FLIGHT OF INSECTS. 247 



pie extent, forming, when expanded, a quadrant of a circle, 

 with five or six nervurcs radiating from their base, and 

 folded longitudinally. 



In the Hetniptera, the tegmina, or as they are here 

 called, the hemi-elytra^ are coriaceous towards their base, 

 but membraneous towards their extremity, and the true 

 wings are folded transversely, so as to cross one another. 

 These hemi-elytra are employed to strike the air in flight, 

 and their movements accompany those of the wings. 



Insects having four thin membranous and transparent 

 wings are arranged under two orders; namely, the Neurop- 

 tera (Fig. 160,) in which the lesser nervures form an inter- 

 lacement of fibres, crossing one another nearly at right 

 angles, like net-work, or lace: and the Hymenoptcra (Fig. 

 161,) in which they are disposed like the ramifications of 

 arteries or veins, diverging at acute angles from the main 

 trunks. The insects belonging to these two orders enjoy 

 extensive powers of flight. Libellulse, and JEschnse^ which 

 are included in the first of these orders, never close their 

 wings, but, when they are not flying, keep them constantly 

 expanded, and ready for instant action. They fly with the 

 greatest ease in all directions, sideways, or backwards, as 

 well as forwards, and can instantly change their course with- 

 out being obliged to turn their bodies. Hence they possess 

 great advantages both in chasing other insects, and in evading 

 the pursuit of birds. Bees^ which are hymenopterous in- 

 sects, have often been observed to fly to great distances 

 from their hive in search of food. The humble bee adopts 

 a very peculiar mode of flight, describing, in its aerial course, 

 segments of circles, alternately to the right and to the left. 

 The velocity with which these insects move through the 

 air, in general, much exceeds that of a bird, if estimated with 

 reference to the comparative size of these animals.* 



* I have been favoured by Mr. George Newport with the following ac- 

 count of the structure of the sting of the Wild Bee, {Anthophora rctusOy 

 Kirby) which he has lately carefully examined, and from whose drawings 

 of the dissected parts the annexed figures (163) have been engraved, " The 

 sting of the bee, a, is formed of two portions placed laterally together, but 



