21. Where no such provision exists, a writ of summons against a corporation may be served by leaving an office copy of the writ with the President or other head officer, or the clerk, treasurer, or secretary of the corporation, and a writ of summons against a public company may be served by leaving with the secretary, manager or other person authorized to transact the business of the company in Cyprus an office copy of the writ or by leaving the same at the office of the company.