NO. 8 INSECT ABDOMEN SNODGRASS 137 



rate plates, and the shaft is correspondingly protruded and withdrawn. 

 It is possible that the strong contraction of the seventh abdominal 

 segment, which elevates the broad anterior lobes of the sternum, may 

 cause the latter to press directly on the base of the sting, but if this 

 is partly accountable for the sting protraction it is only a minor factor. 

 Kraepelin's account of the mechanism of protraction and retraction of 

 the sting seems to have made little impression on other students of 

 the bee, for all subsequent writers appear to assume that the outward 

 thrust of the shaft is caused by the muscles of the furcula arising on 

 the second valvifers. 



While, then, we can explain the protraction and retraction of the 

 sting only as the result of a bulblike action of the abdomen, it is not 

 true that any compression of the abdomen, either in a living bee or a 

 freshly killed specimen, will exsert the sting. The movement of pro- 

 traction in the basal apparatus must be accompanied by a depression 

 of the distal part of the shaft ; otherwise the latter will be simply 

 tilted upward with the sheath. 



The depression of the shaft during the outward thrust and its eleva- 

 tion with the reverse movement are brought about by a special mechan- 

 ism of the basal apparatus, which includes the furcula, the furcular 

 muscles, the rami, the ramus muscles, and the articular points between 

 the base of the bulb and the distal lobes of the rami. It is curious 

 that all students of the mechanism of the bee's sting, since KraepeHn 

 (1873), have regarded the furcular muscles as the protractors (Vor- 

 stossmuskeln) of the shaft. An examination of the sting structure 

 shows at once that the shaft of the organ can have no horizontal move- 

 ment between the second valvifers (oblong plates), on which the 

 furcular muscles are attached, except what little motion might result 

 from the flattening of the rami. Furthermore, a backward pull on 

 the furcula in the direction of its muscles (fig. 47 B, ip) has an im- 

 mediate response in the depression of the distal end of the shaft (C). 

 The fulcra of the vertical movements of the shaft are the points of 

 articulation between the basal processes of the bulb and the distal 

 lobes of the second rami (fig. 42 B, C, 47 B, s). When the shaft is 

 turned down (fig. 47 C) the curves of the rami are flattened, and 

 the ramus muscles (20), which are attached on the basal processes of 

 the bulb distal to the fulcra (s), are stretched. The ramus muscles, 

 therefore, are the antagonists of the furcular muscles (ip) and 

 serve to elevate the shaft and to restore it to its position of repose 

 between the second valvifers and their distal lobes. 



The third set of movements in the sting apparatus, namely, the 

 movements of the lancets on the stylet, has to do with the penetration 



