BRIEF [O.A.] Poritzky, J... E... Author: Poritzky, J... E... Recipient: Haeckel, Ernst Dating: 10.05.1900
BRIEF [O.A.] Poritzky, J... E... Author: Poritzky, J... E... Recipient: Haeckel, Ernst Dating: 29.06.1900
BRIEF [O.A.] Poritzky, J... E... Author: Poritzky, J... E... Recipient: Haeckel, Ernst Dating: 08.07.1900
BRIEF [O.A.] Poritzky, J... E... Author: Poritzky, J... E... Recipient: Haeckel, Ernst Dating: 03.08.1900
BRIEF [O.A.] Poritzky, J... E... Author: Poritzky, J... E... Recipient: Haeckel, Ernst Dating: 11.08.1900