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.] Gaidetzka, Reinhard Author: Gaidetzka, Reinhard Recipient: Haeckel, Ernst Dating: 12.09.1905