BRIEF [O.A.] Maurer, Friedrich Author: Maurer, Friedrich Recipient: Haeckel, Ernst Dating: 11.08.1919
BRIEF [O.A.] Hacker, G... H... Author: Hacker, G... H... Recipient: Haeckel, Ernst Corporation: Grossherzoglich Hessisches Hoftheater Dating: 08.08.1906
BRIEF [O.A.] Hardenberg Author: Hardenberg Recipient: Haeckel, Ernst Corporation: Großherzogliches Hofmarschallamt Dating: 24.09.1917