The party amending shall point out the instrument amended, as "original petition," or "plaintiff's first supplemental petition," or as "original answer," or "defendant's first supplemental answer" or other instrument file by the party and shall amend by filing a substitute therefor, entire and complete in itself, indorsed "amended original petition," or "amended first supplemental petition," or "amended original answer," or "amended first supplemental answer," accordingly as said instruments of pleading are designated.