18. (1) Any person objecting to an order passed by an Appellate Assistant Commissioner imposing on him a penalty under section 16 or enhancing his assessment or enhancing a penalty under section 17 may appeal to the Commissioner within thirty days of the date on which he was served with notice of such order. (2) In disposing of the appeal the Commissioner may, after giving the appellant an opportunity of being heard, pass such orders thereon as he thinks fit. (3) On the coming into operation of Part II of the Indian Income-tax (Amendment) Act, 1939, this section shall cease to have effect.