INSECTS : "WINGS AND THEIR APPENDAGES. 



83 



by a scries of liairs or s})ines running along the front 

 edge of the liind-wing ; they are bent np into strong 

 seniicircular hooks, arching outwards, looking, under a 

 high power, like the hooks on a butcher's stall. On 

 the other hand, the margin of the fore-wing is strength- 

 ened, and is turned over with a shallow doubling, so 

 as to make a groove into which the hooks catch ; and 

 thus, while the fore-wings are expanded, the hooks of 

 the other pair are firmly locked in their doubled edge, 

 while, as soon as flight ceases, and the wings are re- 

 laxed, there is no hin- 



drance to the sliding of 

 the front over the hind 

 pair. 



The wings of many in- 

 sects are interestino- on 

 account of the organs 

 with which they arc 

 clothed. A familiar ex- 

 ample is furnished by 

 the common Gnat, a 

 M'iiig of which is on the slide now before me. There 

 is the same general structure as before, — two clear elas- 

 tic membranes stretched over slender horny tubular 

 nervures, and studded on both surfaces with short spine- 

 like hairs, which in this case, however, are excessively 

 numerous and minute. But along the nervures, and 

 along other lines which run (generallj^) parallel with 

 the front marfjin, and also alono' the whole marmn, 

 there are set long leaf-like scales of very curious ap- 

 pearance and structure. 



Confining our attention to one of these lines, sup- 

 l)ose one of the nervures, we see that its course is 



DOUBLING AND HOOKS IN A BEE S 'WIXG. 



