BRIEF [O.A.] Gerhardt, Dietrich Author: Gerhardt, Dietrich Recipient: Haeckel, Ernst Dating: 01.08.1883
BRIEF [O.A.] Gerhardt, Dietrich Author: Gerhardt, Dietrich Recipient: Haeckel, Ernst Dating: 15.02.1884
BRIEF [O.A.] Rindfleisch, E... Author: Rindfleisch, E... Recipient: Haeckel, Ernst Dating: 21.07.1881
BRIEF [O.A.] Recklinghausen, Friedrich Daniel Author: Recklinghausen, Friedrich Daniel Recipient: Haeckel, Ernst Dating: 12.03.1868