BRIEF [O.A.] Margittai, Richard Author: Margittai, Richard Recipient: Haeckel, Ernst Dating: 14.02.1916
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