BILDPOSTKARTE Kükenthal, Willy Georg Author: Kükenthal, Willy Georg Recipient: Haeckel, Ernst Dating: 23.07.1906
BRIEF OHNE UMSCHLAG Beinling, Rudolf Theodor Author: Beinling, Rudolf Theodor Recipient: Haeckel, Ernst Dating: 11.03.1872
TELEGRAMM Gerhardt, Ulrich [et al.] Author: Gerhardt, Ulrich [et al.] Recipient: Haeckel, Ernst Dating: 16.02.1914
BRIEF OHNE UMSCHLAG Haeckel, Eduard Author: Haeckel, Eduard Recipient: Haeckel, Ernst Dating: 26.11.1910
