POSTKARTE Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 20.05.1910
BRIEF [O.A.] Vogt, H... Author: Vogt, H... Recipient: Haeckel, Ernst Corporation: Foner & Vogt; Atellier für wissenschaftliche Projection Dating: 12.11.1913
POSTKARTE Hübbe-Schleiden, Wilhelm Author: Hübbe-Schleiden, Wilhelm Recipient: Haeckel, Ernst Dating: 30.07.1894
BRIEF [O.A.] Schäfer, Dietrich Author: Schäfer, Dietrich Recipient: Haeckel, Ernst Dating: 14.10.1904
BRIEF [O.A.] Schäfer, Dietrich Author: Schäfer, Dietrich Recipient: Haeckel, Ernst Dating: 30.10.1904
BRIEF [O.A.] Schäfer, Dietrich Author: Schäfer, Dietrich Recipient: Haeckel, Ernst Dating: 05.11.1904