BRIEF [O.A.] Müller-Brauel, Hans Author: Müller-Brauel, Hans Recipient: Haeckel, Ernst Dating: 25.02.1897
POSTKARTE Focke, Wilhelm Olbers Author: Focke, Wilhelm Olbers Recipient: Haeckel, Ernst Dating: 04.08.1897
BRIEF OHNE UMSCHLAG Schwerdtfeger, G. Author: Schwerdtfeger, G. Recipient: Haeckel, Ernst Corporation: Städtisches Museum Bremen Dating: 11.01.1897