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MR. n. B. A. MALLOCK ON 



more complex. The muscles are never directly attached to the 

 wings, but to various portions of the thorax, quite distant from 

 the wing-joint, and deformation of the thorax caused by their 

 contraction acts indirectly on the wings. It would require more 

 elaborate figures than can be given here to make this action 

 clear, but text-figs. 4, 5, and 6 indicate roughly the sections (in 

 the three principal planes) of the thorax and groups of muscles. 

 The dotted lines in 5 and 6 show the kind of deformation 

 produced by the more or less horizontal and vertical groups. 



The question arises as to why has this complicated and indirect 

 method prevailed. 



Text-fie'ure 3. 



Diagrammatic half cross-section. 

 Action of winp-.muscles of Dragon-flies. 



If tlie pi'oblem were set of designing a mechanism for flapping 

 wings the dragon-flies solution would certainly be the first to 

 suggest itself ; yet it evidently must have some disadvantages 

 since it has not been generally adopted. 



Amongst many other curious mechanical devices found in 

 insects the folding of the wings is worth attention. The folding 

 here referred to is not the mere alteration of the attitude of the 

 wings at rest and in flight ; but an actual folding of the wing 

 itself, after the manner of a fan. Here, again, more elaborate 

 figures than ca,n be given in this place would be required to show 

 the complexity which is found in some of these folded wings. 



The simplest is that used by some of the Hymenoptera, where 

 a, single longitudinal fold is formed from the base to near the tip. 

 This, while not altering the length of the wing in repose, 

 diminishes its width. In the majority of flying beetles the length 

 of the wing in the folded position is reduced. This is effected by 

 a joint on the leading edge of the wing from which the nervm-es 

 on the folding part of the wing-membrane radiate. The wing so 



