BRIEF [O.A.] Soldat, J... H... Author: Soldat, J... H... Recipient: Haeckel, Ernst Dating: 03.06.1914
BRIEF [O.A.] Schön, Amelie von Author: Schön, Amelie von Recipient: Haeckel, Ernst Dating: 16.11.1918
BRIEF [O.A.] Soldat, J... H... Author: Soldat, J... H... Recipient: Haeckel, Ernst Dating: 30.12.1915