112 BEES AND WASPS [CH. 



abruptly upwards : between them is interposed a 

 bulbous mass of muscles (not shown in the figure) 

 attached to the front end of the director. Finally 

 the needles are articulated to strong levers which 

 give attachment to powerful muscles. When the 

 handle of the lever is pulled down by these muscles, 

 in the direction shown by the arrows in the figure, 

 the arm which articulates with the needle is thrust 

 backward and slightly upward, and the needle itself 

 is driven along the groove of the director so as to 

 project beyond it, escaping at a spot just short of its 

 extremity. 



In the act of stinging the first incision is made by 

 the point of the "director" itself, which is darted out 

 by the action of its own levers and muscles : a strong 

 piece of horny material (S. fig. 18) on its upper sur- 

 face at first holds the "director" firmly down, but 

 eventually, when full extrusion has been reached, 

 causes the "director" and "needles" to turn abruptly 

 upwards. This action causes a slight enlargement of 

 the wound beneath the surface. Then by a rapid 

 alternate movement of the levers the "needles" are 

 driven in yet deeper. The two concave inner faces of 

 the " needles " are pressed firmly against each other, 

 partly by the tapering sides of the "director" and 

 partly by the course imparted by the muscles, and 

 so form a closed tube between them. Down this 

 tube the poison is driven by the contractions of the 



