BRIEF [O.A.] Traill, Geo... Will... Author: Traill, Geo... Will... Recipient: Haeckel, Ernst Dating: 02.10.1886
BRIEF [O.A.] Traquair, R... H... Author: Traquair, R... H... Recipient: Haeckel, Ernst Dating: 14.02.1892
BRIEF [O.A.] Haeckel, Ernst Author: Haeckel, Ernst Recipient: Krauseneck, Heinrich Dating: 25.08.1892