BRIEF [O.A.] Hentschel, Willibald Author: Hentschel, Willibald Recipient: Haeckel, Ernst Dating: 04.01.1911
BRIEF [O.A.] Hentschel, Willibald Author: Hentschel, Willibald Recipient: Haeckel, Ernst Dating: 31.01.1911
BRIEF [O.A.] Hentschel, Willibald Author: Hentschel, Willibald Recipient: Haeckel, Ernst Dating: 1911.??.?? [?]