BRIEF [O.A.] Kreutzer, Erwin Rud. Author: Kreutzer, Erwin Rud. Recipient: Haeckel, Ernst Dating: 07.03.1904
POSTKARTE Obersteiner, Wolfgang Author: Obersteiner, Wolfgang Recipient: Haeckel, Ernst Dating: 06.08.1904
BRIEF [O.A.] Novak, Terese Author: Novak, Terese Recipient: Haeckel, Ernst Corporation: Zsch. Zensky Svet Dating: 10.02.1904
TELEGRAMM Recipient: Haeckel, Ernst Corporation: Akademischer Verein deutscher Naturforscher Dating: 16.02.1904