BRIEF [O.A.] Baumann, Friedrich Author: Baumann, Friedrich Recipient: Haeckel, Ernst Dating: 18.01.1912
BRIEF [O.A.] Carus, Paul Author: Carus, Paul Recipient: Haeckel, Ernst Corporation: The Open Court Publishing Company Dating: 15.02.1912
BRIEF [O.A.] Kenney, C... T... Author: Kenney, C... T... Recipient: Haeckel, Ernst Dating: 31.07.1912