BRIEF [O.A.] Engelmann, Richard Author: Engelmann, Richard Recipient: Haeckel, Ernst Dating: 20.03.1919
BRIEF [O.A.] Fuchsel, A... Author: Fuchsel, A... Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Weimar Dating: 12.08.1919
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 15.02.1919
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 27.02.1919
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 03.08.1919