BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Danzig Dating: 15.02.1913
BRIEF [O.A.] Lewinsky, Bernhard Author: Lewinsky, Bernhard Recipient: Haeckel, Ernst Dating: 18.02.1912
BRIEF [O.A.] Lewinsky, Bernhard Author: Lewinsky, Bernhard Recipient: Haeckel, Ernst Dating: 15.02.1914
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 15.06.1902
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 15.02.1902
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 20.12.1901
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 03.12.1901
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 27.09.1901