82 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



second segments of the abdomen. The modification allows the muscles 

 of the transposed first abdominal segment (B, d, v) to become effec- 

 tive motors of the free part of the abdomen. The aculeate Hymenop- 

 tera thereby acquire a much greater abdominal mobility for the use 

 of the ovipositor or sting or for mating activities than is possessed by 

 any other insects. 



The mechanism of the clistogastrous petiole is well illustrated in 

 the honey bee, though the petiole itself in the bee is relatively short. 

 Particular attention to the petiole as an important part of the or- 

 ganization of the bee was first given by Betts (1923), who fully 

 describes its structure and its principal muscles. The propodeum and 

 the first segment of the functional abdomen are joined by a mem- 

 branous conjunctiva (fig. 27 A, C), which permits freedom of move- 

 ment of the abdomen on the propodeum, but the two parts are hinged 

 dorsally by a pair of articular points (C, f, /). Between the articular 

 points on the dorsal surface of the petiole is a small elevation of the 

 conjunctival membrane {e) connecting anteriorly with a notch in 

 the end of the propodeum {t). Within this swelling of the con- 

 junctiva is a dorsal pocket of the anterior end of the petiole (D, F, G) 

 having a strongly sclerotic floor supporting a median ridge (D, F, r). 

 Ventrally (A, E) the conjunctiva is a wide membrane between the 

 weak sternal plate of the propodeum {IS) and the sternal plate of 

 the petiole (IIS). The muscles that move the abdomen as a whole 

 are attached dorsally, laterally, and ventrally on the narrowed end 

 of the petiole (G) ; they represent dorsal intersegmental muscles 

 between the primarily first and second abdominal segments (fig. 26 A, 



B, C, d), and ventral intersegmental muscles of the metathorax (B, 



C, v) that pass over the first abdominal sternum to attach on the 

 second. 



The petiole muscles of the honey bee include two pairs of dorsal 

 muscles and two pairs of ventral muscles, but on account of the 

 positions of their attachment on the petiole, one pair of the dorsal 

 muscles are levators of the abdomen, one pair of ventrals are de- 

 pressors, and the other two pairs evidently produce sidewise move- 

 ments. The levator muscles arise by broad, spreading bases on the 

 lateral walls of the propodeum (figs. 27 B, C, 28 A, 120), and are 

 inserted by strong tendons that converge to their attachments on the 

 posterior end of the ridge on the floor of the petiole pocket (fig. 27 D, 

 F, G). These muscles thus acquire a short leverage on the propodeal 

 fulcra (/). The depressors of the abdomen are a pair of long 

 ventral muscles arising on the metathoracic components of the ptero- 

 thoracic endosternum (fig. 27 E, 118), and inserted medially on the 



