BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hartmann, Eduard von Dating: 03.03.1875
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hartmann, Eduard von Dating: 07.07.1875
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hartmann, Eduard von Dating: 30.12.1875