ing it. Nevertheless, she made the same mistake with the nail
shortly after. I have often made similar observations. We may certainly
conclude that the wasp saw something of the size of a fly, but without
distinguishing the details; therefore she saw it indistinctly. Evidently
a wasp does not only perceive motion; she also distinguishes the size of
objects. When I put dead flies on a table to be carried off by another
wasp, she took them, one after another, as well as spiders and other
insects of but little different size placed by their side. On the other
hand, she took no notice of insects much larger or much smaller put
among the flies.

Most entomologists have observed with what ingenuity and sureness
dragon-flies distinguish, follow, and catch the smallest insects on the
wing. Of all insects, they have the best sight. Their enormous convex
eyes have the greatest number of facets. Their number has been estimated
at 12,000, and even at 17,000. Their aerial chases resemble those of the
swallows. By trying to catch them at the edge of a large pond, one can
easily convince oneself that the dragon-flies amuse themselves by making
sport of the hunter; they will always allow one to approach just near
enough to miss catching them. It can be seen to what degree they are
able to measure the distance and reach of their enemy.

It is an absolute fact that dragon-flies, unless it is cold or in the
evening, always manage to fly at just that distance at which the student
cannot touch them; and they see perfectly well whether one is armed with
a net or has nothing but his hands; one might even say that they measure
the length of the handle of the net, for the possession of a long handle
is no advantage. They fly just out of reach of one's instrument,
whatever trouble one may give oneself by hiding it from them and
suddenly lunging as they fly off. Whoever watches butterflies and flies
will soon see that these insects also can measure the distance of such
objects as are not far from them. The males and females of bees and ants
distinguish one another on the wing. It is rare for an individual to
lose sight of the swarm or to miss what it pursues flying. It has been
proved that the sense of smell has nothing to do with this matter. Thus
insects, though without any power of accommodation for light or
distance, are able to perceive objects at different distances.

It is known that many insects will blindly fly and dash against a lamp