BRIEF [O.A.] Schmidt, Heinrich Author: Schmidt, Heinrich Recipient: Haeckel, Ernst Dating: 21.10.1910
BRIEF [O.A.] Schmidt, Heinrich Author: Schmidt, Heinrich Recipient: Haeckel, Ernst Dating: 23.01.1916
BRIEF [O.A.] Schmidt, Heinrich Author: Schmidt, Heinrich Recipient: Haeckel, Ernst Dating: 30.03.1914