the new ones which were constantly being discovered. But the names given were often complex and cumbersome and no uniformity existed between the systems of terminology of different authors. Also the custom of giving two or more Latin names to a species was frequently in vogue, but a binomial system, with the definite relation of the specific to the generic name, was new. The genus, which gives the clue to the natural affinities of the animal, was peculiarly Linnæus's invention.
Attempts had also been made by Ray and Klein and other advanced thinkers to form a system which should express the natural relationships of animals, but such attempts were generally not understood or followed and most authors still employed unnatural methods of arranging them. Many still followed Pliny and grouped animals according to the environmental conditions surrounding them, placing those together having similar methods of life, as land animals, freshwater animals, marine animals, flying animals, etc. Within each group the species were often arranged in alphabetical order.
Linnæus's system was very quickly accepted by the scientific world and went into universal use, and modern zoology may in a very real sense be said to begin with the year 1758.
So radical, however, was Linnæus's reform that neither the superiority of his system nor the simplicity of his terminology would probably have been sufficient thus to procure its adoption if they had not been proposed by a man of his great fame and commanding position in the world. Linnæus was considered by his contemporaries, because of his numerous and important contributions to science and his eminence as a teacher in the University of Upsala, as the greatest naturalist of all time. His importance was indicated by the phrase in vogue: Deus creavit; Linnæus disposuit.
The immediate acceptance of the Linnæan classification had the same effect upon the study of animals and plants in his day as that of Darwin's theory of natural selection had almost exactly one hundred years later. It gave a tremendous impetus to every branch of biological investigation and started a new era. Systematic zoology, morphology, physiology and experimental zoology all attracted able investigators who studied them with feverish activity. Comparative studies first became possible, as now the facts of the science were for the first time arranged in something like an orderly and natural manner, and the next generation saw the rise of the sciences of comparative anatomy, paleontology and comparative embryology, and also the first modern speculations on the blood relationships and the evolution of living things.
All these things gave a new importance to zoology and raised it from the position it had occupied of a mere annex to medicine to the dignity of an independent science.
Linnæus divided the animal kingdom into six classes: Mammalia,