The members who are first appointed shall serve for terms of one, two, three, four and five years, respectively, from the date of their appointment as shall be specified at the time of their appointment. Thereafter, the term of office shall be five years. A member shall hold office until his successor has been appointed. Vacancies for unexpired terms shall be promptly filled by the appointing power. A member shall receive no compensation for his services, but shall be entitled to the necessary expenses, including traveling expenses, incurred in the discharge of his duties.