Summary.--In reviewing the rise of scientific natural history, we observe a steady development from the time of the _Physiologus_, first through a return to Aristotle, and through gradual additions to his observations, notably by Gesner, and then the striking improvements due to Ray and Linnæus. We may speak of the latter two as the founders of systematic botany and zoölogy. But the system left by Linnæus was artificial, and the greatest obvious need was to convert it into a natural system founded upon a knowledge of the structure and the development of living organisms. This was begun by Cuvier and Von Baer, and was continued especially by Von Siebold and Leuckart. To this has been added the study of habits, breeding, and adaptations of organisms, a study which has given to natural history much greater importance than if it stood merely for the systematic classification of animals and plants. Tabular View of Classifications.--A table showing the primary groups of Linnæus, Cuvier, Von Siebold, and Leuckart will be helpful in picturing to the mind the modifications made in the classification of animals. Such a table is given on the following page. L. Agassiz, in his famous essay on Classification, reviews in the most scholarly way the various systems of classification. One peculiar feature of Agassiz's philosophy was his adherence to the dogma of the fixity of species. The same year that his essay referred to was published (1859) appeared Darwin's _Origin of Species_. Agassiz, however, was never able to accept the idea, of the transformations of species. Linnæus Cuvier Von Siebold Leuckart Mammalia Vertebrata Vertebrata Vertebrata (Embracing five (Embracing five (Five classes.) Aves classes: Mammalia, classes.) Aves, Reptilia, Amphibia Batrachia, Pisces.) Pisces Insecta Mollusca Mollusca Mollusca (Including Crustacea, {Arthropoda etc.) Articulata {Vermes Arthropoda Vermes Vermes {Zoöphyta {Echinoderma (Including Radiata {Coelenterata Mollusca and all {Protozoa Protozoa lower forms.) Steps in Biological Progress from Linnæus to Darwin