BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 09.08.1903
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 29.05.1903
BRIEF [O.A.] Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Ernst Dating: 15.02.1903
BRIEF OHNE UMSCHLAG Haeckel, Heinrich Author: Haeckel, Heinrich Recipient: Haeckel, Julius Dating: 24.02.1903