BLATTODEA. 



65 



Amongst the various species, too, there is much 

 diversity in their length compared with that of the 

 abdomen, being longer in some, abbreviated in others, 

 while from some species they are absent altogether. 

 In certain cases the wings are less fully developed 

 than the elytra, while the length of these appendages 

 may be different in the two sexes. It might seem 

 that here we have a ready means of grouping the 

 various genera and species, but in practice it is found 

 that the relative development of the alar organs is of 



FIG. 12. Elytron and wing of Periplaneta americana. sc, subcosta ; 

 r, radius ; in, medius ; cu, cubitus ; la, first anal nervure ; aa, 

 anal area containing the remaining anal nervures. 1, area between 

 margin and subcosta ; 2, area between subcosta and radius; 3, area 

 between radius and first anal nervure. 



slight importance, as indeed is the case throughout 

 the Orthoptera. 



In accordance with recent nomenclature of insect 

 wing-neuration the following, omitting the costa, are 

 the main nervures of the elytron of a cockroach : 



1. The subcosta, in some descriptions called the mediastinal 

 nervure. 



2. The radius. 

 o. The medius. 



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