INSECTS: WINGS AND THEIR APPENDAGES 91 



expanded, the two wings on each side should maintain 

 this relative position, neither overlapping the other, but 

 together presenting one broad surface, wherewith to beat 

 the air. There must be, therefore, some contrivance for 

 locking together the two edges in question, which yet 

 shall be capable of being unlocked at the pleasure of the 

 animal; for the wings during repose slide over one an- 

 other. This contrivance is furnished 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 

 outward, looking, under a high power, like the hooks on 

 a butcher's stall. On the other hand, the margin of the 

 fore-wing is strengthened, and is turned over with a shal- 

 low 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 

 relaxed, there is no hinderance to the sliding of the front 

 over the hind pair. 



The wings of many insects are interesting on account 

 of the organs with which 

 they are clothed. A fa- 

 miliar example is fur- 

 nished by the common 



Gnat, a wing of which SCALES ON A GNAT'S WINO. 



is on the slide now before me. There is the same gen- 

 eral structure as before two clear elastic membranes 

 stretched over slender horny tubular nervures, and stud- 

 ded 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 

 (generally) parallel with the front margin, and also along 



