Lithograph by Ernst Haeckel and Adolf Giltsch
This is a figure on plate 51, one of the 100 pop science biology illustrations that were published from 1899 – 1904 in Leipzig by Ernst Haeckel through Verlag des Bibliographischen Instituts, Giltsch Lithografische Anstalt Jena.
We've scanned the original lithography, you can download it by clicking on the picture.