Section 77. (a) Any laborer in the employ of a city or town, except Boston, which accepted chapter five hundred and three of the acts of nineteen hundred and twelve, who has been in such employ for not less than thirty-five years or who has reached the age of sixty and has been in such employ for not less than twenty-five years and who, in either case has become physically or mentally incapacitated for labor, and any laborer in the employ of such city or town who has been in such employ for not less than fifteen years and has become physically or mentally incapacitated for labor by reason of any injury received in the performance of his duties for such city or town may, at his request be retired from service by the appropriate retirement board, established under section twenty, or, if there is no such board in the case of a town, the selectmen; and if so retired he shall receive from the city or town for the remainder of his life an annual pension equal to one half of his annual rate of regular compensation for full time service as a laborer at his retirement. Any laborer in the employ of such city or town who has reached the age of sixty-five and has been in such employ for not less than twenty-five years, including the time when incapacitated by reason of sickness or other disability incurred in or arising out of the performance of his duty, not exceeding two years in the aggregate, as certified by a physician in regular standing, shall, at his request, be retired from service, and shall receive from the city or town an annual pension computed in the manner hereinbefore set forth. No laborer in the employ of such a city or town shall be eligible for retirement under any method provided in this section unless he has actually been employed by it as a laborer for at least thirty-two weeks in the aggregate in each of the years of employment required under such method, but this provision shall not affect the deduction of time permitted by the preceding sentence in the case of incapacity by reason of sickness or other disability.

(b) In any such city or town which accepts this paragraph prior to January first, nineteen hundred and forty-six, or has accepted this paragraph or corresponding provisions of earlier laws, ''laborers'' shall include foremen, inspectors, mechanics, draw tenders, assistant draw tenders and storekeepers, but the pension payable under this section to any person holding a position included as aforesaid within the meaning of the word ''laborers'' shall not exceed four hundred dollars a year, or, in any such city or town which after the effective date of chapter four hundred and fifty-eight of the acts of nineteen hundred and twenty-three accepted or shall accept this paragraph, whether or not it had accepted this paragraph or corresponding provisions of earlier laws prior to said date, five hundred dollars a year.

(c) In any city or town, except Boston, which accepted said chapter five hundred and three and shall accept this paragraph prior to January first, nineteen hundred and forty-six, whether or not it has accepted the preceding paragraph or corresponding provisions of earlier laws, ''laborers'' shall include foremen, inspectors, mechanics, draw tenders, assistant draw tenders and storekeepers, and the pension payable under this section to any person holding a position included as aforesaid within the meaning of the word ''laborers'' shall be computed in the manner set forth in paragraph (a).