BRIEF [O.A.] Barbulowitsch, Boguljub S. Author: Barbulowitsch, Boguljub S. Recipient: Haeckel, Ernst Dating: 03.11.1913
BRIEF OHNE UMSCHLAG Radowanowic, Marinko Author: Radowanowic, Marinko Recipient: Haeckel, Ernst Dating: 28.11.1875
TELEGRAMM Ivezic, Gerassim P. Author: Ivezic, Gerassim P. Recipient: Haeckel, Ernst Dating: 16.02.1909