32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



A discussion of the working mechanism of the sucking pump with- 

 out observations on the action of the organ in a living bee could be 

 but little convincing, and will not be attempted here, except to point 

 out that the cibarial section, with its strong equipment of dilator and 

 compressor muscles, must be the active pumping apparatus, or true 

 suctoriiun. With the bee, however, an important function of the feed- 

 ing mechanism is regurgitation. It is probable, therefore, that the 

 pump is capable of reversing its action according as the occasion 

 demands an intake or an output of food material. 



II. THE PROTHORAX 



The prothorax of the bee, as of most other clistogastrous Hymenop- 

 tera, is not an anatomical unit because of the close association of 

 the pronotum with the pterothorax, and the independence of the 

 prothoracic pleurosternal complex, or propectus, which serves as a 

 suspensorium for the first legs and as a support for the head. 



The pronotum. — The notal plate of the prothorax is a collarlike 

 sclerite closely fitted on the anterior end of the mesothorax (fig. 15, 

 A^i). Since its tapering lower ends meet on the venter, though they 

 do not unite (fig. 11 A), the pronotum forms a sclerotic annulus inter- 

 polated between the pleurosternal parts of its own segment and the 

 mesothorax. The lateral areas of the pronotum are produced pos- 

 teriorly into a pair of spiracular lobes {spl) that cover depressions 

 of the mesothorax and conceal the first spiracles on their inner 

 surfaces. The posterior pronotal margin dorsally is sharply and 

 deeply inflected with the anterior margin of the mesonotum (fig. 

 II F) ; from the latter depends a small prephragma (iPh), but the 

 pronotum is separated from the base of the phragma by a narrow 

 line of intersegmental membrane (Mb). 



The propectus. — The pleurosternal region of the prothorax is 

 merged with the neck in a prenotal cone (fig. 15), which is partly 

 overlapped posteriorly by the pronotum and tapers forward to its 

 connection with the foramen magnum on the back of the head. The 

 dorsal wall of the cone is the dorsal neck membrane, which is un- 

 interrupted from the head to the pronotum ; the lateral and ventral 

 walls contain the pleural and sternal plates of the prothorax, which 

 together constitute the propectus (fig. 11 G). 



Each prothoracic pleuron is an elongate triangular plate (fig. 11 C), 

 the anterior apical part of which tapers into a mesally bent occipital 

 process (C, E, e) that articulates with the corresponding occipital 

 condyle of the head (B), and which, therefore, would appear to 



