BRIEF MIT UMSCHLAG Sickels, N. D. Author: Sickels, N. D. Recipient: Haeckel, Ernst Dating: 20.08.1915
BRIEF OHNE UMSCHLAG Darling, Ernest Willing Author: Darling, Ernest Willing Recipient: Haeckel, Ernst Dating: 22.09.1913
BRIEF MIT UMSCHLAG Darling, Ernest Willing Author: Darling, Ernest Willing Recipient: Haeckel, Ernst Dating: 01.06.1914
POSTKARTE Darling, Ernest Willing Author: Darling, Ernest Willing Recipient: Haeckel, Ernst Dating: 04.11.1915
BRIEF [O.A.] Cless, Alfred Martin Author: Cless, Alfred Martin Recipient: Haeckel, Ernst Dating: 24.03.1900
BRIEF [O.A.] Kellogg, Vernon Lyman Author: Kellogg, Vernon Lyman Recipient: Haeckel, Ernst Corporation: Leland Stanford University Dating: ??.12.1894
BRIEF [O.A.] Sanders, Frederic W... Author: Sanders, Frederic W... Recipient: Haeckel, Ernst Dating: 22.07.1914