BRIEF [O.A.] Boenigk, Otto Freiherr von Author: Boenigk, Otto Freiherr von Recipient: Haeckel, Ernst Dating: 18.08.1918
BRIEF [O.A.] Boenigk, Otto Freiherr von Author: Boenigk, Otto Freiherr von Recipient: Haeckel, Ernst Dating: 05.05.1919