BRIEF OHNE UMSCHLAG Doubleday, H. S. Author: Doubleday, H. S. Recipient: Haeckel, Ernst Dating: 20.10.1907
BRIEF OHNE UMSCHLAG Doubleday, H. S. Author: Doubleday, H. S. Recipient: Haeckel, Ernst Dating: 22.03.1909
BRIEF OHNE UMSCHLAG Malmer, Hermann Author: Malmer, Hermann Recipient: Haeckel, Ernst Dating: 28.12.1908
BRIEF OHNE UMSCHLAG Witton, Henry Buckingham Author: Witton, Henry Buckingham Recipient: Haeckel, Ernst Dating: 08.11.1909