The Civil Service Commission shall consist of three electors of the municipality not holding other municipal office or appointment, to be appointed by the Mayor, with the concurrence of a majority of the members elected to Council, for terms of six years each, commencing on January 25th of such year, except that one of the three electors first appointed shall be designated by the Mayor to serve for a term of two years and one for a term of four years. A vacancy occurring during the term of any member of the Commission shall be filled for the unexpired term in the manner authorized for an original appointment.