POSTKARTE Porter, Carlos Emilio Author: Porter, Carlos Emilio Recipient: Haeckel, Ernst Dating: 15.10.1910
BRIEF OHNE UMSCHLAG Strasburger, Eduard Author: Strasburger, Eduard Recipient: Haeckel, Ernst Dating: 06.04.1910
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Rottenburg, Paul von Dating: 03.04.1910
BRIEF OHNE UMSCHLAG Haeckel, Ernst Author: Haeckel, Ernst Recipient: Rottenburg, Paul von Dating: 11.04.1910
ANSICHTSKARTE Haeckel, Ernst Author: Haeckel, Ernst Recipient: Hintze [Altwein], Wilhelmine Dating: 22.04.1910