BRIEF [O.A.] Haberlandt, Gottlieb Author: Haberlandt, Gottlieb Recipient: Haeckel, Ernst Dating: 14.02.1904
BRIEF [O.A.] Tóth von Felseö-Szopor, Marie Author: Tóth von Felseö-Szopor, Marie Recipient: Haeckel, Ernst Dating: 14.02.1904
BRIEF [O.A.] Pretzlik, Anton Author: Pretzlik, Anton Recipient: Haeckel, Ernst Corporation: Haeckelgemeinde Salzburg Dating: 17.05.1904