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ter, he was b. 23 May, 1707, at Rashult in the south of Sweden; d. 177S. In 1741 he was made professor of medicine, and a little later of botany, in the Uni- versity of Upsala, of which he was an alumnus. His main work, "Systenia naturae", was published for the first time in 173.5. Its complete edition is the 17th, which appeared ten years after the author's death. As its title indicates, the work is essentially a system of classification, comprising all the minerals, plants, and animals known in Linneeus' time, arranged according to classes, genera, and species. The value of this classification is mainly due to the precision of its new nomenclature. According to this "binomial" nomenclature each plant or ani- mal received a generic and a specific name, as, for instance, Felis catus and Felis Ico, indicating at once the systematic relation of the organism. Linnseus exercised a vast influence upon the biologists of his time and considerably furtliered the collection of numerous morphological facts which served the great scientists of the following century as the fotmdation of their various theories.

To the Frenchman, Marie-Frangois-Xavier Bichat (1771-1S02), morphology owes its position as a logi- cally co-ordinated science. Bichat was the first to introduce into biology the distinction between systems composed of heterogeneous organs and systems composed of homogeneous tissues. In a system of the former class all the organs serve some particular group of vital functions, as, for instance, the digestive system. The latter class of systems comprises all tissues which have an identical struc- ture, as, for instance, the system of secretion. To the scientific principle estalalished by Bichat two others were soon added which are of still greater importance in morphologj^. These are the laws of correlation and of homology of organs. According to the law of correlation there is a certain inter- dependence of all the organs of an animal, so that from the peculiar structure of one organ we may conclude as to the structure of most other organs. The law of the homology of organs maintains that all organs constructed according to the same pattern must have similar functions. But, as the same function is not necessarily bound to the same struc- ture (e. g., the function of breathing, which may be accomplished by gills as well as by lungs), the law was complemented by the principle of the analogy of organs.

These highly suggestive laws were chiefly estab- lishea by George iSagobert Cuvier — like Linnipus, a devout Protestant — who was b. in 1769 at Mompel- gardt, Wiirtemberg, and died, a peer of France, in 1832. His chief works were ■nTitten when he was professor of comparative anatomy at the Jardin des Plantes in Paris. In Cuvier's mind originated the celebrated theory of types, which was established in the year 1812. Taking the principle for the new division of the animal kingdom from the peculiar organization of the animal, Cuvier comprises the classes of mammals, birds, and reptiles under the name of vertebrates, which had shortly before been introduced by Lamarck. The other cla.sses of animals were divided into three provinces (embranchemcntx), the molluscs, the articulates, and the radiates. As the doctrine of the constancy of species, Cuvier's system was opposed by Etienne-GeoiTroy Saint- Hilaire (1722-1844), who emphasized the universal unity of the plan of structure pervading the animal kingdom. Cuvier also made an extensive study of the petrified organisms of prehistoric ages, and thus became the founder of the science of palaeontology. Cuvier's system was further developed by C. E. von Baer (1792-1876), who discovered the mammalian ovum, and through his studies of the development of the chick laid the foundations to the science of comparative morphogeny.

During the same period of the eighteenth century the science of physiology made considerable progress through the work of Boerhaave, Stahl, and Haller. Hermann Boerhaave (1668-1738) was for a long time professor of medicine at Leyden. He was an adherent neither of the extreme chemical nor of the extreme physical school, but tried to reconcile both doctrines. His main work, "Institutiones medicae. was published in 1708. A similar position as to the causes of physiological phenomena was assumed by George Ernest von Stahl (1660-1734), famous in the annals of chemistry for his phlogiston theory. Stahl's views were embraced by a pupil of Boerhaave, Albrecht von Haller (1708-77), who united in his voluminous work, "Elementa Physiologiae corporis humani", all the theories and discoveries known to his time, and grouped them in a new manner, so that his book may be called tlie first modern text- book of physiology. About the time when Haller died Antoine-Laurent Lavoisier (who was guillotined by the Convention in 1794) added to the sura of physiological knowledge by solving the problem of oxidation and respiration.

Fourth period. — Meanwhile another important discovery had been made which gradually inaugu- rated the fourth and most splendid period of biologj-, the chief activities of which centre about the struc- ture and functions of the cell, and about individual and specific evolution. During the same period im- mense progress has been made in bionomics, palaeon- tology, morphology, physiology, and, indeed, all biological sciences. The fact has already been al- luded to that, towards the close of the sixteenth century, a native of Holland, Zachary Janssen, had invented the microscope, which, after it had been considerably improved by Francesco Fontana, of Naples, and Cornelis van Drebbel, of Holland, was used by Malpighi, Jan Swammerdam (1627-80) of Amsterdam, the Englishmen Hooke and Grew, and by Antonius von Leeuwenhoek (1632-1723), the famous discoverer of the infusorians. Robert Hooke (1635- 1702) was the first to represent in his " Micrographia " a group of cells which he had disco\'ered with his microscope in plants; but Malpighi and Grew are generally credited ^ith having discovered the cell. About a century later Kaspar Friedrich Wolff pub- lished his important "Theoria generationis " (1759), which clearly shows that he must have observed cells in plants as well as in animals. All this, however, was but preliminary; the new era in biologj- was fairly opened only when, in the years 1S3S and 1839, the botanist Sclileiden and, especially, the zoologist Schwann, established the first theory of the cell: that the cell ix the ultimate structural and functional unit of life. Theodor Schwann was b. at Neuss, near Cologne, in 1810 and became professor of anatomy at Louvain in 1839, and at Liege in 1848, and died in 1882. He was a faithful Catholic throughout his life. Schwann's theorj- was further developed by F. Ley- dig (1S57), by M. Schultze (1861), and by a host of such eminent scientists of the present generation, as J. Reinke, O. Hertwig, Waldeyer, Edmund B. Wilson, and many others. The name histology (see definitions at beginning of this article) was in- troduced by K. Meyer in 1819, whilst John B. Carney, who died in 1899 as a Catholic priest and professor at Louvain, is the acknowledged author and able promoter of ciftology.

Together with cytology there came into prominence the science of ontogeny which has led many biologists of to-day back to a vitalistic conception of the phenomena of life. This science it was that suggested E. Hackel's biogenetic law, to which it also gave the deathblow. According to Hackel's theory, on- togeny is said to be a short and rapid repetition of phylogeny. The first to trace the entire development of all the tissues from the germ cells was Schwann.