BRIEF [O.A.] Osterwald, Wilhelm Author: Osterwald, Wilhelm Recipient: Haeckel, Carl Gottlob Dating: 06.03.1852
BRIEF [O.A.] Allmers, Hermann Author: Allmers, Hermann Recipient: Haeckel, Carl Gottlob Dating: 11.05.1860
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Carl Gottlob Dating: 10.03.1866