new." Sickness in 1812, and the disasters of the country in 1813-'14, interrupted his scientific work. In 1815 he was chosen a representative by the electors of Étampes, and performed the functions of his office with credit, till the Restoration put an end to them. Restored to science, he expounded his system in a work entitled "Philosophic Anatomique" ("Anatomical Philosophy"), the first volume of which, treating of the respiratory organs and skeletons of vertebrates, appeared in 1818. The second volume, devoted to researches on human monstrosities, was published in 1822. The dominant feature of these two volumes was the principle of unity of composition. This principle was not entirely new to science. It had been glanced at by Aristotle, Pierre Belon, Newton, Buffon, and Vicq-d'Azyr; but it remained for Geoffroy Saint-Hilaire to create a theory embodying the views which they had only mentioned sporadically.
Previous to him, naturalists, giving more particular attention to human anatomy, recognizing only forms, and regarding each new form as a new organ, had multiplied details infinitely without discovering any general law. "The first step toward rising to the ideal type of a vertebrate animal," says M. Flourens, in his eulogy before the Academy, "was to get free from every preconception in favor of human anatomy, as the only means of being able to regard the organs under their more general conditions, aside from the merely relative considerations of form, volume, and use." Geoffroy was convinced that identities can bear only upon relations, and had in this rule, which he called the principle of connections, an infallible guide through all metamorphoses, capable of unmasking the most strangely disguised affinities. Thus, whenever two parts agreed in having similar relations and dependencies, they were analogous. With this precept, Geoffroy was able to declare that the materials found in one family exist in all the others, and to proclaim his law of unity as a law of nature. In his second volume he extended the application of his principle to the formations called monstrosities, which he declared were not original anomalies, but simply cases of abnormal or of incomplete development of some particular part.
As long as the principle of unity was applied simply to vertebrates it was incontestable, and excited no contradiction; but when Geoffroy Saint-Hilaire began to extend it to invertebrates he encountered a vigorous adversary in Cuvier, whose work it had been to emphasize the distinctions between the groups which his former patron was trying to reduce to unity. When Geoffroy, in 1820, brought the articulates under his general type, Cuvier uttered words of impatience and disapproval; but, when in 1830 he proposed to include the mollusks, the long latent contention broke out. "Never," says M. Flourens, "did a more vital controversy divide adversaries more resolute, more firm, or who had by long preparation provided themselves with more resources for the combat, and (if I may say it) more learnedly prepared not to agree."