BRIEF [O.A.] Hanitsch, Richard Author: Hanitsch, Richard Recipient: Haeckel, Ernst Dating: 04.08.1886
BRIEF [O.A.] Köhler, Fritz Author: Köhler, Fritz Recipient: Haeckel, Ernst Corporation: Naturforschende Gesellschaft des Osterlandes Dating: 11.08.1919
BRIEF [O.A.] Geibel, Stephan Author: Geibel, Stephan Recipient: Haeckel, Ernst Corporation: Piepersche Hofbuchdruckerei Dating: 27.09.1901
BRIEF [O.A.] Moritz von Sachsen-Altenburg [Herzog] Author: Moritz von Sachsen-Altenburg [Herzog] Recipient: Haeckel, Ernst Dating: 19.11.1900