BRIEF [O.A.] Knieling, Johs... W... Author: Knieling, Johs... W... Recipient: Haeckel, Ernst Dating: 22.02.1919
BRIEF [O.A.] Jacoby, H... E... L... Author: Jacoby, H... E... L... Recipient: Haeckel, Ernst Dating: 14.02.1919