BRIEF [O.A.] Burckhardt, Rud... Author: Burckhardt, Rud... Recipient: Haeckel, Ernst Dating: 26.02.1899
BRIEF [O.A.] Ziegler, Heinrich Ernst Author: Ziegler, Heinrich Ernst Recipient: Haeckel, Ernst Dating: 14.10.1899
BRIEF [O.A.] Zschokke, Friedrich Author: Zschokke, Friedrich Recipient: Haeckel, Ernst Corporation: Zoologische Anstalt der Universität Basel Dating: 27.02.1899
BRIEF OHNE UMSCHLAG Sarasin, Fritz; Sarasin, Paul Author: Sarasin, Fritz; Sarasin, Paul Recipient: Haeckel, Ernst Dating: 12.06.1899
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Rottenburg, Paul von Dating: 20.08.1899