34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I46 



the latter being necessary for directed flight. Both sets of move- 

 ments depend on a strong sup}X)rt of the wing on a pleural fulcrum. 



The vertical wing movements result from an alternating upward 

 curvature and flattening of the wing-bearing notum, the margins of 

 which thus depress or elevate the attached wings on the fulcral sup- 

 ports. The notal movements are produced by the antagonistic con- 

 traction of the dorsal longitudinal muscles and the notosternal verti- 

 cal muscles of the wing-bearing segments. But this action of the 

 muscles involved some radical alterations in the thoracic structure. 

 The dorsal muscles are intersegmental, and ordinarily serve to pull 

 the two tergal plates together, accompanied by an infolding of the 

 intersegmental membranes. To efifect a dorsal curvature of the 

 notum, therefore, the intersegmental membrane has to be replaced 

 by a sclerotization that would solidly unite the consecutive notal 

 plates. The sclerotized membrane forms the so-called postnotum of 

 the back. The tension produced by the muscles must now effect an 

 upward curvature of the notum, giving the downstroke of the wings. 

 The upstroke then follows from the depression of the notum by 

 the vertical notosternal muscles attached on it. With the develop- 

 ment of the wings the dorsal muscles became enormously increased 

 in size, and to accommodate them the notal ridges of their attach- 

 ments have been expanded into large plates, the intersegmental 

 phragmata of modern insects. 



The wing being a flat fold of the body wall, its upper layer is 

 continuous with the supporting notum, and its lower layer is reflected 

 into the pleural wall. The basal region of the wing is largely mem- 

 branous to allow for flexibility, but to maintain a hinge movement on 

 the notum small sclerites are present in the membrane that articulate 

 with specific wing processes of the notal margin. These sclerites, 

 though on the upper surface of the wing, are known as the axillaries. 

 A first axillary sclerite articulates with an anterior wing process of 

 the notum, a third axillary with a posterior notal process. An inter- 

 mediate second axillary loosely connects the other two and forms 

 ventrally the pivotal point of the wing on the pleural wing fulcrum. 



The mechanism that converts the flapping wing into an organ of 

 flight pertains to the pleuron. The under surface of the wing is con- 

 tinued into the pleuron by wide membranous areas before and behind 

 the pleural fulcrum. The wing, therefore, rocks freely on the ful- 

 crum. In the membranes before and behind the latter are small 

 sclerites, the hasalare and subalare respectively, on each of which 

 are attached vertical muscles. Since the sclerites are closely connected 



