TELEGRAMM Engelmann, Theodor Wilhelm Author: Engelmann, Theodor Wilhelm Recipient: Haeckel, Ernst Dating: 16.02.1904
BRIEF OHNE UMSCHLAG Engelmann, Theodor Wilhelm Author: Engelmann, Theodor Wilhelm Recipient: Haeckel, Ernst Dating: 17.10.1904
BRIEFABSCHRIFT Engelmann, Theodor Wilhelm Author: Engelmann, Theodor Wilhelm Recipient: Watts, Charles Corporation: Wilhelm Engelmann Verlagsbuchhandlung Dating: 18.04.1904