In the case of a third class fireman on probation having been notified that he will not receive permanent appointment, his employment shall thereupon cease. In all other cases of a probationer being notified that he will not receive permanent appointment, and in the case of removal or replacement of the chief of the department, such person may resume his former position and pay scale in the department, and the last appointee in a position subordinate thereto and in line of promotion shall resume his former position and pay scale respectively. The name of the person in the lowest position thus affected and who necessarily retires from service because of resumption by the probationer, or replacement of the chief of the department, shall be placed on the appropriate register for certification. (C.O. 10 § 8, 11-13-67.)