BRIEF OHNE UMSCHLAG Bauer, Karl; Bauer Klotilde Author: Bauer, Karl; Bauer Klotilde Recipient: Haeckel, Ernst Dating: 15.02.1909
POSTKARTE Mentz, Frida, geb. Kessel Author: Mentz, Frida, geb. Kessel Recipient: Haeckel, Ernst Dating: 15.02.1909
BRIEF [O.A.] Unbehaun, Johannes Author: Unbehaun, Johannes Recipient: Haeckel, Ernst Dating: 02.06.1909
BRIEF [O.A.] Semon, Richard W... Author: Semon, Richard W... Recipient: Haeckel, Ernst Dating: 15.02.1909