 



15(14) Front wings of the same texture throughout. 16 



16(19) Front wings horny or leathery and apparently veinless; 

 wing covers or elytra. i7 



17(18) Abdomen with caudal appendages in the form of 

 movable forceps. (Comstock, 102; Lutz, 61.) 



Order Euplexoptera or Dermaptera 



18(17) Abdomen without forcep-like appendages. (Com- 

 stock, 494; Lutz, 280 and 498.) Order Coleoptera 



19(16) Front wings leathery or parchment-like with a network 

 of veins. ^^ 



20(21) Under wings not folded, sucking mouth parts. (Com- 

 stock, 121; Lutz, 95.) Order Hemiptera 



21(20) Under wings folded lengthwise, biting mouth parts. 

 (Comstock, 104; Lutz, 62.) Order Orthoptera 



22(13) The two pairs of wings similar and membranous. 23 



23(24) Last joint of tarsi bladder-like or hooflike in form and 

 without claws. (Comstock, 119; Lutz, 79.) 



Order Physopoda or Thysanoptera 



24(23) Last joint of tarsi not bladder-like. 25 



25(26) Wings entirely or for the most part covered with scales. 

 Mouth parts formed for sucking. (Comstock, 191; 

 Lutz, 115.) Order Lepidoptera 



26(25) Wings naked, transparent, or thinly clothed with 

 hairs. ^7 



