BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Walter Dating: 14.12.1919
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