INSECT ABDOMEN SNODGRASS 



135 



ments of the entire basal part of the sting apparatus. The latter, 

 however, does not move back and forth horizontally in the position 

 of repose (fig. 46 A) ; on the contrary, the whole structure, including 

 the valvifers and the quadrate plates of the ninth segment, swings 

 downward and posteriorly on the upper angles of the quadrate plates, 

 and the shaft, which at the same time is unsheathed and depressed, 



Fig. 46. — Relative positions of the parts of the sting of a worker bee, Apis 

 mellifica, in repose and action. 



A, sting in usual position within the sting chamber. 



B, end of abdomen bent down, shaft of sting unsheathed and partly depressed 

 ready for extrusion. 



C, basal part of sting apparatus swung posteriorly as indicated by arrow, 

 sting fully depressed and extruded. 



D, usual position of basal parts of sting, ninth tergal plates, and spiracular 

 plates of eighth segment within the sting chamber during repose. 



E, position of same parts when shaft of sting is fully protruded. 



is driven out from the sting chamber at the tip of the abdomen (B, C). 

 By a reverse set of movements in the basal apparatus the sting is 

 retracted and elevated to its initial horizontal position and ensheathed 

 between the second valvifers and their distal lobes. Conversely, it 

 can be demonstrated on a freshly killed specimen that back-and- forth 

 movements of the shaft involve these same swinging movements of 

 the basal apparatus. The free movement of the basal parts is made 

 possible by the membranous connections of the latter with the sur- 



