308 THE MECHANICAL FUNCTIONS. 



§ 9. Flight of Insects. 



If the excellence of a mechanic art were mea- 

 sured by the difficulties to be surmounted in the 

 attainment of its object, none surely would rank 

 higher than that which has accomplished the flight 

 of a living animal. No human skill has yet con- 

 trived the construction of an automaton, capable, 

 by the operation of an internal force, of sustaining 

 itself in the air, in opposition to gravity, for even a 

 ie\Y minutes ; and far less of performing in that ele- 

 ment the evolutions which we daily witness even in 

 the lowest of the insect tribes. To the ultimate 

 attainment of this faculty it would appear that all 

 the transformations they undergo in external appear- 

 ance, and all the developements of their internal 

 mechanism, are expressly directed. Wings are 

 added to the frame only in the last stage of its com- 

 pletion ; after it has disencumbered itself of every 

 ponderous material that could be spared, after it 

 has been condensed into a small compass, and after 

 it has been perforated in all directions by air-tubes, 

 giving lightness and buoyancy to every part. Cu- 

 riously folded up in the pupa, the wings there 

 attain their full dimensions, ready to expand when- 

 ever the bandages which surround them are re- 

 moved. No sooner is the insect emancipated from 

 its confinement, than these organs, which are com- 

 posed of duplicatures of a dense, but exceedingly 

 fine membrane, identical in its composition with 

 the general integuments, begin to separate from the 

 sides of the body, and to unfold all their parts. 



