The term of office of the members shall be three years, but of the first six appointed, the term of the first two shall end on the second Monday in January, 1972 and January, 1973 and the last two shall end on the second Monday in January, 1974. The terms of the first six members appointed shall be fixed and designated by the mayor at the time of such appointment. The term of the seventh member shall begin on the second Monday of January, 1981.