KEY TO PHYLA 25 



19 (20) First and second pairs of wings of nearly the same 



length. Tarsi three jointed order odonata 



20 (19) Second pair of wings either small or wanting. Tarsi 



four jointed order ephemerida 



21 (18) Antennae usually conspicuous 22 



22 (23) Tarsi two or three jointed. Second pair of wings 



broader at base than first pair or at least as large as the 

 first pair order plecoptera 



23 (22) Tarsi four jointed. Wings equal in size 



order isoptera 



24 (17) Tarsi with five segments. Abdomen with hair-like, 



many jointed, anal filaments.. ..order ephemerida (in part) 



25 (6) Wings wanting, or in some cases immovable, rudimen- 

 tary wings are enclosed in sacs, called the wing pads 26 



26 (27) With typically three pairs of legs. Head, thorax, and 



abdomen usually distinct ; head always distinct. General 

 body form resembling that of adult insects, class insecta 

 (nymphs, larvae, pupae, and a few wingless adults) 28 



27 (26) Usually with four pairs of legs; in some cases with 



two or three pairs, but in these, head, thorax, and abdomen 

 are all fused together. Respiration never by means of gills. 

 class arachnida 



28 (33) Abdomen bearing prolegs on at least some somites.... 29 



29 (30) Abdomen with five pairs of prolegs and with no spir- 



acles at apex of abdomen order lepidoptera (larvae) 



30 (29) Prolegs on last abdominal somite only 31 



31 (32) Abdominal segments each with a pair of long lateral 



filaments or provided with conspicuous tufts 



order neuroptera (larvae) 



