Lehrbuch der vergleichenden Anatomie. 2 vols.

Vol. 2 was published in 1846; Vol. 1 in 1848. Digital facsimiles of both vols. from Biodiversity Heritage Library at this link. Siebold was the author of  Vol. 1, on invertebrates; he introduced the taxa Arthropoda and Rhizopoda, and defined the taxon Protozoa specifically for single-celled organisms. Vol. 1 was translated into English and edited with notes and additions by Waldo I. Burnet as Comparative anatomy (London: Trubner & Co.; Boston: Gould and Lincoln, 1854). Digital facsimile of the English translation from Google Books at this link.