Their legs are very delicate--the
anterior ones very long--and their abdomen terminates in two or three
long articulated filaments. One character, which is unique among
insects, is peculiar to Ephemerids; the adults issuing from the pupal
envelope undergo still another moult in divesting themselves of a thin
pellicle that covers the body, wings, and other appendages. This is what
is called the _subimago_, and precedes the imago or perfect state of the
insect. The short life of adult May-flies is, with most of them, passed
in a continual state of agitation. They are seen rising vertically in
a straight line, their long fore-legs stretched out like antennae, and
serving to balance the posterior part of the body and the filaments
of the abdomen during flight. On reaching a certain height they allow
themselves to descend, stretching out while doing so their long wings
and tail, which then serve as a parachute. Then a rapid working of these
organs suddenly changes the direction of the motion, and they begin to
ascend again. Coupling takes place during these aerial dances. Soon
afterward the females approach the surface of the water and lay therein
their eggs, spreading them out the while with the caudal filaments, or
else depositing them all together in one mass that falls to the bottom.
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