From the performance notes:

Each player selects a single melody [from 26 melodies] to play at the start of the performance without consulting the other players, if any. The piece begins when the first player begins his melody. The remaining players, if any, must begin their melodies within the duration of one of the other players’; that is to say, any single player may not wait until all other performers have completed their melodies to begin his own. Each player must perform his complete melody within the exact duration specified at the end of each staff. Timekeeping devices must be used. Each player will mark the beginning of his time with the start of his first note. Individual notes may be held for any duration less than the duration of the entire melody and pauses may be added between the individual pitches, although not before the first and after the last notes of each melody. The choice of dynamics, articulations, extended techniques, and the clef in which a melody is played is left to the performer.

The premiere performance of Melodies featured five flutes.