Section 33A. When any interest in real or personal property is limited, mediately or immediately, in an otherwise effective testamentary conveyance or devise, in form or in effect, to the heirs or next of kin of the conveyor, or to a person or persons who on the death of the conveyor are some or all of his heirs or next of kin, such conveyees or devisees acquire the interest that the conveyance or devise purports to create by purchase and not by descent.