BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Kunstgewerbehaus Koenig & Lengsfeld Dating: 13.08.1919
BRIEF [O.A.] Riess, Carl Author: Riess, Carl Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Dating: 19.03.1919
POSTKARTE Riess, Carl Author: Riess, Carl Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Dating: 18.04.1919
POSTKARTE Riess, Carl Author: Riess, Carl Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Dating: 13.05.1919
BRIEF [O.A.] Michelsohn, Julius Author: Michelsohn, Julius Recipient: Haeckel, Ernst Dating: 20.01.1919
BRIEF [O.A.] Michelsohn, Julius Author: Michelsohn, Julius Recipient: Haeckel, Ernst Dating: 22.04.1919
BRIEF [O.A.] Michelsohn, Julius Author: Michelsohn, Julius Recipient: Haeckel, Ernst Dating: 24.04.1919