42 SMITPISONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



area give attachment to the axillary cords of the wing bases. The 

 posterior margin is deeply inflected laterally in the groove before the 

 metanotum, and is here connected with the arms of the mesothoracic 

 postphragma (fig. 16 C, D, G, 2Ph). 



The phragmata of the insect thorax are primarily infoldings or in- 

 growths of the body wall on the intersegmental lines between the 

 successive notal plates, but in the bee the first phragma is solidly 

 united with the anterior margin of the mesonotum, and thus becomes 

 a mesothoracic prcphragma, while the close association of the second 

 phragma with the posterior margin of the mesonotum gives this 

 phragma the status of a mesothoracic postphragma. A third phragma, 

 usually present between the metanotum and the first abdominal seg- 

 ment, is absent in the bee. The phragmata serve to give increased 

 surfaces of attachment for the intersegmental dorsal muscles, but 

 when two successive phragmata are united with opposite ends of the 

 same segmental plate, the muscles become intrasegmental in their 

 action. 



The prephragma of the mesothorax of the bee is a simple, crescent- 

 shaped ingrowth from the deflected anterior margin of the scutum 

 (fig. 16 B, iPh), separated by a narrow line of intersegmental 

 membrane (fig. ii F, Mh) from the overlapping pronotum. The 

 postphragma, on the other hand, is a large U-shaped sclerite (fig. 

 16 D, 2Ph) projecting far back under the metanotum into the cavity 

 of the propodeum. Its only connections with the mesonotum are 

 the attachments of its basal arms with the lateral ends of the scutellum. 

 The base of each arm splits into an outer and an inner lamella (G) ; 

 the inner lamella {v) is continuous with an infolding of the meso- 

 scutellar margin, the outer lamella («) is reflected back into the 

 anterior margin of the metanotum. The postphragma thus maintains 

 its intersegmental relations, but there is in the bee no representative 

 of the usual postscutellar supporting plate, or postnotum, other than 

 the exposed parts of the inner lamellae of the phragma where the latter 

 join the mesoscutellum. 



The metanotum. — The back plate of the metathorax is a narrow 

 transverse sclerite (fig. i6E), constricted mesally and expanded 

 laterally, closely interpolated between the mesonotum and the pro- 

 podeum (fig. 15, Nz)- The metanotum shows no division into 

 scutum and scutellum, but its widened lateral parts form a prominent 

 triangular area on each side. From the lateral margin of each tri- 

 angular area there is deflected an irregular, semidetached sclerite 

 (fig. 21 E, W3), and before the latter is a smaller independent sclerite 

 {d), both of which sclerites give support to the wing base, as will 



