Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 63, § 21

Every foreign life insurance company shall annually pay with respect to business taxable under the preceding section, in addition to the excise hereby imposed, a sum equal to the excess over such excise of the amount of tax which would be imposed in the same year by the laws of the state or country under which such company is organized, upon a life insurance company incorporated in this commonwealth, or upon its agents, if doing business to the same extent in such state or country.