BRIEF [O.A.] Büchner, E. Author: Büchner, E. Recipient: Haeckel, Ernst Corporation: Deutsche Verlags-Anstalt Dating: 04.07.1891
BRIEF OHNE UMSCHLAG Loewenstein, Adolf; Goßrau, Carl Author: Loewenstein, Adolf; Goßrau, Carl Recipient: Haeckel, Ernst Corporation: Deutsche Verlags-Anstalt Dating: 14.04.1906
BRIEF [O.A.] Daiber, Albert Ludwig Author: Daiber, Albert Ludwig Recipient: Haeckel, Ernst Dating: 18.09.1905
BRIEF [O.A.] Daiber, Albert Ludwig Author: Daiber, Albert Ludwig Recipient: Haeckel, Ernst Dating: 28.09.1905
BRIEF [O.A.] Daiber, Albert Ludwig Author: Daiber, Albert Ludwig Recipient: Haeckel, Ernst Dating: 29.10.1905
BRIEF OHNE UMSCHLAG Kilpper, Gustav Author: Kilpper, Gustav Recipient: Haeckel, Ernst Corporation: Deutsche Verlags-Anstalt Stuttgart Dating: 23.10.1910