BRIEF [O.A.] Verbeek, R... W... M... Author: Verbeek, R... W... M... Recipient: Haeckel, Ernst Dating: 19.10.1900
BRIEF [O.A.] Verbeek, R... W... M... Author: Verbeek, R... W... M... Recipient: Haeckel, Ernst Dating: 09.12.1900
BRIEF [O.A.] Verbeek, R... W... M... Author: Verbeek, R... W... M... Recipient: Haeckel, Ernst Dating: 30.01.1901
BRIEF [O.A.] Verbeek, R... W... M... Author: Verbeek, R... W... M... Recipient: Haeckel, Ernst Dating: 20.12.1900