BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 18.06.1912
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 15.07.1912
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 10.08.1912