140 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



In most Other insects the second valvifer is articulated directly to 

 the ninth tergum, and has a simple rocking movement on the latter 

 produced by the alternate contraction of its anterior and posterior 

 muscles, because the tergum forms ordinarily a complete dorsal arch 

 over its segment and is relatively immovable. In the Hymenoptera, 

 however, the second valvifer articulates with the first valvifer, which 

 in turn articulates with the ninth tergum, and this interpolation of 

 the first valvifer between the tergum and the second valvifer con- 

 siderably changes the mechanism ; but in the bees a further modifica- 

 tion results from the reduction of the ninth tergum to the pair of 

 lateral quadrate plates which are themselves freely movable because 

 of their membranous connections with the surrounding parts. Ob- 

 servations on the freshly extracted sting of a living bee show that the 

 principal activity in the basal apparatus that accompanies the pro- 

 traction and retraction of the lancets consists of a back-and-forth 

 vibration of the quadrate plates and a quick elevation and depression 

 of the anterior ends of the first valvifers (triangular plates). The 

 second valvifers (oblong plates) remain relatively stationary, but 

 there is sometimes a quivering of the third valvular lobes. 



The working of the mechanism that moves the lancets will be 

 readily understood if a cardboard model is cut out representing the 

 skeletal parts of one-half of the sting apparatus (fig. 48). The first 

 valvifer of the model should be attached by pins to the quadrate plate 

 and to the oblong plate, and the lancet must be twisted so that it will 

 slide against the lower edge of the stylet when the two are held together 

 by a wire loop. We have observed on the living bee that the muscles 

 between the quadrate tergal plate (fig. 47 A, IXT) and the oblong 

 plate {2V If) move the quadrate plate and not the oblong plate. This 

 is just the reverse of the usual interaction of the corresponding plates 

 in other insects. If, therefore, the quadrate plate of the model (fig. 

 48 A, IXT) is moved alternately in the direction of its two antagonistic 

 muscles {17, 18), while the oblong plate (2Vlf) is held stationary, 

 the effect is a simple back-and-forth movement of the lancet on the 

 lower edge of the stylet. Hence, when the posterior muscle (18) 

 contracts, as shown at A, it moves the quadrate plate rearward, and 

 the latter pulls on the dorsal angle (a) of the first valvifer (iVlf), 

 with the result that the valvifer is rotated upward on its ventral 

 angle (b) and retracts the lancet (Let). On the other hand, when the 

 anterior muscle (ly) contracts, as at B, the quadrate plate is pulled 

 forward and rotates the valvifer downward, which movement pro- 

 tracts the lancet. It is possible that the slender muscle (A, 7^) from 

 the spiracular plate to the posterior end of the first valvifer may be 

 an accessory retractor of the lancet, as supposed by Kraepelin. 



