BRIEF [O.A.] Forsberg, Hjalmar Author: Forsberg, Hjalmar Recipient: Haeckel, Ernst Dating: 25.07.1911
BRIEF [O.A.] Brückner, Hermann Author: Brückner, Hermann Recipient: Haeckel, Ernst Dating: 20.05.1911
BRIEF [O.A.] Reinicke, Emanuel Author: Reinicke, Emanuel Recipient: Haeckel, Ernst Corporation: Wilhelm Engelmann Verlagsbuchhandlung Dating: 04.01.1911
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Leipziger Freie Studentenschaft Dating: 05.01.1911