BRIEF [O.A.] Schultz, Ehrenfried Author: Schultz, Ehrenfried Recipient: Haeckel, Ernst Dating: 26.07.1903
BRIEF [O.A.] Recipient: Haeckel, Ernst Corporation: Verlagsbuchhandlung Erich Hecht Dating: 01.08.1903
BRIEF [O.A.] Trautmann, Heinrich Author: Trautmann, Heinrich Recipient: Haeckel, Ernst Dating: 07.08.1903
BRIEF [O.A.] Szarlitt, Bernard Author: Szarlitt, Bernard Recipient: Haeckel, Ernst Dating: 18.03.1903
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 09.08.1903