BRIEF [O.A.] Baumann, Friedrich Author: Baumann, Friedrich Recipient: Haeckel, Ernst Dating: 18.01.1912
BRIEF [O.A.] Baumann, Friedrich Author: Baumann, Friedrich Recipient: Haeckel, Ernst Dating: 28.09.1914
BRIEF [O.A.] Barnard, William Stebbins Author: Barnard, William Stebbins Recipient: Haeckel, Ernst Dating: 23.06.1874