62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



triangular area of the dorsal part of the notum. A downward pres- 

 sure on this region of the metanotum at once turns the hind wings 

 upward, leaving little doubt that the metanotal muscles are wing 

 elevators. 



The horizontal and rotary components of the wing motion, by which 

 the wings are turned forward with the costal margins deflected during 

 the downstroke, and reversed during the upstroke, are produced 

 chiefly by the muscles of the basalar and subalar sclerites. It is these 

 movements that convert the wings from mere flaps into organs of 

 propulsion. The mechanism involved is equally developed in each 

 wing-bearing segment of the bee. The epipleural sclerites, as already 

 explained (figs. 19 B, I, 21 C, Ba, Sa), are hinged to the upper 

 edges of the pleura in such a manner that the contraction of their 

 muscles turns them mesally in the subalar membranes. The move- 

 ments of the sclerites are effective on specific points in the wing bases 

 because a tract of the membrane intervening between each sclerite 

 and the wing is so tightly stretched that it acts as a direct union, and 

 often gives a superficial appearance of being a connecting ligament. 

 The basalare in each wing of the bee is thus connected with the 

 humeral complex of the wing base, and the subalare with the posterior 

 lever arm of the second axillary (fig. 21 B). Contraction of the 

 basalar muscle during the downstroke of the wing, therefore, revolves 

 the basalare inward on its pleural hinge, and the tension exerted on 

 the wing base turns the descending wing forward on the pivotal 

 second axillary and deflects its costal margin. Similarly, during the 

 upstroke, the subalar muscle acting on the subalare pulls on the lever 

 arm of the second axillary and thus tilts the wing downward pos- 

 teriorly, so that the costal margin turns upward and moves backward, 

 relative to the body, while the wing is ascending. 



Flexion and extension of the zvings. — When the bee alights after 

 flight, or when the organs of flight are not otherwise in use, as in 

 "fanning," the wings are flexed posteriorly, the hooks on the hind 

 wings automatically loosing their grasp on the fore wings, and both 

 pairs of wings are laid over the back, the fore wings on top of the 

 hind wings. The mechanical problem involved in the horizontal flexing 

 of an insect's wing may be illustrated with a piece of paper firmly 

 held flat at one end and bent horizontally on itself ; the bending 

 necessarily produces a fold across the base. Conversely, if the paper 

 is folded in the same way, it automatically bends backward at a right 

 angle to its flat position. The flexing apparatus of the wing acts on 

 the second principle — by the production of a basal fold the wing is 

 turned horizontally backward. The fold-producing mechanism is the 



