BRIEF [O.A.] Ritter, Paul von Author: Ritter, Paul von Recipient: Haeckel, Ernst Corporation: Bibliographisches Institut Dating: 31.10.1904
BRIEF [O.A.] Bunge, Gustav von Author: Bunge, Gustav von Recipient: Haeckel, Ernst Dating: 03.10.1904
BRIEF [O.A.] Bunge, Gustav von Author: Bunge, Gustav von Recipient: Haeckel, Ernst Dating: 28.12.1904
BRIEF [O.A.] Zschokke, Friedrich Author: Zschokke, Friedrich Recipient: Haeckel, Ernst Corporation: Zoologische Anstalt der Universität Basel Dating: 15.02.1904