BRIEF [O.A.] Bloch, Iwan Author: Bloch, Iwan Recipient: Haeckel, Ernst Corporation: Zeitschrift für Sexualwissenschaft Dating: 18.09.1917
BRIEF [O.A.] Borngräber, Otto Author: Borngräber, Otto Recipient: Haeckel, Ernst Corporation: Neues Theater zu Berlin Dating: 20.05.1908
BRIEF [O.A.] Klostermann, Helene Author: Klostermann, Helene Recipient: Haeckel, Ernst Dating: 02.01.1897