BRIEF [O.A.] Faber, Emily M... Author: Faber, Emily M... Recipient: Haeckel, Ernst Dating: 22.02.1912
BRIEF [O.A.] Caballero, Fernan Author: Caballero, Fernan Recipient: Haeckel, Ernst Dating: 13.01.1893
BILDPOSTKARTE Crompton, Ella von Author: Crompton, Ella von Recipient: Haeckel, Ernst Dating: 15.08.1917
BRIEF [O.A.] Bojanowski, Paul von Author: Bojanowski, Paul von Recipient: Haeckel, Ernst Corporation: Weimar-Sammlung Dating: 15.02.1915
BRIEF [O.A.] Engelmann, Richard Author: Engelmann, Richard Recipient: Haeckel, Ernst Dating: 20.03.1919