BRIEF [O.A.] Sethe, Bertha Author: Sethe, Bertha Recipient: Haeckel, Ernst Dating: vermutlich Mai 1892
BRIEF [O.A.] Harden, Maximilian Author: Harden, Maximilian Recipient: Haeckel, Ernst Corporation: Die Zukunft Dating: 27.10.1892
BRIEF [O.A.] Harden, Maximilian Author: Harden, Maximilian Recipient: Haeckel, Ernst Corporation: Die Zukunft Dating: 03.11.1892
BRIEF [O.A.] Harden, Maximilian Author: Harden, Maximilian Recipient: Haeckel, Ernst Corporation: Die Zukunft Dating: 17.11.1892