BRIEF OHNE UMSCHLAG Sokolowsky, Alexander Author: Sokolowsky, Alexander Recipient: Haeckel, Ernst Dating: 13.07.1908
BRIEF OHNE UMSCHLAG Keller, Conrad Author: Keller, Conrad Recipient: Haeckel, Ernst Dating: 19.07.1908
BRIEF OHNE UMSCHLAG Burckhardt, Fritz Author: Burckhardt, Fritz Recipient: Haeckel, Ernst Dating: 16.01.1908