I say lead because after the exposition of each of the carol melodies in section A, it's always the English melody beginning the passage before the Polish melody follows two beat later. This happens in the beginning of section B, C, D and E. Even though there is change of the voices which is assigned the melodiees, I still think there can be some variations on the order of the appearence of the melodies, i.e. have the Polish Melody appears first and followed by the English melody!