h the
judicial power of the United States does not extend. The course of the
court is, where no motion is made by either party, on its own motion,
to reverse such a judgment for want of jurisdiction, not only in cases
where it is shown, negatively, by a plea to the jurisdiction, that
jurisdiction does not exist, but even where it does not appear,
affirmatively, that it does exist. (Pequignot _v._ The Pennsylvania
R.R. Co., 16 How., 104.) It acts upon the principle that the judicial
power of the United States must not be exerted in a case to which it
does not extend, even if both parties desire to have it exerted.
(Cutler _v._ Rae, 7 How., 729.) I consider, therefore, that when there
was a plea to the jurisdiction of the Circuit Court in a case brought
here by a writ of error, the first duty of this court is, _sua
sponte_, if not moved to it by either party, to examine the
sufficiency of that plea; and thus to take care that neither the
Circuit Court nor this court shall use the judicial power of the
United States in a case to which the Constitution and laws of the
United States have not extended that power.

I proceed, therefore, to examine the plea to the jurisdiction.

I do not perceive any sound reason why it is not to be judged by the
rules of the common law applicable to such pleas. It is true, where
the jurisdiction of the Circuit Court depends on the citizenship of
the parties, it is incumbent on the plaintiff to allege on the record
the necessary citizenship; but when he has done so, the defendant must
interpose a plea in abatement, the allegations whereof show that the
court has not jurisdiction; and it is incumbent on him to prove the
truth of his plea.

In Sheppard _v._ Graves, (14 How., 27,) the rules on this subject are
thus stated in the opinion of the court: "That although, in the courts
of the United States, it is necessary to set forth the grounds of
their cognizance as courts of limited jurisdiction, yet wherever
jurisdiction shall be averred in the pleadings, in conformity with the
laws creating those courts, it must be taken, _prima facie_, as
existing; and it is incumbent on him who would impeach that
jurisdiction for causes dehors the pleading, to allege and prove such
causes; that the necessity for the allegation, and the burden of
sustaining it by proof, both rest upon the party taking the
exception." These positions are sustained by the authorities there
cited, as well as by Wickliffe _v._ O