BRIEF [O.A.] Retowski, Alexander Author: Retowski, Alexander Recipient: Haeckel, Ernst Dating: 31.01.1905
BRIEF [O.A.] Krupp, Clara (geb. Petersen) Author: Krupp, Clara (geb. Petersen) Recipient: Haeckel, Ernst Dating: 12.01.1917
BRIEF [O.A.] Krupp, Clara (geb. Petersen) Author: Krupp, Clara (geb. Petersen) Recipient: Haeckel, Ernst Dating: 15.02.1914
BRIEF [O.A.] Krupp, Clara (geb. Petersen) Author: Krupp, Clara (geb. Petersen) Recipient: Haeckel, Ernst Dating: 15.02.1891
BRIEF [O.A.] Krupp, Clara (geb. Petersen) Author: Krupp, Clara (geb. Petersen) Recipient: Haeckel, Ernst Dating: 24.06.????
