BRIEF [O.A.] Fürbringer, Fanny Author: Fürbringer, Fanny Recipient: Haeckel, Ernst Dating: 10.11.1901
BRIEF [O.A.] Eggeling, Heinrich von Author: Eggeling, Heinrich von Recipient: Haeckel, Ernst Dating: 17.02.1891
BRIEF [O.A.] Eggeling, Heinrich von Author: Eggeling, Heinrich von Recipient: Haeckel, Ernst Dating: 15.02.1894
BRIEF [O.A.] Fleischer, Richard Author: Fleischer, Richard Recipient: Haeckel, Ernst Dating: 29.04.1874
BRIEF [O.A.] Fleischer, Richard Author: Fleischer, Richard Recipient: Haeckel, Ernst Dating: 07.05.1874