insects: wings and theie appendages. 



83 



by a series of hairs or spines running along the front 

 edge of the hind- wing ; they are bent up into strong 

 semicircular 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 shding of 

 the front over the hind 

 pair. 



The wings of many in- 

 sects are interesting on 

 account of the organs 

 with which they are 

 clothed. A familiar ex- 

 ample is furnished by 

 the common Gnat, a 

 wing 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- 

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

 numerous and minute. But along the nervures, and 

 along other lines which run (generally) parallel with 

 the front margin, and also along the whole margin, 

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

 pearance and structure. 



Confining our attention to one of these lines, sup- 

 pose one of the nervures, we see that its course is 



DOUBLING AND HOOKS IN A BEE 8 WING. 



