BRIEF OHNE UMSCHLAG Bleek, Theodor Author: Bleek, Theodor Recipient: Haeckel, Ernst Dating: 12.08.1873
BRIEF [O.A.] Frenkel, Ferdinand Author: Frenkel, Ferdinand Recipient: Haeckel, Ernst Dating: 14.12.1873
BRIEF OHNE UMSCHLAG Müller, Hermann Author: Müller, Hermann Recipient: Haeckel, Ernst Dating: 28.02.1873
BRIEF OHNE UMSCHLAG Müller, Hermann Author: Müller, Hermann Recipient: Haeckel, Ernst Dating: 05.12.1873
BRIEF OHNE UMSCHLAG Müller, Hermann Author: Müller, Hermann Recipient: Haeckel, Ernst Dating: 13.12.1873