BRIEF [O.A.] Rothe, Karl Author: Rothe, Karl Recipient: Haeckel, Ernst Corporation: Großherzogliches S. Staatsministerium, Department des Kultus. St. 18 Dating: 06.03.1907
BRIEF [O.A.] Van de Velde-Sethe, Maria Author: Van de Velde-Sethe, Maria Recipient: Haeckel, Ernst Dating: 28.06.1907
BRIEF [O.A.] Steman, Friedrich Author: Steman, Friedrich Recipient: Haeckel, Ernst Dating: 13.04.1907
BRIEF [O.A.] Wilhelm Ernst [Erzherzog von Sachsen-Weimar] Author: Wilhelm Ernst [Erzherzog von Sachsen-Weimar] Recipient: Haeckel, Ernst Dating: 06.03.1907