Section 9. The mayor, city manager, or other executive head of a city and the city clerk, jointly and severally, shall have the duty of fulfilling all obligations imposed upon such city under this chapter. The board of selectmen, town manager, or other executive head of a town and the town clerk, jointly and severally, shall have the duty of fulfilling all obligations imposed upon such town under this chapter. Obligations imposed upon cities and towns under this chapter shall include obligations established in the rules of the supreme judicial court and in the regulations of the jury commissioner made and duly promulgated under the provisions of this chapter. Cities and towns having boards of election commissioners or boards of registrars of voters may by letter to the jury commissioner signed by the executive head of the city or town delegate certain responsibilities under this chapter to such boards, but ultimate responsibility for compliance shall not be delegated.