BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Grober, Julius Dating: 30.04.1917
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Grober, Julius Dating: 25.07.1917
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Engelmann, Wilhelm Dating: 17.07.1917
POSTKARTE Haeckel, Ernst Author: Haeckel, Ernst Recipient: Verworn, Max; Verworn, Josephine Dating: 22.02.1917
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Uslar-Gleichen, Bernhard von Dating: 05.09.1917
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Uslar-Gleichen, Bernhard von Dating: 11.12.1917