BRIEF [O.A.] Hentschel, Willibald Author: Hentschel, Willibald Recipient: Haeckel, Ernst Dating: 01.03.1900
BRIEF [O.A.] Hentschel, Willibald Author: Hentschel, Willibald Recipient: Haeckel, Ernst Dating: 08.07.1903
BRIEF [O.A.] Hentschel, Willibald Author: Hentschel, Willibald Recipient: Haeckel, Ernst Dating: 14.02.1904