56 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



distal end. In most insects the median plate is associated with the 

 bases of the veins media and cubitus, but in the Hymenoptera these 

 two veins appear to be combined, and united basally with the radius. 



The hind ■wing. — The small metathoracic wing of the bee (fig. i8 B) 

 has a more simplified venation than the fore wing, but it has the 

 same vein stems in its proximal part (fig. 21 A) except that there 

 are two veins {lA, 2 A) in the vannal region. The basal structure of 

 the hind wing also is simpler than that of the fore wing, and there is 

 no metathoracic tegula. The humeral complex supports only the first 

 two veins; a median plate and a fourth axillary are absent. 



The relatively small first axillary of the hind wing (fig. 21 A, B, 

 I Ax) articulates on the lateral plates of the metanotum (E), its 

 posterior process being received in a depression (/) of the lower 

 angle of the semi-detached plate (ws), its head resting on a small lobe 

 {e) of the free plate {d). Laterally the large head of the first 

 axillary abuts against the broad mesal end of the humeral complex 

 (A). The irregular second axillary (B, 2 Ax) lies laterad of the first 

 axillary (A) and articulates by a large ventral process in a notch on 

 the dorsal margin of the metapleuron (C). The third axillary is a 

 large, elongate sclerite (B, J^x) lying obliquely transverse behind 

 the second axillary (A) between the edge of the metanotum and the 

 base of the fourth wing vein. The large, fan-shaped, three-branched 

 muscle of the wing-flexing third axillary (B, F, G, H, 100) arises 

 on the anterior infold of the metapleuron (C, H, k) and is attached, 

 not directly on the third axillary, but on a minute sclerite of the wing 

 membrane (A, B, a) close to the base of the axillary, and hence 

 pulls indirectly on the latter through the intervening membrane. 



The epipleurites. — The epipleural sclerites associated with the under 

 sides of the wing bases include in each segment the hasalarc lying 

 before the pivotal second axillary, and the subalare lying behind it. 

 The sclerites are articulated on the upper edges of the pleura ; they 

 give insertion to muscles that deflect them inwardly and thus pull 

 on the wing bases by reason of the close membranous connection of 

 the epipleurites with the latter. The specific effect of the epipleurite 

 muscles on the wing movements will be described later. 



The basalare of the mesothorax (fig. 19 B, Ba) is an elongate 

 sclerite hinged by its entire length on a wide lobe {d) of the dorsal 

 margin of the mesopleuron, which supports posteriorly also the 

 second axillary {2 Ax). On the inner surface of the basalare is 

 attached by a strong apodemal tendon a large, fiat, fan-shaped muscle 

 (G, yy) arising on the anterior part of the pleuron (fig. 17 E), where 

 it partly overlaps internally the second and third muscles of the third 



