The business of the association shall be managed by not fewer than seven members, who shall be styled a board of managers, shall be chosen annually by the stockholders and shall hold their offices until others are chosen and have qualified in their stead, except that when the bylaws of such association so prescribe, the board of managers may be divided into not more than three classes, each class to hold office for not more than three years, one of which classes shall be elected annually. Such association shall have such other officers appointed as its bylaws prescribe.