NO. 8 INSECT ABDOMEN SNODGRASS II5 



to inflict a wound. In many other Hymenoptera, however, the 

 alkahne gland is much larger than in the honey bee, and in general it 

 appears that this gland is best developed in the solitary bees. 



General structure of the abdomen. — In order to understand the 

 stinging mechanism of the bee it will be necessary to know something 

 of the structure and musculature of the entire abdomen, since the 

 movements of the abdomen as a whole are important in the act of 

 stinging. The abdomen is divided at the petiole between the first and 

 second segments (fig. 38 D). The first segment is the propodeum; 

 the rest of the abdomen is called the postahdomen. The propodeum, 

 however, is virtually a part of the thorax, and it is often convenient 

 to refer to the body section beyond it as the " abdomen ", though the 

 segments should be enumerated beginning with the propodeum. In 

 the act of stinging, the bee not only moves the postahdomen as a 

 whole on the propodeum, but it bends the distal segments of the 

 former abruptly downward and protrudes the sting often in an ap- 

 proxim.ately vertical direction. The general abdominal musculature 

 of the bee has been described by Betts (1923) and by Morison 

 (1927). 



The petiolate structure of the abdomen, which brings the point of 

 flexibility at the base between the first and second segments, gives a 

 much freer movement to the abdomen than is possible in the more 

 usual condition in which the play is between the metathorax and the 

 first abdominal segment, because it allows the muscles between the 

 first and second segments to be the efifectors. With insects having 

 the second pair of wings well developed, the dorsal muscles of the 

 metathorax are a part of the wing mechanism ; but in the higher 

 Hymenoptera the hind wings and the metathorax are both greatly 

 reduced, and the metathoracic muscles are in consequence so small 

 and so cramped for space that they could have little efifectiveness in 

 giving movement to the abdomen. In the bees, the second phragma 

 of the thorax extends backward through the metathorax into the 

 posterior part of the propodeum (fig. 38 A, 2Ph). A pair of muscles 

 (ds) arise in lateral concavities on the posterior surface of the 

 phragma and converge posteriorly and medially to a small median 

 apodemal process of the dorsal wall of the propodeum just above the 

 petiole (fig. 39, ds). These muscles are evidently the longitudinal 

 dorsals of the metathorax, the posterior ends of which have migrated 

 far backward on the tergum of the propodeum. 



The propodeum of the honey bee (fig. 38 D, /) consists mostly 

 of a large, strongly convex tergal plate (T) solidly incorporated 

 into the thorax by a complete fusion with the upper edges of the 



