Before 1758, most biological catalogues had used polynomial names for the taxa included, including earlier editions of Systema Naturae. The first work to consistently apply binomial nomenclature across the animal kingdom was the 10th edition of Systema Naturae. The International Commission on Zoological Nomenclature therefore chose 1 January 1758 as the "starting point" for zoological nomenclature, and asserted that the 10th edition of Systema Naturae was to be treated as if published on that date. Names published before that date are unavailable, even if they would otherwise satisfy the rules. The only work which takes priority over the 10th edition is Carl Alexander Clerck's Svenska Spindlar or Aranei Suecici, which was published in 1757, but is also to be treated as if published on January 1, 1758.
During Linnaeus' lifetime, Systema Naturae was under continuous revision. Progress was incorporated into new and ever-expanding editions; for example, in his 1st edition (1735), whales and manatees were originally classified as species of fish (as was thought to be the case then), but in the 10th edition they were moved into the mammal class.
The Animal Kingdom (as described by Linnaeus): Animals enjoy sensation by means of a living organization, animated by a medullary substance; perception by nerves; and motion by the exertion of the will. They have members for the different purposes of life; organs for their different senses; and faculties (or powers) for the application of their different perceptions. They all originate from an egg. Their external and internal structure; their comparative anatomy, habits, instincts, and various relations to each other, are detailed in authors who prosessedly treat on their subjects.
The list has been broken down into the original six classes Linnaeus described for animals; Mammalia, Aves, Amphibia, Pisces, Insecta, & Vermes. These classes were ultimately created by studying the internal anatomy, as seen in his key: