BRIEFABSCHRIFT Ritter, Paul von Author: Ritter, Paul von Recipient: Haeckel, Ernst Dating: 07.01.1886
BRIEF [O.A.] Ritter, Paul von Author: Ritter, Paul von Recipient: Eggeling, Heinrich von Dating: 05.12.1901
BRIEF [O.A.] Ritter, Paul von Author: Ritter, Paul von Recipient: Eggeling, Heinrich von Dating: 06.12.1901