162 ARTHROPODA. 



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

 ity, and its sides near the point are set with barbs 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. Deter- 

 mine 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. You must understand that the lancets 

 are elastic and bend quite 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 shoal h. 

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

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

 of the lancets, which are hollow, and escape through minute pores 

 near the barbs. 



3. Lying near the base of the shaft of the sting, sometimes 

 covered by the poison sac, may nearly always be found the last 

 pair of abdominal ganglia, from which nerves may be traced to 

 the muscles that are attached to the plates. 



Understand the whole mechanism, how it is operated and 

 its use. 



