192 ARTHROPOD A. 



extremity and sending a pair of arms or arches from its base, 

 which normally bend ventrally, but are here forced to the sides. 

 At its extremity each of these arches enlarges to form a rather 

 large flattened plate, the sheath plate, to which strong muscles 

 are attached. 



(6) A pair of lancets which are fastened to the dorsal surface 

 of the sheath and the sheath arches by tongue and groove joints 

 (each tongue is enlarged along its inner margin so that it is held 

 firmly in the groove). Each lancet is pointed at its free extrem- 

 ity, and its sides near the point are set with bai^bs that point 

 toward the base of the sting. The arch of each lancet is con- 

 tinued past the end of the corresponding sheath arch, and is 

 there articulated to one corner of a somewhat triangular plate. 

 The remaining corners of each are articulated respectively to 

 the large sheath plate and to another plate, the oval plate. 

 Determine the attachment of the muscles to the plates and find 

 what movements of the lancet the contraction of the different 

 sets of muscles would cause. Note that the lancets are elastic 

 and bend easily. 



The large muscles attached to the sheath plates were attached 

 to the wall of the abdomen and function to give the thrust that 

 sets the sting. After the sting is drawn from the body of the bee 

 the muscles attached to the plates continue active, and the sting 

 works deeper and deeper in. Understand why it works in instead 

 of out. 



2. Lying near the base of the shaft is a large poison sac or 

 reservoir, which is very muscular. It receives its poison from 

 the poison gland, a long and narrow coiled tube that is bifurcated 

 near its free end. It discharges the poison by means of the 

 contraction of the muscles of its walls through a rather large, 

 short duct into the space inclosed by the sheath and the two 

 barbs. Each barb bears a prominence that serves as an injector, 

 which moves backward and forward with the barb to which it 

 is attached, in an enlargement of the basal portion of the sheath. 

 It may be seen in the preparation. In this way poison is forced 

 into the wound. Poison may also be admitted to the cavities 



