BRIEF [O.A.] Schaufenbühl, Friedrich Author: Schaufenbühl, Friedrich Recipient: Haeckel, Ernst Dating: 17.12.1915
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Weimar Dating: 16.02.1915
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 15.02.1915
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 03.05.1915
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 04.07.1915