BRIEF [O.A.] Anton, Günther Kurt Author: Anton, Günther Kurt Recipient: Haeckel, Ernst Dating: 03.01.1901
ANSICHTSKARTE Basso, Fritzi von Author: Basso, Fritzi von Recipient: Haeckel, Ernst Dating: 07.03.1912
BRIEF [O.A.] Sluiter, C... Ph... Author: Sluiter, C... Ph... Recipient: Haeckel, Ernst Dating: 10.04.1882