the former being probably the opening speech recited
by the _coryphaeus_, the latter the dialogue between him and the actor.
It was a natural result of the introduction of the second actor that a
second _rhesis_ should likewise be added; and this tripartite division
would be the earliest form of the _trilogy_,--three sections of the same
myth forming the beginning, middle and end of a single drama, marked off
from one another by the choral songs. From this Aeschylus proceeded to
the treatment of these several portions of a myth in three separate
plays, connected together by their subject and by being performed in
sequence on a single occasion. This is the _Aeschylean trilogy_, of
which we have only one extant example, the _Oresteia_--as to which
critics may differ whether Aeschylus adhered in it to his principle that
the strength should lie in the middle--in other words, that the
interest should centre in the second play. In any case, the symmetry of
the trilogy was destroyed by the practice of performing after it a
satyr-drama, probably as a rule, if not always, connected in subject
with the trilogy, which thus became a _tetralogy_, though this term,
unlike the other, seems to be a purely technical expression invented by
the learned.[66] Sophocles, a more conscious and probably a more
self-critical artist than Aeschylus, may be assumed from the first to
have elaborated his tragedies with greater care; and to this, as well as
to his innovation of the third actor, which materially added to the
fulness of the action, we may attribute his introduction of the custom
of contending for the prize with single plays. It does not follow that
he never produced connected trilogies, though we have no example of such
by him or any later author; on the other hand, there is no proof that
either he or any of his successors ever departed from the Aeschylean
rule of producing three tragedies, followed by a satyr-drama, on the
same day. This remained the third and last stage in the history of the
construction of Attic tragedy. The tendency of its action towards
complication was a natural progress, and is emphatically approved by
Aristotle. This complication, in which Euripides excelled, led to his
use of prologues, in which one of the characters opens the play by an
exposition of the circumstances under which its action begins. This
practice, though ridiculed by Aristophanes, was too convenient not to be
adopted by the successors of Euripide