BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Haeckel, Walter; Haeckel, Agnes Dating: 09.10.1889
POSTKARTE Reichmann, Carlo Augusto Author: Reichmann, Carlo Augusto Recipient: Haeckel, Ernst Dating: 31.12.1889
BRIEF OHNE UMSCHLAG Gegenbaur, Carl Author: Gegenbaur, Carl Recipient: Haeckel, Ernst Dating: 10.04.1889