NO. O INSECT ABDOMEN SNODGRASS 125 



muscles (lo, ii) from its upper end, and with the first valvifer by 

 a single muscle (14) from its lower margin. 



The quadrate plates, or lateral tergal sclerites of the ninth dorsum 

 (fig. 41, IXT), are the suspensory plates of the sting mechanism. 

 Because of their membranous dorsal connections they are freely mova- 

 ble on their upper angles (/) within the overlapping spiracular plates. 

 Each quadrate plate is a large four-sided sclerite, articulated anteriorly 

 with the dorsal posterior angle (a) of the first valvifer (iVlf). Its 

 dorsal part projects into the body cavity as a flat apodemal extension 

 (Ap) on which important muscles of the sting mechanism are at- 

 tached ; its lower edge overlaps the second valvifer {2'Vlf), with which 

 it is connected by a membranous fold of the integument. 



The triangular plate, or first valvifer (fig. 41, iVlf), is a relatively 

 small sclerite lying anterior to the quadrate plate. Its anterior angle 

 (c) is continuous with the upper end of the ramus of the lancet, or 

 first valvula (rivl), and its posterior angles {a, b) articulate respec- 

 tively with the anterior angle of the quadrate plate (IXT) and the 

 dorsal margin of the second valvifer, or oblong plate {2Vlf). The 

 single muscle of the first valvifer, which arises on the lower margin 

 of the spiracular plate (fig. 43 B, 14), is inserted on the upper edge of 

 the valvifer very near the posterior dorsal angle (fig. 42 A, 14). In 

 the usual position the muscle is horizontal. 



The oblong plate, or second valvifer (fig. 41, 2Vlf), lies beneath 

 the first valvifer and the quadrate plate. Its articulation with the 

 lower posterior angle of the first valvifer {b) is somewhat before 

 the middle of its dorsal margin. Its anterior end is narrowed and con- 

 tinuous with the ramus of the second valvula {2rvl) ; posteriorly it 

 supports the third valvula (jF/), which in the bee is a short, soft, 

 mostly membranous appendage. 



The oblong plates of opposite sides are connected medially by an 

 ample membrane thickly clothed with hairs, which represents the 

 venter of the ninth segment. The membrane is ordinarily arched up- 

 ward above the base of the sting (fig. 45 A, IXV), forming below it a 

 deep cavity in which the bulb of the sting is ensheathed, but, when the 

 sting is depressed, the membrane is partly everted and appears 

 as a hairy pad over the bulb (fig. 41, IXV). 



The shaft of the sting is composed of the united second valvulae 

 (fig. 41, 2VI), and of the slender first valvulae, or lancets {iVl). 

 The single dorsal piece, formed of the second valvulae, is enlarged 

 basally as the bulb of the sting {bib) ; its distal tapering part is the 

 stylet {stl). The lancets slide freely on the lateral ventral margins 

 of the bulb and stylet (fig. 42 E) ; their lower edges are in contact. 



