BRIEF [O.A.] Theszóll, Charles Author: Theszóll, Charles Recipient: Haeckel, Ernst Dating: 23-02-1900
BRIEF [O.A.] Haimann, Heinrich Author: Haimann, Heinrich Recipient: Haeckel, Ernst Dating: 12.01.1905
BRIEF [O.A.] Haller, I... [Gräfin] Author: Haller, I... [Gräfin] Recipient: Haeckel, Ernst Dating: 22.11.1916
BRIEF [O.A.] Haller, I... [Gräfin] Author: Haller, I... [Gräfin] Recipient: Haeckel, Ernst Dating: 12.12.1916