“The instant I felt it I wanted to own it,” wrote Peggy Guggenheim in her 1979 autobiography, Out of this Century. She was referring to Head and Shell by the French-German sculptor Jean Arp. Guggenheim bought the bronze sculpture, and Arp, a founder of the Dada movement, became the first artist to enter her collection. More than 70 works by Arp—from signature sculptures to painted reliefs and drawings—range over six decades of radical work. —J.V.