KEY TO CLASSES AND ORDERS OF ANIMALS 29 



4(3) Legs capable of being employed in locomotion; active 

 feeding forms, wing rudiments present or absent. 5 



5(6) Wing rudiments present; nymphs and adults with 

 rudimentary wings, in part. p. 34 



6(5) Wing rudiments absent. 7 



7(8) Mouth parts either combined into a movable beak 

 or in part modified into a mask longer than the head 

 folding on itself like a hinge. Nymphs, in part. p. 34 



8(7) Mouth parts not of the types described in ''7." 9 



9(10) Abdomen and dorsal part of the thorax usually very, 

 weakly chitinized as compared with the rest of the 

 body; generally soft and fleshy. Abdomen when 

 strongly chitinized more than twice as long as the 

 thorax and head together. Larvae of insects with a 

 complete metamorphosis, in part. P- 37 



10(9) Body evenly and usually strongly chitinized; abdomen 

 less than twice as long as the head and thorax together. 



II 



11(12) Mandibles longer than the greatest dimension of the 

 head. Larvae, in part. p. 37 



12(11) Mandibles not longer than the greatest dimension of 

 the head. 13 



13(14) Terrestrial or aquatic; when aquatic gills or lateral 

 filaments not present on the abdomen. Nymphs, in 

 part, chiefly very young, and wingless adults. p. 34 



14(13) GUIs or lateral filaments present on the abdomen. 15 



15(16) Paired lateral filaments which are usually respiratory 

 in function and never leaflike or biramous, present on 

 nearly all the abdominal segments. Nymphs, in 

 part. p. 34 



16(15) Gills present on the abdomen but when paired and 

 lateral always either leaflike or biramous. Nymphs, 

 in part. p. 34 



