BRIEF [O.A.] Gümbel, Wilhelm von Author: Gümbel, Wilhelm von Recipient: Haeckel, Ernst Dating: 10.11.1870
BRIEF [O.A.] Agassiz, Alexander Author: Agassiz, Alexander Recipient: Haeckel, Ernst Dating: 10.07.1870
BRIEF [O.A.] Engelmann, Theodor; Engelmann, Theodor Wilhelm Author: Engelmann, Theodor; Engelmann, Theodor Wilhelm Recipient: Haeckel, Ernst Dating: 14.03.1870