\\ \K.\I\ v\n I'll 



B 



As the wiu^ tnOVefl iii the .in <>i | . in Ic, th 



of the \vm.u, the extreme tip of the wintf i 



however, the winj is preed a.^im-t tin- -moked , ylindrr. ;i lar<_" 



of the figure S 1r;ije< tnry may he obt ailie< I . U ill Fitf. /'). /I. I 



.f the tWO Bidca move synchronously, a> Maivy found. 



The smaller the win^s are, the more rapidly they vibrate. Th 

 butterfly (/'. mine) makes 9 

 stroke^ per .second, a dragon 

 tly j8, a sphingid moth 72, a 

 bee i go and a house fly 330. 



Wing Muscles. The base 

 of a wing projects into the 

 thoracic cavity and serves for 

 the insertion of the direct 

 muscles of flight. Regarding 

 the wing as a lever (Fig. 77, 

 A) with the fulcrum at p, it 

 is easy to understand how the 

 contraction of muscle e raises 

 the wing and that of muscle d 

 lowers it. These muscles are 

 shown cliagrammatically in Fig. 

 77, B. Besides these, there 

 are certain muscles of flight 



which art indirertlv nnon the PlG - 77-~ A diagram to illustrate the action 

 ,tly Upo B Qf the wing musdes of an insect B diagram of 



wings, by altering the form of wing muscles, a, alimentary canal; en, muscle 



,1 . , , rrii A i for contracting the thorax, to depress the wings; 



the thoracic Wall. Thus the dt depressor of wing; e. elevator of wing; ex. 



muscle ie (Fig. 77, B) elevates muscle for expanding the thorax, to elevate the 



wings; id, indirect depressor; ie, indirect elevator; 



the Wing by pulling the tergum /, leg muscle; p, pivot, or fulcrum; s, sternum; /. 



toward the Sternum; and the tergum; Wg . wing.-After GRABER. 



longitudinal muscle id depresses the wing indirectly by arching the ter- 

 gum of the thorax. 



Though up and down movements are all that are necessary for the 

 simplest kind of insect flight, the process becomes complex in proportion 

 to the efficiency of the flight. Thus in dragon flies there are nine 

 muscles to each wing: five depressors, three elevators and one adductor. 

 The earlier accounts of the mechanics of flight by Marey and others 

 have been modified and improved upon by Stellwaag and by Ritter. 

 whose modern methods of investigation have added considerably to our 

 knowledge of the subject. These later authors have shown, particu- 

 larly, the parts played by the thoracic sclerites during flight. 



