156 



TEXT-BOOK OF ENTOMOLOGY 



of veins and a piece of india rubber the membrane spread out between them. 

 The reader will be patient while we just explain to him the act of unfolding of 

 the membranous wing of the beetle. The actual impulse for this unfolding is 

 due to the flexor muscles which pull on, and at the same time somewhat raise 



the vein on the costal edge. 

 By this means the mem- 

 branous fold lying directly 

 behind the costal vein is 

 first spread out. But since 

 this fold is connected with 

 the longitudinal fold of the 

 distal end of the wing which 

 closes like a blade, the 

 wing-area last mentioned 

 which is attached to the 

 middle fold of the wing by 

 the elastic spring-like diag- 

 onal vein becomes stretched 

 out. The hinder rayed por- 

 tion adjacent to the body 

 is, on the other hand, 

 simply drawn along when 

 the wing stands off from 

 the body. 



In order to properly 

 grasp the mechanism of 

 the insect wing we must 

 again examine its mode of 

 articulation to the body 

 somewhat more accurately. 

 If we select the halteres 

 of a garden gnat (Tipula) 

 at the moment of exten- 

 sion, we shall find them to 

 be formed almost exactly 

 after the pattern of our 

 oars, since the oblong oar- 

 blade passes into a longitu- 

 dinal handle. The pedicel 

 of the balancer is formed 

 by the thick longitudinal 

 primary veins of the wing- 

 membrane. This pedicel 

 (Fig. 171) is implanted in 

 the side of the thorax in 

 such a manner that the 

 wing may be compared to 

 the top of a ninepin. One 

 may think, and on the 

 whole it is actually the 

 fact, that the stiff pedicel of the wing is inserted in the thoracic wall, and that 

 a short portion of it (Fig. 172), projects into the cavity of the thorax. It is true 

 there is no actual hole to be found in the thoracic wall, as the intermediate 



