"...there can be no doubt that the jury has an `unreviewable and unreversible power...to acquit in disregard of the instructions on the law given by the trial judge....'" U.S. v Dougherty, 473 F.2d 1113, 1139 (1972).
Other info related to Dougherty case: 16 Am Jur 2d, Sec. 177.

"In criminal cases juries remained the judges of both law and fact for approximately fifty years after the Revolution. However, the judges in America, just as in England after the Revolution of 1688, gradually asserted themselves increasingly through their instructions on the law.
"We recognize, as appellants urge, the undisputed power of the jury to acquit, even if its verdict is contrary to the law as given by the judge and contrary to the evidence."
U.S. v Moylan, 417 F.2d 1002,1006 (1969)

"It may not be amiss...to remind you of the good old rule, that on the question of fact, it is the province of the jury, and on the question of law, it is the province of the court to decide. But, it must be observed that by law...you have nevertheless a right to take it upon yourselves to judge both, in controversy...both objects are lawfully within your power of decision." Justice John Jay to the jury, Georgia v. Brailsford, 3 Dall. 1, 4 (1794), 1 L.Ed. 483. "...for as, on the one hand, it is presumed that juries are the best judges of facts; it is, on the other hand, presumable, that the court are the best judges of law. But still, both objects are lawfully within your power of decision."

Sparf v. United States, 156 U.S. 51 (1895) http://laws.findlaw.com/us/156/51.html
'It may not be amiss here, gentlemen, to remind you of the good old rule that on questions of fact it is the province of the jury, on questions of law it is the province of the court, to decide. But it must be observed that, by the same law which recognizes this reasonable distribution of jurisdiction, you have, nevertheless, a right to take [156 U.S. 51, 65] upon yourselves to judge of both, and to determine the law as well as the fact in controversy.

...the jury has "...the power to bring in a verdict in the teeth of both law and facts."
Oliver Wendell Holmes, Horning v D.C., 254 U.S. 135, 138, 41 S.Ct. 53, 54, 65 L.Ed. 185 (1920)

"...no fact tried by a jury shall be otherwise reexamined in any court of the United States, than according to the rules of the common law." U.S. Constitution, 7th Amendment. Only another common law jury can review a decision of a jury. There is no other appeal. Not even the Supreme Court can review a jury's decision.

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[See also:] U.S. v. Moylan, 417 F.2d 1002 (1969)