BRIEF [O.A.] Ihle, J... E... W... Author: Ihle, J... E... W... Recipient: Haeckel, Ernst Dating: 18.08.1897
BRIEF OHNE UMSCHLAG Engelmann, Theodor Wilhelm Author: Engelmann, Theodor Wilhelm Recipient: Haeckel, Ernst Dating: 02.07.1897
BRIEF OHNE UMSCHLAG Martin, Karl Author: Martin, Karl Recipient: Haeckel, Ernst Corporation: `s Rijks Geologisch-Mineralogisch Museum Dating: 08.07.1897