NO. 2 HONEY BEE SNODGRASS 97 



to propel the poison through the poison canal when the sting is in 

 action. Finally we must note a small forked rod, the furcula (E, Frc, 

 F), that projects into the body cavity at the base of the bulb above 

 the neck of the poison sack. The furcula is an apodemal structure 

 giving attachment to important muscles of the sting (B, Frc). 



When the sting is not in use it is concealed within the abdomen, 

 where its base is supported in the membranous wall of the sting 

 chamber, and the upper angles of the quadrate plates are loosely 

 articulated on the spiracular plates of the eighth segment (fig. 32 A). 

 The shaft is turned upward on the rami so that the bulb is encased 

 in the membranous fold between the oblong plates, and the distal part 

 is clasped by the sheath lobes. When the sting goes into action, the 

 whole structure is swung downward and posteriorly on the dorsal 

 angles of the quadrate plates (a) until the basal apparatus takes a 

 vetrical position with the sheath lobes directed upward (fig. 32 B) ; 

 simultaneously the shaft is depressed and, by the backward swing of 

 the sting base, is protracted from the tip of the abdomen. The lancets 

 now begin a rapid, alternate back-and-forth movement on the stylet. 

 The action of the sting thus involves three separate movements : first 

 the backward swing of the entire organ, second the depression of the 

 shaft, third the movement of the lancets. On retraction of the sting, 

 the shaft is replaced in the sheath, and the base returns to the position 

 of repose. 



The backward swing of the entire organ in the sting chamber was 

 attributed by the writer in a former paper (1933) to pressure sup- 

 posedly engendered within the abdomen by contraction of the ab- 

 dominal segments. More recently, however, Rietschel (1937) has 

 shown that specifically it is the depression of the seventh abdominal 

 sternum that projects the sting. Manipulation of a dead specimen, in 

 fact, will demonstrate that when the seventh sternum is turned down- 

 ward, its broad anterior part, turning upward and backward, is 

 pressed deeply into the abdomen against the base of the sting and 

 forces the latter to swing posteriorly. The shaft, of course, is not 

 protracted by this action, since it must at the same time be turned at 

 right angles to the supporting apparatus. The depression of the shaft 

 is effected by a pair of large, flat muscles arising on the inner surfaces 

 of the oblong plates (fig. 31 B, ip/) that curve anteriorly and mesally 

 over the base of the bulb and are inserted on the furcula (Frc). The 

 tension of these muscles on the furcula pulls upward on the base of 

 the bulb (fig. 32 C), and the shaft is turned downward on a pair of 

 fulcral points (h) at the lower angles of the bulb that abut against 

 small lobes on the lower ends of the second rami {2r). The fulcral 



