BRIEF [O.A.] Haeckel, Karl; Sethe, Bertha Author: Haeckel, Karl; Sethe, Bertha Recipient: Haeckel, Ernst Dating: 10.08.1894
BRIEF [O.A.] Haeckel, Karl; Haeckel, Siegfried Author: Haeckel, Karl; Haeckel, Siegfried Recipient: Haeckel, Ernst Dating: 13.06.1894