BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hellwald, Friedrich von Dating: 07.02.1875
BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hellwald, Friedrich von Dating: 13.02.1875
BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hellwald, Friedrich von Dating: 14.06.1875
BRIEFABSCHRIFT Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hellwald, Friedrich von Dating: 20.12.1875