In each ward a supervisor, 2 aldermen and a constable shall be elected: Provided, That the council of any city re-incorporated under and made subject to the provisions of this act, which at the time of such re-incorporation shall have but 2 wards, may provide by ordinance for the election of 2 additional aldermen, to be known as aldermen at large, and to be elected by the qualified electors of the whole city. At the first election held under this act 1 of such aldermen shall be elected for a term of 1 year and 1 for a term of 2 years, and annually thereafter 1 shall be elected for a term of 2 years.