66 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



lation, and the ligamentous connection (fig. 30 A, b) between the 

 subalare (Sa) and the second axillary (2Ax) gives this muscle a 

 functional relation to the median or posterior part of the wing base. 

 The muscle of the third axillary (figs. 28, 30 A, D), often with 

 several branches, arises from the pleural ridge or from neighboring 

 parts of the pleuron, and goes obliquely dorsally and posteriorly to 

 its insertion on the muscle process of the third axillary (3 Ax). In 

 the Diptera there are two small muscles inserted on the first axillary, 

 and in many insects there are various other small muscles associated 

 with the wing base, but all of these muscles are of secondary im- 

 portance and probably of a secondary origin. 



It is difficult to demonstrate the action of the wing mechanism 

 in a dead insect, but, allowing for much greater efficiency of the 

 apparatus under the tension of living muscles, a pretty fair under- 

 standing of the various wing motions may be obtained from a study 

 of freshly killed specimens. Take some large Diptera, for example 

 (Syrphidae, Muscoids). The wings of the dead fly are usually flexed. 

 A lengthwise compression of the back of the mesothorax partly ex- 

 tends the wings and gives to each a downward motion accompanied 

 by a strong deflection of the costal margin. A vertical compression 

 of the thorax elevates the wings, and most strongly the costal mar- 

 gins. If a piece is cut out of the middle of the tergum, the wings 

 no longer respond to pressure on the thorax in either direction, show- 

 ing that the movements of the tergum, though slight, are sufficient 

 to produce the wing motions. It is evident, too, that the nature of 

 the wing articulation produces, in part at least, the compound char- 

 acter of the wing movements, but these movements are greatly ac- 

 centuated by the action of other parts of the mechanism. The most 

 decisive movement in the wing results from a downward pressure 

 on the second axillary sclerite of the wing base, the wing being 

 immediately extended, while the hind margin turns downward until 

 the plane of the wing is almost vertical, with the costal margin upper- 

 most. Complete extension of the wing in a horizontal plane results 

 from pressure on the basalar plate or basalar lobe of the episternum. 

 The wing of the freshly killed insect can thus be made to perform 

 most of its movements by pressure on various parts of the thorax, 

 and an understanding of the wing mechanism then becomes a matter 

 of determining what muscles may produce the movements observed. 

 Since the Odonata, the Ephemerida, and the Palseodictyoptera do 

 not flex the wings, the apparatus of elevation and depression by 

 means of the indirect wing muscles was undoubtedly the first part 



