BRIEF [O.A.] Griessmann, Bruno Author: Griessmann, Bruno Recipient: Haeckel, Ernst Dating: 19.08.1907
BRIEF [O.A.] Grimme, Emil A... Author: Grimme, Emil A... Recipient: Haeckel, Ernst Dating: 11.03.1915
BRIEF [O.A.] Eber, Almi Author: Eber, Almi Recipient: Haeckel, Ernst Corporation: Verein Merkur Dating: 05.06.1883
BRIEF [O.A.] Einstein, Leopold Author: Einstein, Leopold Recipient: Haeckel, Ernst Dating: 13.01.1882