ANSICHTSKARTE Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 03.03.1910
TELEGRAMM Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 16.02.1910
BRIEF [O.A.] Zentella, Arcadio Author: Zentella, Arcadio Recipient: Haeckel, Ernst Corporation: Instrucción Pública Dating: 08.02.1910