BRIEF [O.A.] Leemann, J... A... Author: Leemann, J... A... Recipient: Haeckel, Ernst Dating: 14.09.1912
BRIEF [O.A.] Leemann, J... A... Author: Leemann, J... A... Recipient: Haeckel, Ernst Dating: 20.09.1912
BRIEF [O.A.] Leemann, J... A... Author: Leemann, J... A... Recipient: Haeckel, Ernst Dating: 10.05.1913