BRIEF [O.A.] Trefflich, Walter Author: Trefflich, Walter Recipient: Haeckel, Ernst Dating: ??.??.1913
BRIEF [O.A.] Trefflich, Walter Author: Trefflich, Walter Recipient: Haeckel, Ernst Dating: 30.03.1913
BRIEF [O.A.] Trefflich, Walter Author: Trefflich, Walter Recipient: Haeckel, Ernst Dating: 15.10.1913