64 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



The extension of the flexed wings preparatory to flight is in general 

 produced by the basalar sclerites and their muscles. In a dead speci- 

 men a sHght pressure on the basalare of either wing, or a pull on its 

 muscle, brings the wing out at right angles to the body and d'eflects 

 its anterior margin. The fore wing of the bee, however, is provided 

 with a small pleuroalar muscle (fig, 19 C, ^4), which arises on the 

 anterior marginal carina of the mesopleuron (fig. 17 C, ^4) just 

 below the attachment of the spiracular muscle (/j), and extends 

 dorsally and posteriorly to its insertion by two branches attached 

 ventrally on the humeral complex of the wing base (fig. 19 C). This 

 muscle evidently must be an accessory wing-extensor. In some insects 

 a depression of the second axillary, produced by the pull of the subalar 

 muscle, helps to extend the wing, but an extensor action of the second 

 axillary cannot be demonstrated in the bee. 



V. THE LEGS 



The legs of Hymenoptera have the usual six segments of an insect 

 leg, namely a coxa, a trochanter, a femur, a tibia, a tarsus, and a 

 pretarsiis. A leg segment is to be defined as a section of the limb 

 independently movable by muscles attached on its base, except where 

 there is evidence of the union of segments or a suppression of muscles. 

 The tarsus is usually divided into subsegments, or tarsomeres, which, 

 though movable on each other, are not "tarsal segments" since only 

 the proximal piece is provided with muscles. The flexible areas be- 

 tween segments or subsegments are the joints of the leg. The 

 proximal tarsomere, especially when differentiated by size or other 

 features, as in the bee, is designated the hasitarsus. The pretarsus 

 either terminates in a single claw, or dactyl, or it bears a pair of 

 lateral claws, or ungues, and usually a median lobe, the arolium. 



The three pairs of legs of the bee are attached at somewhat different 

 angles on the thorax so that in their action they are radially distributed 

 at the sides of the body. The coxae of the fore legs hang downward 

 on transverse axes of movement (fig. 11 G, Cx), and hence the 

 first legs swing forward and backward in the transverse planes of the 

 coxae. The middle coxae are transversely elongate and set obliquely 

 into the under wall of the thorax (figs. 15, 16 F), and the trochanters 

 are attached at their mesal ends; the middle legs, therefore, are 

 limited in their up-and-down motion, and swing forward and back- 

 ward by the revolution of the coxae on the body. The hind coxae 

 also have obliquely transverse axes on the thorax (figs. 15, 16 F), 

 but they are directed posteriorly and hence give the hind legs a more 



