BILDPOSTKARTE Reinicke, Emanuel Author: Reinicke, Emanuel Recipient: Haeckel, Ernst Dating: 14.07.1913
BILDPOSTKARTE Haeckel, Walther Author: Haeckel, Walther Recipient: Haeckel, Ernst; Haeckel, Agnes [Eltern] Dating: 04.06.1913
BILDPOSTKARTE Aigner, Eduard Author: Aigner, Eduard Recipient: Haeckel, Ernst Corporation: Deutscher Monistenbund Dating: 09.09.1913