BRIEF [O.A.] Trautmann, Heinrich Author: Trautmann, Heinrich Recipient: Haeckel, Ernst Dating: 07.08.1903
BRIEF [O.A.] Gorzawsky, Hubert Author: Gorzawsky, Hubert Recipient: Haeckel, Ernst Dating: 23.09.1907
BRIEF [O.A.] Grube, Adolf Eduard Author: Grube, Adolf Eduard Recipient: Haeckel, Ernst Dating: 18.05.1870