BRIEF [O.A.] Sieber, Hans (Johannes) Author: Sieber, Hans (Johannes) Recipient: Haeckel, Ernst Dating: 14.07.1910
BRIEF [O.A.] Hoffmann, Georg Author: Hoffmann, Georg Recipient: Haeckel, Ernst Corporation: Kulturgesellschaft Ernst Abbe K.E.A. Dating: 20.12.1910
BRIEF [O.A.] Hoffmann, Georg Author: Hoffmann, Georg Recipient: Haeckel, Ernst Corporation: Der Kulturarzt Dating: 26.12.1910
BRIEF [O.A.] Hoffmann, Georg Author: Hoffmann, Georg Recipient: Haeckel, Ernst Corporation: Der Kulturarzt Dating: 19.12.1910