MOTIONS OF INSECTS. 355 



ones. This doubtless renders it more difficult for the 

 birds to take them as they fly ; and thus the male, 

 when paired, often flits away with the female. 



Amongst the Neuropterous tribes the most conspi- 

 cuous insects are the dragon-flies (LibelluHdcE), which 

 — their metamorphosis, habits, mode of life, and charac- 

 ters considered — form a distinct natural order of them- 

 selves. Their four wings, which are nearly equal in 

 size, are a complete and beautiful piece of net-work, 

 resembling the finest lace, the meshes of which are 

 usually filled by a pure, transparent, glassy membrane. 

 In two of the genera belonging to this tribe, the wings, 

 when the animal is at rest, are always expanded, so 

 that they can take flight in an instant, no previous un- 

 folding of these organs being necessary. In Agrion, 

 the other genus of the tribe, the wings when they re- 

 pose are not expanded. I have observed of these in- 

 sects, and also of several others in different orders, 

 that Avithout turning they can fly in all directions — 

 backwards, and to the right and left, as well as for- 

 wards. This ability to fly all ways, without having to 

 turn, must be very useful to them when pursued by a 

 bird. Leeuwenhoek once saw a swallow chasing an 

 insect of this tribe, which he calls a Mordella^ in a me- 

 nagerie about a hundred feet long. The little crea- 

 ture flew with such astonishing velocity — to the right 

 — to the left — and in all directions — that this bird of 

 rapid wing and ready evolution was unable to overtake 

 and entrap it ; the insect eluding every attempt, and 

 being generally six feet before it*. Indeed, such is the 

 power of the long wings by which the dragon-flies are 



" Leeuw. Epist. 6. Mart. 1717. 

 2 A 2 



