NO. O INSECT ABDOMEN SNODGRASS I3I 



12. Occlusor of the spiracle. — A short, relatively broad muscle in 

 the worker arising dorsally on marginal ridge of spiracular plate, 

 with fibers convergent ventrally to insertion on lower end of closing 

 valve of eighth spiracle (fig. 43 B) ; in the queen this muscle attached 

 as usual to both ends of spiracular valve (fig. 44 C). 



/J. Dilator of the spiracle. — A slender muscle arising on anterior 

 ventral part of spiracular plate, crossing the plate obliquely to inser- 

 tion on lower end of closing valve of spiracle (figs. 43 B, 44 C). 



14. Tergovalvifer muscle.— A long muscle, horizontal in the usual 

 position. Origin posteriorly on ventral margin of spiracular plate in 

 the worker (fig. 43 B), on inner face of posterior lobe of plate in the 

 queen (fig. 44 C) ; insertion anteriorly on posterior end of first valvi- 

 fer (figs. 42 A, 45 A). This muscle is the only representative in the 

 bee of the usual tergal muscles of the first valvifer. 



13. First tergoventral muscle. — A slender muscle, present only in 

 the queen, arising on anterior lobe of spiracular plate (fig. 44 C) ; 

 extends mesally and anteriorly to dorsal wall of median pouch of 

 genital chamber anterior to duct of spermatheca (B). 



16. Second tergoventral muscle. — Similar to the last and present 

 only in the queen. Origin just behind 15 on spiracular plate (fig. 

 44 C) ; insertion on dorsal wall of median pouch of genital chamber 

 posterior to spermathecal duct (B). 



It will be observed that there are 1 1 muscles, including the spiracu- 

 lar muscles, attached on each of the spiracular plates of the eighth 

 tergum in the queen (fig. 44 C), and eight in the worker (fig. 43 B). 

 Morison (1927) says there are nine in the worker, but he describes 

 a small muscle from the antero-ventral margin of the plate to the side 

 of the quadrate plate, which was not observed by Betts (1923), and 

 which the writer has been unable to find. It is evident that the spiracu- 

 lar plates are important parts of the general sting mechanism, but 

 since the muscles from them to the parts of the eighth and ninth 

 segments that compose the sting apparatus are all small, it is probable 

 that they do not produce any of the major activities of the latter. 



The muscles of the ninth segment include the principal muscles of 

 the stinging mechanism, and the muscles of the proctiger. Their dis- 

 tribution and functions have been discussed particularly by Sollmann 

 (1863), Kraepelin (1873), Zander (1911), and Snodgrass (1933). 

 These muscles are as follows, on each side : 



//. Anterior tergal muscle of the second valmfer (fig. 45 A). — A 

 large tergopleural muscle composed of two distinct bundles of fibers, 

 one dorsal (lya), the other ventral (lyb). Fibers of dorsal group 



