BRIEF [O.A.] Burkhardt, Theobald Author: Burkhardt, Theobald Recipient: Haeckel, Ernst Dating: 28.02.1908
BRIEF [O.A.] Kilian, Waldemar C... Author: Kilian, Waldemar C... Recipient: Haeckel, Ernst Dating: 31.05.????
POSTKARTE Kilian, Waldemar C... Author: Kilian, Waldemar C... Recipient: Haeckel, Ernst Dating: 24.12.????
BRIEF [O.A.] Kilian, Waldemar C... Author: Kilian, Waldemar C... Recipient: Haeckel, Ernst Dating: 15.02.1914
BRIEF [O.A.] Wölfling, Friedrich Author: Wölfling, Friedrich Recipient: Haeckel, Ernst Dating: 19.09.1915