86 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



of the muscles of the dorsal and ventral diaphragms, may be classed 

 as intertergal dorsal muscles, tergosternal lateral muscles, intersternal 

 ventral muscles, and spiracular muscles. The dorsals and ventrals 

 again include internal and external groups of fibers, and the internal 

 dorsal and ventral muscles comprise median and lateral muscles. 

 • For a study of the abdomnial musculature segment V of the 

 worker may be taken as a representative segment (fig. 28 A, V), the 

 larger muscles of the drone (fig. 29 B) being less isolated. On each 

 side of the tergum of segment V two bands of muscle fibers diverge 

 posteriorly to attach on the antecosta (Ac) of tergum VI. These 

 muscles are the internal dorsals, one median (133), the other lateral 

 (136). The single short external dorsal (13/) is a reversed muscle, 

 since it arises posteriorly on tergum V and extends forward to its 

 insertion on the anterior apodeme (a) of tergum VI. The spiracular 

 muscles include a small occlusor (not seen in the figure) attached 

 at both ends on the spiracle itself, as shown in segment VII (C, 180), 

 and a long, slender dilator (A, 759) arising on the lateral apodeme 

 of the sternum (c). Of the three tergosternal lateral muscles, the 

 first {160) is a reversed muscle arising ventrally on the lower part 

 of the tergum and inserted dorsally on the long lateral apodeme of 

 the sternum (fig. 26 D, 14P). The other two lateral muscles cross 

 each other obliquely in the female (fig. 28 A) from the tergum to the 

 sternum, the one which is external {161) being attached on the sternal 

 margin, the other (i6^) on the posterolateral upper surface of the 

 sternum. In the male (figs. 26 E, 29 B) the second and third 

 lateral muscles are parallel. The external muscle is a broad band of 

 fibers (fig. 26 E, 130) attached on the sternal margin; the internal 

 lateral muscle includes two distinct groups of fibers {131a, 131b), the 

 second distinguished by its pale, whitish color, both attached on the 

 upper surface of the posterior part of the sternum. The sternal 

 musculature duplicates the pattern of the tergal musculature, there 

 being a pair of posteriorly divergent internal ventrals on each side 

 (fig. 28 A, B, i6j, 164), and a single reversed external ventral (A, 

 163) between the overlapping parts of the consecutive sterna. 



Functionally the internal dorsal and ventral muscles are contractors 

 of the abdomen, inasmuch as they retract the individual tergal and 

 sternal plates. The external dorsal and ventral muscles of the more 

 posterior segments, on the other hand, are extensors of the abdomen, 

 since their contraction protracts the segmental plates by reducing the 

 overlap between them. Similarly, the reversed muscles of the lateral 

 series are dilators of the abdomen (fig. 26 D, 149), because their 

 contraction separates the tergum and the sternum of each segment. 



