BRIEF [O.A.] Bär-Ulrich, Marie Author: Bär-Ulrich, Marie Recipient: Haeckel, Ernst Dating: ??.02.1904
BRIEF [O.A.] Wundsam, Julius V. Ed. Author: Wundsam, Julius V. Ed. Recipient: Haeckel, Ernst Dating: 12.12.1904
BRIEF OHNE UMSCHLAG Müller, Albert Author: Müller, Albert Recipient: Haeckel, Ernst Dating: 07.05.1904