BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Sachsen-Altenburg, Ernst von [Herzog] Dating: 27.12.1892
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Krauseneck, Heinrich Dating: 27.12.1892
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 03.09.1892
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 17.08.1892