MECHANISM OF THE WING 



157 



space between the base or pedicel of the wing and the aperture in the thorax is 

 lined with a thin yielding membrane, on which the wing is suspended as on an 

 axle-tree. According to this, therefore, the insect wing, as well as any other 

 appendage of arthropods, 

 acts as a lever with two 

 arms. The reader can then 

 conjecture what may be the 

 further mechanism of the 

 wing machine. We only 

 need, now two muscles dia- 

 metrically opposed to each 

 other and seizing on the 

 power arm of the wing, one 

 of which pulls down the 

 short wing arm, thereby rais- 

 ing the oar, while the other 

 pulls up the power arm. 

 And indeed the raising of 



Fin. 172. Scheme of the flying apparatus of an insect: 

 mnl, thoracic walls ; ab, wings ; c, pivot ; d, point of insertion 

 of the depressor muscle of the wing (ted); a, that of the ele- 

 vator of the wing (ai) ; , muscle for expanding, ml, for 

 contracting, the walls of the thorax. After Graber. 



the wing follows in the man- 

 ner indicated, since a muscle 

 (hi) is attached to the end of the wing-handle (a) which projects freely into 

 the breast cavity by the contraction of which the power arm is drawn down. 

 On the other hand, we have been entirely mistaken in reference to the 



mechanism which lowers the wings. The muscle 

 concerned, that is M, is not at all the antagonist 



s ch- 



ef the elevator muscle of the wing, since it is placed 



close by this latter, but nearer to the thoracic wall. 

 But then, how does it come to be the counterpart of 

 its neighbor ? In fact, the lever of the wing is situated 

 in the projecting piece alone. The extensor muscle 

 of the wing does not pull on the power arm, but on 

 the resistant arm on the other side of the fulcrum (c). 

 The illustration shows, however, how such a case is 

 possible. The membrane of the joint fastening the 

 wing-stalk to the thorax is turned up outwards below 

 the stalk like a pouch. The tendon of the flexor of 

 the wing passes through this pouch to its point of 

 attachment (c) lying on the other side of the fulcrum 

 (d). Thus it is very simply explained how two 

 muscles which act in the same direction can never- 

 theless have an entirely contrary working power. 



This is in a way the bare physical scheme of the 

 flying machine by the help of which we shall more 

 easily become acquainted with its further details. 



Dragon-flies are unquestionably the most suitable 



FIG. 173 Muscles of the objects for the study of the muscles pulling directly 

 fore wing of a dragon-fly (an, J * 



ax), exposed by removing the on the wing itself. If the lateral thoracic wall (Fig. 



thoracic walls: A t , // eleva- jys) b e rem oved or the thorax opened lengthwise 



tors, SI-SB, depressors, of the 



wings (* * 2 , rotators). After there appears a whole storehouse of muscular cords 



Graber - which are spread out in an oblique direction between 



the base of the wing and the side of the thoracic plate. There is first to be 

 ascertained, by the experiment of pulling the individual muscles in the line 

 with a pincers, which ones serve for the lifting and which for the lowering 



