The principle of priority states simply that the earliest name applied properly to a taxon of animals is the correct scientific name, with the date of publication determined by the stated date on the publication or by other means if that information is not reliable. Priority now dates from 1 January 1758, the date fixed for the publication of the tenth edition of Linnaeus’s Systema Naturae. If two species or two genera are merged for whatever reason, the correct name is the earliest one proposed. If investigation indicates that a species or a genus should be divided into two, then the former name remains with the type and a new name must be proposed for the other taxon if a name does not already exist for it. Many changes in zoological nomenclature resulted from the application of priority, especially when sorting out the work of the early taxonomists, and major changes stemmed from the decision to change the beginning date for zoological nomenclature from the twelfth edition (1766) of Linnaeus to the earlier tenth edition (1758).