20a
(18b).    Tarsi with 4 segments; front
and hind wings similar in size, shape and venation 
                       (Figs.A-E)  cerci tiny or absent
[termites]...............................................…........................Isoptera
 
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                            A                               B                                            C                                D                                 E                                                                           
              
 
 
 
20b.    Tarsi with 3 or less segments; hind wings usually shorter than
front wings; cerci either
            present or absent....................................................................................................…................…............
21