The twelve melodies of "Tierkreis" are character pieces, representing the twelve signs of the Zodiac. They are serial in conception and all are based on tone rows, though some have more than twelve notes—"Libra", for example, has fourteen, with F and D recurring in different octaves. Because music boxes preclude any significant variation in dynamics or timbre, the structure of the "Tierkreis" melodies emphasize pitch and rhythm. Each melody is centered on a different chromatic pitch, with "Leo" (Stockhausen's own sign) = A, Virgo = A, Libra = B, Scorpio = C, etc., and each has its own distinctive tempo, chosen from the "chromatic" tempo scale first described in the composer's famous article, "... How Time Passes ...".