It was necessary to follow different methods to bring natural history back into the line of true progress. The first modification of importance to the Linnæan system was that of Cuvier, who proposed a grouping of animals based upon a knowledge of their comparative anatomy. He declared that animals exhibit four types of organization, and his types were substituted for the primary groups of Linnæus. The Scale of Being.--In order to understand the bearing of Cuvier's conclusions we must take note of certain views regarding the animal kingdom that were generally accepted at the time of his writing. Between Linnæus and Cuvier there had emerged the idea that all animals, from the lowest to the highest, form a graduated series. This grouping of animals into a linear arrangement was called exposing the Scale of Being, or the Scale of Nature (_Scala Naturæ_). Buffon, Lamarck, and Bonnet were among the chief exponents of this idea. That Lamarck's connection with it was temporary has been generally overlooked. It is the usual statement in the histories of natural science, as in the _Encyclopædia Britannica_, in the History of Carus, and in Thomson's _Science of Life_, that the idea of the scale of nature found its fullest expression in Lamarck. Thomson says: "His classification (1801-1812) represents the climax of the attempt to arrange the groups of animals in linear order from lower to higher, in what was called a _scala naturæ_" (p. 14). Even so careful a writer as Richard Hertwig has expressed the matter in a similar form. Now, while Lamarck at first adopted a linear classification, it is only a partial reading of his works that will support the conclusion that he held to it. In his _Système des Animaux sans Vertèbres_, published in 1801, he arranged animals in this way; but to do credit to his discernment, it should be observed that he was the first to employ a genealogical tree and to break up the serial arrangement of animal forms. In 1809, in the second volume of his _Philosophie Zoologique_, as Packard has pointed out, he arranged animals according to their relationships, in the form of a trunk with divergent branches. This was no vague suggestion on his part, but an actual pictorial representation of the relationship between different groups of animals, as conceived by him. Although a crude attempt, it is interesting as being the first of its kind. This is so directly opposed to the idea of scale of being that we make note of the fact that Lamarck forsook that view at least twenty years before the close of his life and substituted for it that of the genealogical tree.