NO. 2 HONEY BEE SNODGRASS 45 



latter into two parts (Epm, epm), and then turns downward close 

 to the posterior epimeral margin, and, along with the pleural sulcus, 

 finally becomes lost in the intersegmental groove. This recurrent 

 groove also forms a strong internal ridge (B, /), and it too has been 

 regarded as the pleural sulcus (see Snodgrass, 1925), but it has none 

 of the distinctive features of the latter. Duncan (1939) gives the 

 same interpretation of the pleural structure in Vespula as is given 

 here for Apis. The obliteration of the lower part of the mesepimeron 

 makes it appear that the middle coxa (fig. 15) has an intersegmental 

 pleural articulation, though its ventral articulation is with the 

 mesosternum (fig. 16 F). 



Anteriorly the mesopleuron presents a deep concavity (fig. 17 A, 

 c), which is covered by the spiracular lobe of the pronotum (fig. 15 

 spl) ; its dorsal margin forms a long elevation, on the anterior part of 

 which (fig. 17 A, d) articulates the basalar sclerite (fig. 19 B, Ba), 

 and on the posterior part {WP) the second axillary of the wing base 

 {2 Ax). Behind the wing process {WP) the descending margin of 

 the epimeron is inflected mesally in a wide plate (fig. 17 B, Epm') 

 supported on the ridge (/) of the recurrent suture. The inner edge 

 of this inflected plate carries an elongate sclerite (G, h), attached 

 posteriorly to the base of the postphragma (fig. 19 I), which supports 

 the small subalare {Sa). 



The inner surface of the mesopleuron presents an unusual structure 

 (fig. 17 B). From its anterior and upper margin, between the first 

 spiracle and the wing process, there is reflected posteriorly a large 

 plate {g), the lower part of which is bridged to both the pleural 

 ridge {PIR) and the recurrent ridge (/) by a strong arch. Between 

 this plate and the outer pleural wall is a flat pocket open above and 

 below the bridge (as indicated in the figure by an arrow), which 

 lodges one of the muscles of the third axillary sclerite of the wing 

 base (E, '/6a). Behind the upper part of the pocket is seen the in- 

 flected external plate of the epimeron (B, Epm') united with the re- 

 current ridge (/). The thick pleural ridge (PIR) ends posteriorly in 

 the small pleural apophysis {PI A). 



The metathoracic pleuron is a narrow, oblique plate on the side of the 

 pterothorax (fig. 15), extending from the wing base above to the hind 

 coxa below, between the mesopleuron and the propodeum. It is di- 

 vided by a groove into a larger upper part {Ph) and a smaller lower 

 part {ph), but the latter is continuous ventrally with the metasternum 

 (S^). The dorsal plate (fig. 21 C, Ph) supports on its upper margin 

 the basalare {Ba), the second axillary {2 Ax), and the small subalare 

 {Sa) of the metathorax; it includes, therefore, in its upper part at 



