BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Uslar-Gleichen, Bernhard von Dating: 05.09.1910
BRIEF [O.A.] Grimaldi, Vincento Author: Grimaldi, Vincento Recipient: Haeckel, Ernst Corporation: Associazione di Publica Assistenza Dating: 13.04.1911
BRIEF [O.A.] Donvito, Eduardo Author: Donvito, Eduardo Recipient: Haeckel, Ernst Corporation: Il Pubblicista - La Gioventù Dating: 02.04.1912