Mass. Gen. Laws ch. 168 § 18
The clerk of a mutual bank and such members of the board of trustees as may be required to be elected under section 14 shall be elected at the annual meeting or at a special meeting of the corporators between meetings of the corporation. The president shall be elected by the trustees. If any such office becomes vacant during the year, the trustees may, except as otherwise provided in this chapter, fill the vacancy or approve a new officer until the next annual meeting.
The members of the board of investment, the treasurer, vice treasurer, assistant treasurers, vice presidents and such other officers as may be determined to be necessary, as provided in section 17, shall be elected by the trustees and shall hold office during their pleasure and the trustees may fill vacancies in such offices at any time.
All trustees and other officers shall be sworn and shall hold their several offices until others are elected and qualified in their stead. A record of such qualification shall be made and preserved with the records of such corporation. If a person elected as trustee or other officer of such corporation does not, within 45 days thereafter, take the oath of office, the office thereupon shall become vacant; provided, that such oath may be taken in person at any office of such corporation or may be taken in writing before a notary public or justice of the peace and transmitted to such corporation within said period.
Mass. Gen. Laws ch. 168, § 18