BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Walter Dating: 10.11.1919
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Walter Dating: 14.12.1919
BRIEF OHNE UMSCHLAG Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Schmidt, Heinrich Dating: 28.10.1920
BILDPOSTKARTE Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 30.04.1914
BRIEF OHNE UMSCHLAG Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Julius Dating: 24.02.1903
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 15.06.1902
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 15.02.1902