The children of slaves born within the limits of this State after the fourth day of July, eighteen hundred and sixty-three, shall be free; and all slaves within the said State who shall, at the time aforesaid, be under the age of ten years, shall be free when they arrive at the age of twenty-one years; and all slaves over ten and under twenty-one years, shall be free when they arrive at the age of twenty-five years; and no slave shall be permitted to come into the State for permanent residence therein.