To this it is answered, first, that the defendant, by pleading over, after the plea to the jurisdiction was adjudged insufficient, finally waived all benefit of that plea.

When that plea was adjudged insufficient, the defendant was obliged to answer over. He held no alternative. He could not stop the further progress of the case in the Circuit Court by a writ of error, on which the sufficiency of his plea to the jurisdiction could be tried in this court, because the judgment on that plea was not final, and no writ of error would lie. He was forced to plead to the merits. It cannot be true, then, that he waived the benefit of his plea to the jurisdiction by answering over. Waiver includes consent. Here, there was no consent. And if the benefit of the plea was finally lost, it must be, not by any waiver, but because the laws of the United States have not provided any mode of reviewing the decision of the Circuit Court on such a plea, when that decision is against the defendant. This is not the law. Whether the decision of the Circuit Court on a plea to the jurisdiction be against the plaintiff, or against the defendant, the losing party may have any alleged error in law, in ruling such a plea, examined in this court on a writ of error, when the matter in controversy exceeds the sum or value of two thousand dollars. If the decision be against the plaintiff, and his suit dismissed for want of jurisdiction, the judgment is technically final, and he may at once sue out his writ of error. (Mollan v. Torrance, 9 Wheat., 537.) If the decision be against the defendant, though he must answer over, and wait for a final judgment in the cause, he may then have his writ of error, and upon it obtain the judgment of this court on any question of law apparent on the record, touching the jurisdiction. The fact that he pleaded over to the merits, under compulsion, can have no effect on his right to object to the jurisdiction. If this were not so, the condition of the two parties would be grossly unequal. For if a plea to the jurisdiction were ruled against the plaintiff, he could at once take his writ of error, and have the ruling reviewed here; while, if the same plea were ruled against the defendant, he must not only wait for a final judgment, but could in no event have the ruling of the Circuit Court upon the plea reviewed by this court. I know of no ground for saying that the laws of the United States have thus discriminated between the parties to a suit in its courts.

It is further objected, that as the judgment of the Circuit Court was in favor of the defendant, and the writ of error in this cause was sued out by the plaintiff, the defendant is not in a condition to assign any error in the record, and therefore this court is precluded from considering the question whether the Circuit Court had jurisdiction.

The practice of this court does not require a technical assignment of errors. (See the rule.) Upon a writ of error, the whole record is open for inspection; and if any error be found in it, the judgment is reversed. (Bank of U.S. v. Smith, 11 Wheat., 171.)

It is true, as a general rule, that the court will not allow a party to rely on anything as cause for reversing a judgment, which was for his advantage. In this, we follow an ancient rule of the common law. But so careful was that law of the preservation of the course of its courts, that it made an exception out of that general rule, and allowed a party to assign for error that which was for his advantage, if it were a departure by the court itself from its settled course of procedure. The cases on this subject are collected in Bac. Ab., Error H. 4. And this court followed this practice in Capron v. Van Noorden, (2 Cranch, 126,) where the plaintiff below procured the reversal of a judgment for the defendant, on the ground that the plaintiff's allegations of citizenship had not shown jurisdiction.

But it is not necessary to determine whether the defendant can be allowed to assign want of jurisdiction as an error in a judgment in his own favor. The true question is, not what either of the parties may be allowed to do, but whether this court will affirm or reverse a judgment of the Circuit Court on the merits, when it appears on the record, by a plea to the jurisdiction, that it is a case to which 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. Owings, (17 How., 47.)

When, therefore, as in this case, the necessary averments as to citizenship are made on the record, and jurisdiction is assumed to exist, and the defendant comes by a plea to the jurisdiction to displace that presumption, he occupies, in my judgment, precisely the position described in Bacon Ab., Abatement: "Abatement, in the general acceptation of the word, signifies a plea, put in by the defendant, in which he shows cause to the court why he should not be impleaded; or, if at all, not in the manner and form he now is."