THE WINGS. 23 



serve to extend the delicate membrane^ and give it 

 sufficient firmness to act as an organ of flight ; they 

 are horny tubes, each of which appears to enclose a 

 vessel for the conveyance of fluid. They become 

 thicker and stronger towards the base of the wings, 

 where they furnish the points of attachment for the 

 muscles by which the necessary motions are given to 

 these organs for effecting the peculiar flight of the 

 insect. 



But although many insects are furnished with four 

 membranous wings, we find others in which there are 

 but two such organs, and these attached to the third 

 segment of the thorax, whilst the second segment 

 bears a pair of horny or leathery flaps very different 

 in appearance from an ordinary wing. Nevertheless 

 these are in reality the anterior pair of wings, in which 

 the integument has become horny or leathery, and on 

 examination they are found to consist, like true wings, 

 of two distinct plates united at their edges, and also 

 adhering to each other at various parts of their sur- 

 faces by means of slender columns of horny matter, 

 which have chambers of various forms between them. 

 These horny wings of course are not very serviceable 

 as organs of flight ; but to make up for this, the mem- 

 branous wings of the insects possessing them are of 

 very large size, and amply sufficient to bear their 

 owners through the air at a very respectable speed. 

 And we now see the object of the hardening of the 

 anterior wings, for the large membranous wings are 

 capable of folding themselves up into a small compass, 

 when they lie snugly packed upon the back of the 

 insect, and their firmer brethren then cover them up, 

 and protect them from all injury. From this office the 

 hard anterior mngs are called wing-cases or sheaths 



