BRIEF [O.A.] Schmidt, Heinrich Author: Schmidt, Heinrich Recipient: Haeckel, Ernst Dating: 05.11.1907
BRIEF [O.A.] Schmidt, Heinrich Author: Schmidt, Heinrich Recipient: Haeckel, Ernst Dating: 17.01.1907
BRIEF OHNE UMSCHLAG Schmidt, Heinrich Author: Schmidt, Heinrich Recipient: Haeckel, Ernst Dating: 24.09.1907