BRIEF OHNE UMSCHLAG Recipient: Haeckel, Ernst Corporation: Kosmos-Ges. der Naturfreunde Dating: 28.10.1907
BRIEF [O.A.] Loewenthal, Kaethe Author: Loewenthal, Kaethe Recipient: Haeckel, Ernst Dating: ??.08.1919
BRIEF [O.A.] Ziegler, Heinrich Ernst Author: Ziegler, Heinrich Ernst Recipient: Haeckel, Ernst Dating: 10.08.1919