CREATE TABLE table_72729 ("Series #" FLOAT, "Season #" FLOAT, "Title" TEXT, "Directed by:" TEXT, "Written by:" TEXT, "Original air date" TEXT)

Who directed the episode that was written by Jackson Gillis and Originally aired on May 21, 1955?
SELECT "Directed by:" FROM table_72729 WHERE "Written by:" = 'Jackson Gillis' AND "Original air date" = 'May 21, 1955'
SELECT "Directed by:" FROM "table_72729" WHERE "Original air date" = 'May 21, 1955' AND "Written by:" = 'Jackson Gillis'