The said respective boards of supervisors in each county, entitled to more than 1 representative in the state legislature, shall have power and it shall be their duty, at their annual meeting in the year 1851, and at their annual meeting next after each subsequent apportionment of such representatives by the legislature, to divide their respective counties into representative districts, equal in number to the number of representatives to which such county is entitled by law, in accordance with section 3 of article 4 of the constitution of this state; and they shall cause to be filed in the office of the secretary of state, and in the office of the clerk of such county, within 30 days after such division, a description of such representative districts, specifying the number of each district, and the population thereof, according to the last preceding enumeration.