210 THE BODY- WALL AND MUSCLES [CH. 



Another peculiarity in which the Dragonfly differs from the 

 more highly specialized insects, and resembles the lower insects of 

 much less powerful flight, is the fact that fore and hind-wings are 

 completely independent. Each has exactly the same muscle- 

 supply, and each works entirely on its own. The fore-wings can 

 be destroyed without affecting the working of the hind, and 

 vice versa. A number of authors, chiefly in text-books, have 

 asserted that a strong ligament connects the bases of fore and 

 hind-wings together. The error seems to have arisen from a 

 misinterpretation of a well-known figure by Lendenfeld (see 

 Sharp, Camb. Nat. Hist., Vol. v, p. 416; Packard, Text-Book of 

 Entomology, p. 158) in which what appears to be the cut border 

 of the thorax looks like a ligament. In his original figure, 

 Lendenfeld left this piece unnamed. 



A third point of interest is the presence of only one true axillary 

 or wing- pivot in the Dragonfly. This acts as the principal fulcrum 



Pig. 91. Diagram to illustrate antagonism of two parallel muscles acting on wing 

 of Dragonfly, ax axillary ; dp depressor ; el elevator ; nt notum ; pi pleurum ; 

 w wing. Original. 



of the wing. An examination of the position of this fulcrum shews 

 us that it lies closer to the middle line than do the tendons of the 

 depressor muscles. The tendons of the latter are inserted at 

 a level external to it (i.e. further from the middle line). Those 

 of the elevators, on the other hand, are inserted at a level internal 

 to it (i.e. nearer the middle line). Thus the wing acts as a lever 

 of the first order (i.e. the fulcrum lies between the power and the 

 weight) for the elevators, but as a lever of the third order (i.e. the 

 power between the fulcrum and the weight) for the depressors. 

 By referring to fig. 91, we thus see plainly how two sets of muscles 



