General municipal or city elections shall be held annually on the first Saturday in December in each year, the first such election to be held on the first Saturday in December, 1929. All city officers elected at the December election, 1929, shall be and constitute the officers under this Charter and hold office for the term for which they are, elected. The six councilmen incumbent from the various wards whose terms do not expire until January, 1931, shall continue in office until their said terms expire.