INSECTS 



nervures are hollow, and are, during life, filled with 

 a subtile fluid, which is supplied from the vessels of 

 the body. They contain also ramifications of the ex- 

 quisite spiral air-vessels. 



In this wing of the bee all of these structures may 

 be seen to greater advantage. Unlike the fly, which 

 has but a single pair of wings, the bee has two pairs, 

 of which the fore pair is the larger and more horny, 

 the hinder pair seeming to be, as it were, cut out 

 of the hinder and inner side of the fore ones. The 

 two edges the hinder edge of the fore pair and the 

 front edge of the hind pair then correspond, but 

 it is necessary that, during flight, when the wings are 

 expanded, the two wings on each side should main- 

 tain 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 un- 

 locked at the pleasure of the animal; for the wings 

 during repose slide over one another. This con- 

 trivance is furnished by a series of hairs or spines 

 running along the front edge of the hindwing; 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 forewing is strengthened, 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 relaxed, there is 



