BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hertwig, Richard Dating: 22.12.1906
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hertwig, Richard Dating: 11.01.1906
BRIEF MIT UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hintze, Wilhelmine Dating: 22.03.1906