BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Charlotte Dating: 13.04.1873
BRIEF [O.A.] Délyanny, Théodore Author: Délyanny, Théodore Recipient: Haeckel, Ernst Dating: 21.06.1896
BRIEF [O.A.] Georgionpoulos, S... Author: Georgionpoulos, S... Recipient: Haeckel, Ernst Dating: 10.11.1906
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Bibliothèque Nationale Ottomane Dating: 18.03.1911