BRIEF [O.A.] Kayser, J... H... Author: Kayser, J... H... Recipient: Haeckel, Ernst Dating: 10.02.1914
BRIEF [O.A.] Rossbach, Rich... Author: Rossbach, Rich... Recipient: Haeckel, Ernst Dating: 16.02.1914
ANSICHTSKARTE Jung, Rudolf Heinrich Author: Jung, Rudolf Heinrich Recipient: Haeckel, Ernst Dating: 15.02.1914
TELEGRAMM Mengden, Nicolai Baron von Author: Mengden, Nicolai Baron von Recipient: Haeckel, Ernst Dating: 16.02.1914