68:19 But, as a high priest of the Melchizedek Priesthood has authority to officiate in all the lesser offices he may officiate in the office of bishop when no literal descendant of Aaron can be found, provided he is called and set apart and ordained unto this power, under the hands of the First Presidency of the Melchizedek Priesthood.

 68:20 And a literal descendant of Aaron, also, must be designated by this Presidency, and found worthy, and anointed, and ordained under the hands of this Presidency, otherwise they are not legally authorized to officiate in their priesthood.

 68:21 But, by virtue of the decree concerning their right of the priesthood descending from father to son, they may claim their anointing if at any time they can prove their lineage, or do ascertain it by revelation from the Lord under the hands of the above named Presidency.