Three at least out of his seven extant plays are written for performance by two actors only.[674] This limitation upon the number of the performers necessitated great simplicity in the construction of the play, since it was impossible for more than two personages to take part in the dialogue at the same time. Hence the earlier plays of Aeschylus, though essentially dramatic in comparison with anything which preceded them, are simple in plot and lyrical in tone when compared with the tragedies of his successors. The different scenes rather serve to unfold a series of pictures than to develop a complicated plot. Descriptive speeches take the place of animated dialogue. Sophocles added greatly to the capacities of the drama by introducing a third actor.[675] He was thus enabled to give much greater variety and spirit to the dialogue. In his hands for the first time tragedy became completely dramatic, and the lyrical element was thrust still further into the background. The innovation of Sophocles was adopted by Aeschylus in his later years, and the Orestean trilogy—the last and most elaborate of his works—requires three actors. Under Sophocles tragedy received its full development. The number of actors in tragedy was henceforward limited to three. The satyric drama was intimately connected with tragedy, and the number of actors was apparently the same. Thus the Cyclops of Euripides, the only extant satyric play, requires three actors. In the Naples vase-painting, which represents the performers in a satyric play, three actors are depicted.[676] It is true that the Alcestis of Euripides, which was performed in place of the usual satyric drama, only requires two actors. But the number in this case was probably due to the choice of the poet, and not to any official regulation. In regard to comedy, very little is known as to the steps by which it was developed. The source of comedy lay in the phallic songs performed at the festivals of Dionysus. The dramatic element originated in the interludes by the leader of the chorus. The process of development must have been much the same as in tragedy; but the names of the persons who introduced actors and dialogue into comedy were forgotten even in Aristotle’s time. The only piece of information upon the subject is to the effect that Cratinus was the first to limit the number of actors to three, and that before his time there was no regulation as to the number of persons introduced upon the stage. After the time of Cratinus there were no further innovations, and the number of the actors in comedy was permanently fixed at three.[677]