BRIEF [O.A.] Haltermann, Hermann Author: Haltermann, Hermann Recipient: Haeckel, Ernst Dating: 08.04.1869
BRIEF [O.A.] Haltermann, Hermann Author: Haltermann, Hermann Recipient: Haeckel, Ernst Dating: 08.05.1871
BRIEF [O.A.] Haltermann, Hermann Author: Haltermann, Hermann Recipient: Haeckel, Ernst Dating: 12.05.1871