BRIEF [O.A.] Franco, Isidoro de Author: Franco, Isidoro de Recipient: Haeckel, Ernst Dating: 08.12.1906
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BRIEF [O.A.] Franco, Isidoro de Author: Franco, Isidoro de Recipient: Haeckel, Ernst Dating: 21.01.1908
BRIEF [O.A.] Franco, Isidoro de Author: Franco, Isidoro de Recipient: Haeckel, Ernst Dating: ??.??.1908
BRIEF [O.A.] Franco, Isidoro de Author: Franco, Isidoro de Recipient: Haeckel, Ernst Dating: 28.02.1914