Remove all fat from duck including small glands at base of neck. Wash inside and out. Place neck, gizzard and heart in 4 cups water and cook slowly to make duck bouillon. Peel oranges and place peels inside duck and roast at 375 degrees for time as indicated by weight on package. (About 3 hours average.)
When duck is almost done add marmalade and vinegar to bouillon (you should remove neck and throw away). Add 3 tablespoons of cornstarch to water and make paste and then add to sauce. Allow to thicken then add the sections of the oranges. Do not overcook. Serve slices of duck topped with sauce.
