MOTIONS OF INSECTS. 355 
sembling the fest 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 unfolding of 
these organs being necessary. In Agrion, the other 
genus of the tribe, the wings when they repose are not 
expanded. I have observed of these insects, and also 
of several others in different orders, that without turning 
they can fly in all directions—backwards, and to the 
right and left, as well as forwards. 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 menagerie about a hundred feet long. 
The little creature 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 distinguished, particularly in Ashna and Libellula, 
and such the force of the muscles that move them, that 
they seem never to be wearied with flying. I have ob- 
served one of the former genus (Anax Imperator, Leach) 
sailing for hours over a piece of water—sometimes to and 
fro, and sometimes wheeling from side to side; and all! 
the while chasing, capturing, and devouring the various 
insects that came athwart its course, or driving away its 
competitors—without ever seeming tired, or inclined to 
« Leeuw. Epist. 6. Mart. 1717. 
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