BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Gross-Berlin Dating: 15.11.1907
BRIEF [O.A.] Döring, Adolf G... Author: Döring, Adolf G... Recipient: Haeckel, Ernst Dating: 31.12.1908
BRIEF [O.A.] Schwarz, Elisabeth Author: Schwarz, Elisabeth Recipient: Haeckel, Ernst Dating: 25.05.1910