BRIEF [O.A.] Gerstel, Gustav Author: Gerstel, Gustav Recipient: Haeckel, Ernst Corporation: Hannoversche Presse Dating: 23.03.1872
BRIEF [O.A.] Ratzel, Friedrich Author: Ratzel, Friedrich Recipient: Haeckel, Ernst Dating: 07.03.1872
BRIEF [O.A.] Ratzel, Friedrich Author: Ratzel, Friedrich Recipient: Haeckel, Ernst Dating: 24.03.1872
BRIEF [O.A.] Ratzel, Friedrich Author: Ratzel, Friedrich Recipient: Haeckel, Ernst Dating: 11.06.1872