Once more recording for Victor (from 1940), with the small groups being issued on their Bluebird label, three-minute masterpieces on 78 rpm record sides continued to flow from Ellington, Billy Strayhorn, Ellington's son Mercer Ellington, and members of the orchestra. "Cotton Tail", "Main Stem", "Harlem Air Shaft", "Jack the Bear", and dozens of others date from this period. Strayhorn's "Take the "A" Train", a hit in 1941, became the band's theme, replacing "East St. Louis Toodle-Oo". Ellington and his associates wrote for an orchestra of distinctive voices who displayed tremendous creativity. Mary Lou Williams, working as a staff arranger, would briefly join Ellington a few years later.