BRIEF [O.A.] Friedenthal, Albert Author: Friedenthal, Albert Recipient: Haeckel, Ernst Dating: 18.07.1909
BRIEF [O.A.] Gadeau de Kerville, Henri Author: Gadeau de Kerville, Henri Recipient: Haeckel, Ernst Dating: 20.05.1909
BRIEF [O.A.] Fischer, Johannes Author: Fischer, Johannes Recipient: Haeckel, Ernst Dating: 10.02.1909
BRIEF [O.A.] Lieber, Gabriele von Author: Lieber, Gabriele von Recipient: Haeckel, Ernst Corporation: Frauenverlag Dating: 27.11.1909