BRIEF [O.A.] Tischendorf, Marie Author: Tischendorf, Marie Recipient: Haeckel, Ernst Dating: 17.02.1904
BRIEF OHNE UMSCHLAG Vogel, Richard; Zilich, W. Author: Vogel, Richard; Zilich, W. Recipient: Haeckel, Ernst Dating: 05.12.1903
BRIEF OHNE UMSCHLAG Duisberg, Carl Author: Duisberg, Carl Recipient: Haeckel, Ernst Dating: 16.07.1908
BRIEF OHNE UMSCHLAG Strutz, Edmund Author: Strutz, Edmund Recipient: Haeckel, Ernst Dating: 14.02.1909
BRIEF [O.A.] Duisberg, Carl Author: Duisberg, Carl Recipient: Haeckel, Ernst Corporation: Farbenfabriken vormals Friedrich Bayer & Co. Dating: 28.03.1892