POSTKARTE Osborn, Henry Fairfield Author: Osborn, Henry Fairfield Recipient: Haeckel, Ernst Dating: ??.??.1906
BRIEF [O.A.] Gregory, William K... Author: Gregory, William K... Recipient: Haeckel, Ernst Corporation: American Museum of Natural History Dating: 23.01.1914
BRIEF OHNE UMSCHLAG Recipient: Gruyter, Walter de Corporation: Dodd, Mead and Company Publishers Dating: 27.12.1915
BRIEF OHNE UMSCHLAG Calenda, Vincent D. Author: Calenda, Vincent D. Recipient: Haeckel, Ernst Dating: 25.06.1913
BRIEF OHNE UMSCHLAG Calenda, Vincent D. Author: Calenda, Vincent D. Recipient: Haeckel, Ernst Dating: 22.08.1913
POSTKARTE Calenda, Vincent D. Author: Calenda, Vincent D. Recipient: Haeckel, Ernst Dating: 24.12.1913
BRIEF OHNE UMSCHLAG Calenda, Vincent D. Author: Calenda, Vincent D. Recipient: Haeckel, Ernst Dating: 21.01.1914
BRIEF OHNE UMSCHLAG Calenda, Vincent D. Author: Calenda, Vincent D. Recipient: Haeckel, Ernst Dating: 31.01.1914