Jurisdiction allocation for Commissioners of Income tax: statutory notifications must precede creation or deletion of administrative circles to avoid legal uncertainty. Jurisdiction over Commissioners of Income tax is conferred exclusively by the Board via notification under section 121. Commissioners must not create or delete administrative circles without prior reference to the Board because notifications cannot be given retrospective effect to regularise such changes; proposals for creation or deletion of circles should be submitted to the Board well in advance so the notification can be issued in time.