BRIEF [O.A.] Dohrn, Carl August Author: Dohrn, Carl August Recipient: Haeckel, Ernst Dating: 05.02.1866
BRIEF [O.A.] Dallmann, Friedr... Author: Dallmann, Friedr... Recipient: Haeckel, Ernst Dating: 15.02.1904
BRIEF [O.A.] Klaucke-Blaurock, Else Author: Klaucke-Blaurock, Else Recipient: Haeckel, Ernst Dating: 21.03.1911
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Walter Dating: 10.11.1919