BILLET Müller, Johannes Author: Müller, Johannes Recipient: Haeckel, Ernst Dating: 1858.04.28 - 1857.03.18
BILLET Siebold, Carl Theodor Ernst von Author: Siebold, Carl Theodor Ernst von Recipient: Haeckel, Ernst Dating: 14.02.1876
BILLET Bresgen, Maximilian; Bresgen, L. Author: Bresgen, Maximilian; Bresgen, L. Recipient: Haeckel, Ernst