His Especial Service.--Nevertheless, the work of Linnæus made a lasting impression upon natural history, and we shall do well to get clearly in mind the nature of his particular service. In the first place, he brought into use the method of naming animals and plants which is employed to-day. In his _Systema Naturæ_ and in other publications he employed a means of naming every natural production in two words, and it is therefore called the binomial nomenclature. An illustration will make this clearer. Those animals which had close resemblance, like the lion, tiger, leopard, the lynx, and the cat, he united under the common generic name of _Felis_, and gave to each a particular trivial name, or specific name. Thus the name of the lion became _Felis leo_, of the tiger _Felis tigris_, of the leopard _Felis pardus_, of the cat Felis catus; and to these the modern zoölogists have added, making the Canada lynx _Felis Canadensis_, the domestic cat _Felis domesticata_, etc. In a similar way, the dog-like animals were united into a genus designated _Canis_, and the particular kinds or species became _Canis lupus_, the wolf, _Canis vulpes_, the fox, _Canis familiaris_, the common dog. This simple method took the place of the varying names applied to the same animal in different countries and local names in the same country. It recognized at once their generic likeness and their specific individuality. All animals, plants, and minerals were named according to this method. Thus there were introduced into nomenclature two groups, the genus and the species. The name of the genus was a noun, and that of the species an adjective agreeing with it. In the choice of these names Linnæus sought to express some distinguishing feature that would be suggestive of the particular animal, plant, or mineral. The trivial, or specific, names were first employed by Linnæus in 1749, and were introduced into his _Species Plantarum_ in 1753, and into the tenth edition of his _Systema Naturæ_ in 1758. We recognize Linnæus as the founder of nomenclature in natural history, and by the common consent of naturalists the date 1758 has come to be accepted as the starting-point for determining the generic and specific names of animals. The much vexed question of priority of names for animals is settled by going back to the tenth edition of his _Systema Naturæ_, while the botanists have adopted his _Species Plantarum_, 1753, as their base-line for names. As to his larger divisions of animals and plants, he recognized classes and orders. Then came genera and species. Linnæus did not use the term family in his formulæ; this convenient designation was first used and introduced in 1780 by Batch. The _Systema Naturæ_ is not a treatise on the organization of animals and plants; it is rather a catalogue of the productions of nature methodically arranged. His aim in fact was not to give full descriptions, but to make a methodical arrangement.