BRIEF [O.A.] Föhr, Karl Ferdinand Author: Föhr, Karl Ferdinand Recipient: Haeckel, Ernst Dating: 12.12.1877
BRIEF [O.A.] Hildebrand, Marie Author: Hildebrand, Marie Recipient: Haeckel, Ernst Dating: 14.02.1894
BRIEF [O.A.] Cotta, Bernhard von Author: Cotta, Bernhard von Recipient: Haeckel, Ernst Dating: 18.10.1868
BRIEF [O.A.] Cotta, Bernhard von Author: Cotta, Bernhard von Recipient: Haeckel, Ernst Dating: 20.10.1870