BILDPOSTKARTE Magnussen, Harro; Häberlin, Carl Author: Magnussen, Harro; Häberlin, Carl Recipient: Haeckel, Ernst Dating: 15.06.1907
BILDPOSTKARTE Haeckel, Walther Author: Haeckel, Walther Recipient: Schmidt, Ernst [incognito Ernst Haeckel] Dating: 30.03.1907
BILDPOSTKARTE Ihering, Hermann von Author: Ihering, Hermann von Recipient: Haeckel, Ernst Dating: 23.04.1907
BILDPOSTKARTE Haynes, Frank Jay; Haynes, Jack Author: Haynes, Frank Jay; Haynes, Jack Recipient: Haeckel, Ernst Dating: 17.08.1907
BILDPOSTKARTE Sokolowsky, Alexander Author: Sokolowsky, Alexander Recipient: Haeckel, Ernst Dating: 23.05.1907