“ Respondent, Hawkeye-Security Insurance Company, filed a motion to quash the return of service of summons on the grounds that the District Court acquired no personal jurisdiction over it and that the power of attorney which it had filed with the Commissioner of Motor Vehicles of the State of Wisconsin did not authorize him to accept service of process for it in this case. After this motion was denied, respondent filed its answer to the complaint in which it again pressed its claim that the District Court lacked personal jurisdiction over it. ”