II 



ANATOMY AND PHYSIOLOGY 



59 



B 



As the wing moves in the arc of a circle, the radius of which is the length 

 of the wing, the extreme tip of the wing records only a short mark; if, 

 however, the wing is pressed against the smoked cylinder, a large part 

 of the figure-8 trajectory may be obtained, as in Fig. 76, B. The wings 

 of the two sides move synchronously, as Marey found. 



The smaller the wings are, the more rapidly they vibrate. Thus a 

 butterfly (P. rapce) makes 9 

 strokes per second, a dragon 

 fly 28, a sphingid moth 72, a 

 bee 190 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 diagrammatically in Fig. 

 77, B. Besides these, there 

 are certain muscles of flight 



which act indirectlv unon the PIG - 77 '~~ At dia s ram to illustrate the action 



B of the wing muscles of an insect. B, diagram of 

 WingS, by altering the form. Of wing muscles, a, alimentary canal; en, muscle 



the thoracic wall. Thus the 



for contracting the thorax, to depress the wings; 

 d, depressor of wing; e, elevator of wing; ex, 



to elevate the 



muscle ie (Fig. 77, B) elevates musc l e for expanding the thorax, t 



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



the Wing by pulling the tergum /, leg muscle; p, pivot, or fulcrum; 5, sternum; /. 

 toward the Sternum; and the tergum; ^, 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. 



