Massachusetts Constitution Pt. 2, Ch. II, § 3, Art. 2

ART. II. [Nine councillors shall be annually chosen from among the persons returned for councillors and senators, on the last Wednesday in May, by the joint ballot of the senators and representatives assembled in one room: and in case there shall not be found upon the first choice, the whole number of nine persons who will accept a seat in the council, the deficiency shall be made up by the electors aforesaid from among the people at large; and the number of senators left shall constitute the senate for the year. The seats of the persons thus elected from the senate, and accepting the trust, shall be vacated in the senate.]