BRIEF OHNE UMSCHLAG Andersen, Hendrik Christian Author: Andersen, Hendrik Christian Recipient: Haeckel, Ernst Dating: 28.05.1914
BRIEF OHNE UMSCHLAG Allmers, Hermann Author: Allmers, Hermann Recipient: Haeckel, Ernst Dating: 06.06.1889
POSTKARTE Bölsche, Wilhelm; Bölsche, Johanna Author: Bölsche, Wilhelm; Bölsche, Johanna Recipient: Haeckel, Ernst Dating: 01.05.1905
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Delle Grazie, Marie Eugenie Dating: 17.10.1899