When a defendant in any suit brought under the provisions of this article is an infant or insane person, a guardian ad litem shall be appointed as provided by section ten, article four, chapter fifty-six of this code, and shall be governed by the provisions of said section, and when a defendant is a convict, a guardian ad litem shall be appointed by the court, who shall have the same rights and duties as those of a guardian ad litem for an infant or insane person: Provided, That no guardian ad litem need be appointed for parties unknown, though they be infant, insane or convict.
