BRIEF OHNE UMSCHLAG Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 13.02.1904
BRIEF OHNE UMSCHLAG Kropp, Diedrich Author: Kropp, Diedrich Recipient: Haeckel, Ernst Dating: 15.02.1904
BRIEF [O.A.] Schauinsland, H... Author: Schauinsland, H... Recipient: Haeckel, Ernst Corporation: Städtisches Museum für Natur-, Völker- u. Handelskunde Dating: 18.02.1904