Mass. Gen. Laws ch. 158, § 7

The subscribers to the agreement of association shall hold the franchise until the organization has been completed; and, unless it is otherwise provided in such agreement, each subscriber who elects to take such shares at the first meeting may take such proportion of the shares of the capital stock as the number of subscribers to the agreement bears to the whole number of shares, or any part of such proportion, upon paying the assessments thereon as called for by the corporation. All shares not so taken shall be disposed of as the corporation determines.