POSTKARTE Bölsche, Wilhelm; Bölsche, Karl Author: Bölsche, Wilhelm; Bölsche, Karl Recipient: Haeckel, Ernst Dating: 01.10.1904
POSTKARTE Morawetz-Dierkes, Leopoldine von Author: Morawetz-Dierkes, Leopoldine von Recipient: Haeckel, Ernst Dating: 06.03.1904
POSTKARTE Witzleben, Karl von Author: Witzleben, Karl von Recipient: Haeckel, Ernst Dating: 31.12.1904