BRIEF [O.A.] Habellock, Herbert Author: Habellock, Herbert Recipient: Haeckel, Ernst Dating: 15.02.1913
BRIEF [O.A.] Sokolovski, Katharina von Author: Sokolovski, Katharina von Recipient: Haeckel, Ernst Dating: 01.12.1913
BRIEF [O.A.] Scholz, Friedrich Author: Scholz, Friedrich Recipient: Haeckel, Ernst Dating: 14.02.1913
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund, Ortsgruppe Danzig Dating: 15.02.1913