ANSICHTSKARTE Wiggert, Friedrich Author: Wiggert, Friedrich Recipient: Haeckel, Ernst Dating: 15.02.1909
BRIEF [O.A.] Hasse, Johann Carl Author: Hasse, Johann Carl Recipient: Haeckel, Ernst Dating: 20.12.1873
BRIEF [O.A.] Hasse, Johann Carl Author: Hasse, Johann Carl Recipient: Haeckel, Ernst Dating: 15.01.1894
BRIEF [O.A.] Hasse, Johann Carl Author: Hasse, Johann Carl Recipient: Haeckel, Ernst Dating: 19.03.1894
BRIEF [O.A.] Hasse, Johann Carl Author: Hasse, Johann Carl Recipient: Haeckel, Ernst Dating: 21.06.1894