BRIEF [O.A.] Harting, (Pieter) Paul [?] Author: Harting, (Pieter) Paul [?] Recipient: Haeckel, Ernst Dating: 11.01.1869
BRIEF [O.A.] Harting, (Pieter) Paul [?] Author: Harting, (Pieter) Paul [?] Recipient: Haeckel, Ernst Dating: 26.06.1869
BRIEF [O.A.] Nooten, N. van Author: Nooten, N. van Recipient: Haeckel, Ernst Corporation: Provinciaal-Utrechtsch Genootschap van Kunsten en Wetenschappen Dating: 13.10.1869