BRIEFABSCHRIFT Ritter, Paul von Author: Ritter, Paul von Recipient: Haeckel, Ernst Dating: 07.01.1886
BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Eggeling, Heinrich von Dating: 03.05.1886
BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Eggeling, Heinrich Dating: 31.12.1886
BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Eggeling, Heinrich von Dating: 30.12.1886