BRIEF [O.A.] Habellock, Herbert Author: Habellock, Herbert Recipient: Haeckel, Ernst Dating: 17.02.1918
BRIEF [O.A.] Taesler, Clemens; Damroese, Waldemar; Roese, Emil Author: Taesler, Clemens; Damroese, Waldemar; Roese, Emil Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Danzig Dating: 21.09.1918
BRIEF [O.A.] Lakowitz, Konrad Author: Lakowitz, Konrad Recipient: Haeckel, Ernst Corporation: Naturforschende Gesellschaft zu Danzig Dating: 14.02.1918
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 20.11.1918
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 01.07.1918