POSTKARTE Haeckel, Walther Author: Haeckel, Walther Recipient: Haeckel, Ernst Dating: 1904.??.?? - 1905.??.??
KARTE Willkomm-Schneider, Martha Author: Willkomm-Schneider, Martha Recipient: Haeckel, Ernst Dating: 16.02.1914
BRIEF [O.A.] Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 06.06.1884
DOKUMENT Moleschott, Carlo; Moleschott, Elsa Author: Moleschott, Carlo; Moleschott, Elsa Recipient: Haeckel, Ernst Dating: 20.05.1893