FLIGHT OF INSECTS. 345 



sooner is the insect emancipated from its con- 

 finement, 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. Their moisture rapidly evaporates, leav- 

 ing the delicate film dry and firm, so as to be 

 ready for immediate action. The fibres, or 

 nervures, as they are called, form a delicate 

 net- work, for the support of this fine membrane, 

 like the frame of the arms of a windmill, which 

 supports the canvass spread over them. The 

 microscope shows that these fibres are tubular, 

 and contain air ; a structure the most effectual 

 for conjoining lightriess with strength ; and many 

 entomologists are of opinion that the insect has 

 the power, during the act of flying, of directing 

 air into the nervures, so as to dilate them to the 

 utmost, and render them quite tense and rigid. 



In the great majority of insects the wings are 

 four in number ; of which the first pair are, as 

 we have seen, affixed to the mesothorax, and the 

 second to the metathorax. These two segments 

 of the thorax, composing what has been termed 

 the alitrunk, constitute the most solid portion of 

 the skeleton, and are frequently strengthened by 

 ridges, and other mechanical contrivances for 

 mpport. The superior extremities of these sup- 

 >orts, which have been compared to the clavicles, 



