BRIEF [O.A.] Grimsehl, Carl Author: Grimsehl, Carl Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Berlin Dating: 22.01.1914
BRIEF [O.A.] Grimsehl, Carl Author: Grimsehl, Carl Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Berlin Dating: 07.08.1914
BRIEF [O.A.] Glossy, Karl Author: Glossy, Karl Recipient: Haeckel, Ernst Corporation: Österreichische Rundschau Dating: 10.12.1914
BRIEF [O.A.] N.N. Author: N.N. Recipient: Haeckel, Ernst Corporation: Goethe-Bund Berlin Dating: 23.03.1914