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PARTS OF THE THORAX. 



The three divisions or segments of the thorax vary much 

 in size and shape. It is interesting to note the coordinated 

 specialization of wings and corresponding thoracic segments. 

 The great development of the forewings in Anosia is attended 

 by a corresponding marked development of the mesothorax ; 

 and the reduction of the flight value of the hind wings is 

 paralleled by the reduction in size and importance of the 

 metathorax. The prothorax is altogether much reduced in 

 size and function. Its legs are small and weak. 



PROTHORAX. 



The prothorax is visible as a narrow ring or collar im- 

 mediately caudad of the head. On the dorsum may be 

 noted two prominent tumid portions, the " prothoracic lobes ' ' 

 of Scudder, and caudad of these, and mesad, a small tri- 

 angular plate ; the tumid lobes constitute the scutum and 

 the triangular plate is the scutellum. Just caudad of the 

 scutellum are two lobes (smaller than the Scudderian lobes) 

 connected by a transverse piece. These lobes and trans- 

 versa bar are the postscutellum. The prczscutum is obsolete. 

 The pleura and sternum are united without visible sutures, 

 forming a "continuous ossified collar" encircling the pro- 

 thorax beneath. 



MESOTHORAX. 



The greatly developed mesothorax forms fully five-sixths 

 of the mass of the thorax. The prothorax is distinctly sep- 

 arate from the other thoracic segments, and is movable ; 

 but the meso- and metathoracic segments are much more in- 

 timately united. 



Dorsal aspect. — The dorsum of the mesothorax quite 

 overshadows the metadorsum, and plainly shows two sclerites, 

 the scutum and scute/turn. (A third, the postscutellum, is 

 hidden beneath the metathoracic scutum. ) 



