BRIEF OHNE UMSCHLAG Altmann-Bronn, Ida Author: Altmann-Bronn, Ida Recipient: Haeckel, Ernst Dating: 13.09.1904
POSTKARTE Bölsche, Wilhelm Author: Bölsche, Wilhelm Recipient: Haeckel, Ernst Corporation: Monistenabend Berlin Dating: 27.02.1907
BRIEF OHNE UMSCHLAG Alexander, Albrecht Author: Alexander, Albrecht Recipient: Haeckel, Ernst Dating: 06.03.1917
BRIEF OHNE UMSCHLAG Scheffauer, Herman Author: Scheffauer, Herman Recipient: Haeckel, Ernst Dating: 03.10.1904
BRIEF OHNE UMSCHLAG Scheffauer, Herman Author: Scheffauer, Herman Recipient: Haeckel, Ernst Dating: 12.02.1917
TELEGRAMM Bölsche, Wilhelm; Borngräber, Otto [et al.] Author: Bölsche, Wilhelm; Borngräber, Otto [et al.] Recipient: Haeckel, Ernst Dating: 16.02.1904