BRIEF [O.A.] Ziegler, Heinrich Ernst Author: Ziegler, Heinrich Ernst Recipient: Haeckel, Ernst Dating: 18.04.1914
BRIEF [O.A.] Ziegler, Heinrich Ernst Author: Ziegler, Heinrich Ernst Recipient: Haeckel, Ernst Dating: 28.03.1915
BRIEF [O.A.] Ziegler, Heinrich Ernst Author: Ziegler, Heinrich Ernst Recipient: Haeckel, Ernst Dating: 10.08.1919
TELEGRAMM Ziegler, Heinrich Ernst Author: Ziegler, Heinrich Ernst Recipient: Haeckel, Ernst Dating: 16.02.1914