It is not necessary to aver the capacity of a party to sue or be sued, the authority of a party to sue or be sued in a representative capacity, or the legal existence of an artificial person that is made a party. When a party desires to raise an issue as to the legal existence of any party or the capacity of any party to sue or be sued, or the authority of a party to sue and be sued in a representative capacity, he shall do so by specific negative averment which shall include such particulars as are peculiarly within his knowledge.