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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



pattern of the sternal sclerites in the cockroach (fig. 19) has had much 

 to do with establishing this idea, for students have not recognized 

 that the separated plates here are products of sclerotic degeneration, 

 and that the fundamental structure, as shown best in the prothorax, 

 is the same as in insects with undivided thoracic sterna. While the 

 Blattidae undoubtedly retain some relatively generalized structural 



sa~ 



19. — The thoracic sterna of a cockroach, Blatta orientalis. 



A, general view of the three thoracic sterna and their paired apophyses. B, 

 diagram of typical structure of a sternum. C, diagram of prosternum of Blatta. 

 D, diagram of mesosternum of Blatta. 



Bs, basisternum ; IS, first abdominal sternum ; k, furcal suture ; vS"^, sternal 

 apophysis ; sa, external pit of sternal apophysis ; SI, sternellum ; spn, external 

 pit of spina ; Ss, spinasternum ; S, segmental sternum. 



characters, they are in many respects highly specialized insects adapted 

 to a particular kind of habitat, though to one almost universally dis- 

 tributed. The flattening of the body has been accompanied by a struc- 

 tural alteration in most of the under parts of the thorax, and there is 

 every reason to believe that the sterna, covered as they are by the bases 

 of the legs, have become largely membranized to allow of an inflection 

 of their posterior parts. We should be on very unsafe ground, there- 

 fore, if we take the fragmented condition of the sternal sclerotization 



