Mookini v. United State, 303 U.S. 201 (1938):

The term 'District Courts of the United States,' as used in the rules, without an addition expressing a wider connotation, has its historic significance. It describes the constitutional courts created under article 3 of the Constitution. Courts of the Territories are legislative courts, properly speaking, and are not District Courts of the United States. We have often held that vesting a territorial court with jurisdiction similar to that vested in the District Courts of the United States does not make it a 'District Court of the United States.' Reynolds v. United States, 98 U.S. 145 , 154; The City of Panama, 101 U.S. 453 , 460; In re Mills, 135 U.S. 263, 268 , 10 S.Ct. 762; McAllister v. United States, 141 U.S. 174, 182 , 183 S., 11 S.Ct. 949; Stephens v. Cherokee Nation, 174 U.S. 445, 476 , 477 S., 19 S.Ct. 722; Summers v. United States, 231 U.S. 92, 101 , 102 S., 34 S.Ct. 38; United States v. Burroughs, 289 U.S. 159, 163 , 53 S.Ct. 574. Not only did the promulgating order use the term District Courts of the United States in its historic and proper sense, but the omission of provision for the application of the rules to the territorial courts and other courts mentioned in the authorizing act clearly shows the limitation that was intended.

[Mookini v. United State, 303 U.S. 201 (1938)]