BRIEF [O.A.] Vosmaer, G... C. J. Author: Vosmaer, G... C. J. Recipient: Haeckel, Ernst Dating: 19.12.1889
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Nederlansche Dierkundige Vereeniging (Netherland Zoological Society) Dating: 25.09.1894
BRIEF [O.A.] Harting, (Pieter) Paul [?] Author: Harting, (Pieter) Paul [?] Recipient: Haeckel, Ernst Dating: 07.07.1868
BRIEF [O.A.] Harting, (Pieter) Paul [?] Author: Harting, (Pieter) Paul [?] Recipient: Haeckel, Ernst Dating: 11.01.1869
