BRIEF [O.A.] Seidlitz, Georg [von] Author: Seidlitz, Georg [von] Recipient: Haeckel, Ernst Dating: 15.12.1868
BRIEF [O.A.] Engelmann, Theodor; Engelmann, Wilhelm Author: Engelmann, Theodor; Engelmann, Wilhelm Recipient: Haeckel, Ernst Corporation: Wilhelm Engelmann Verlagsbuchhandlung Dating: 24.03.1868
BRIEF OHNE UMSCHLAG Schenk, August Author: Schenk, August Recipient: Haeckel, Ernst Dating: 07.12.1868
BRIEF OHNE UMSCHLAG Schenk, August Author: Schenk, August Recipient: Haeckel, Ernst Dating: 29.12.1868