Page:The New International Encyclopædia 1st ed. v. 04.djvu/930

* CLASSIFICATION OF ANIMALS. 820 CLASSIFICATION OF ANIMALS. etc., characteristic of methods of life, are of the kind of characters used in judgin|; of family limits. Thus, the prime family distinction of the cats (Felida-) is the ariangcment for re- tracting the claws, which shar])ly dctines them as a group from the dog*, on one hand, and tlie civets on the other; but the oliceta is able to retract its claws only partly, and this fact, in connection with other distinflive features, causes tlie animal to be placed in a genus separate from Felis. Order. — Several related families may fall to- gether, by the possession in common of char- acters denied to others, into a larger category known as an order. A familiar example is the order Carnivora, embracing the families of cats, dogs, civets, weasels, bears, etc., Ijecause all these exhibit an organization developed along lines of ditl'erentiation from other mammals, tending to fit them to prey upon other animals and digest a flesh diet. The various lines and degrees of specialization are recognized by sub- ordinate groupings in families and genera. Class. — Groups of orders are found to agree in certain very general and fundamental charac- teristics of organization, such as having six legs or eight legs; the producticm, by the skin, of hair, feathers, or scales; the integument being leathery or calcareous — and so on; and such groups form the next larger category, called a class. Even here, however, there is large room for difference of opinion as to limits; and, in «ome classes, an intermediate category called subclass seems necessary, as in the case of the prime division of the class Mammalia into mono- dclphic and didelphic. or of the class Cephalo- poda into dibranchiate and tetrabranchiate. The same difficulty has led to naming groups of in- termediate rank elsewhere — such as superfami- lies, subfamilies, subgenera, etc. Phyla. — Classes combine into several grand divisions of the animal kingdom, called sub- kingdoms, or phyla, by having in common a single or a few characteristics so broad and an- cestral that they are spoken of as 'plan of struc- ture.' Thus, all the mammals, birds, reptiles, amphibians, and fishes, together with several lowly representatives, such as the ascidians, arc imited by a single characteristic of structure possessed by no other animals — the presence of a backbone, or its essential equivalent, the noto- ohord. This character is so wide-reaching and fundamental that it springs from the very root of the phy'ogenetic tree, and is of prime impor- tance. By similar broad and fundamental 'plans of structure' are the other phyla of the twelve now recognized by most zoologists characterized. Their origin is lost to view in the mists of primeval time, but even here two divisions may be recognized — the Protozoa and the Metazoa — the former embracing the single phylum Pro- tozoa, or one-celled animals; the latter, all the rest which agree in consisting of many cells, hav- ing a two-layered embryonic development. HistoRicAi, Sketcti of Ci.assiftcation. The Greeks had considerable knowledge concerning animals, which Aristotle recorded, added to, and arranged, for the first time of which we have any knowledge, in an orderly fashion. Aristotle had some conception of genera and species. It is true that his y4m (ficnns) was a rather elas- tic term, since it was applied both to small and large groups of animals. Aristotle also conceived a dill'erence be. ween vertebrates and inverte- luates, althoigli he made the distinction by means of an erroneous delinition. The following are the eight groups of animals as defined by Aristotle: .Inimiils uith Blood — Vertebrates: (1) Viviparous animals (four-footed), and in a special y4ms (i/t'jios) of this the whale was placed. (2) Birds. (3) Oviparous, four-footed animals. (4) Fishes. .inimuls witlwitt {red) lilood— Invertebrates: (5) Soft animals | yuaXdicta, mo/atio, i.e. Cepha- lopoda). (6) .;Vnimals with soft shells {/juiXa- KlxTTpaKa. mo/oAo.s7r(/A((, i.e. Crustacea). (7) In- sects. (S) Shelled animals (sea-urchins, snails. mussels ). The elder Pliny added little to our knowledge of animals. He Avas simply a compiler, who copied freely from Aristotle, whom he some- times misunderstood, and he admitted much of the error and superstition of his time to rank with fact. It was not until the seventeenth cen- tury that any very great addition to our knowl- edge of the structure, development, and relations of animals was made. LiniKcus to Cuvier. — Kay wrote a Synopsis of Mammalia and Rcplilia (London, 1693), which was used by the master systematizer, Linnceus (1707-78), in his Systema Xatiirw, as the foun- dation upon which he built that part of his clas- sification that had to do with vertebrates. Lin- nteus did not add much to our knowledge as an investigator; but he sifted and sorted, rejected and retained, from the accunuilations of his predecessors, and out of this more or less chaotic mass he erected his orderly system — the first great classification of animals. His Systema Xatiirw went through thirteen editions, twelve of which were published during his lifetime, and five of these were revisions by his own hands. The arrangement by Linnaeus was into 'classes,' as follows: (1) JIannnalia. (2) Aves. (3) Amphibia ( including reptiles). (4) Pisces. ( 5 ) Insects ( including insects proper, myria- pods, arachnids, and crustaceans). (6) Vermes (radiates, mollusks, worms, cirripeds, and a fish, mvxine). This classification was based mainly on exter- nal appearance and some internal anatomy; and, though imperfect and incomplete, it gave a great impulse to the study of zoology and to more orderly arrangements of animals, based on ana- tomical characters. It was Linnteus who intro- duced binary nomenclature, since he first gave every animal a generic and a specific name of Latin origin. The next great systematist was Cuvier (1769- 1832). "Cuvier did not." says Glaus, "as most zoiitomists have done, look upon anatomical dis- coveries and facts as in themselves the aim of his researches: but he contemplated them from a comparative point of view, which led him to the establishment of general principles." Jlore- over, Cuvier appreciated fully the idea of 'corre- lation.' "The organism." he declared, '"consists of a single and complete whole, in which single parts cannot be changed without causing changes in all the other parts." Cuvier became con- vinced, from a study of the nervous system and the arrangement of the systems of organs, that the animal kingdom is divided into four great branches (Tableau I'lrnientairr de I'histoire natu- relle des animaiix, Paris, 1708) as follows: