BRIEF OHNE UMSCHLAG Sokolowsky, Alexander Author: Sokolowsky, Alexander Recipient: Haeckel, Ernst Dating: 14.02.1919
BRIEF [O.A.] Thinius, Carl Author: Thinius, Carl Recipient: Haeckel, Ernst Corporation: Pfadweiser-Verlag Dating: 14.02.1919
BRIEF [O.A.] Michelsohn, Julius Author: Michelsohn, Julius Recipient: Haeckel, Ernst Dating: 15.08.1919