CHAPTER XIII 



CLASSIFICATION OF ANIMALS 



For practical reasons it is necessary to classify the animals of the 

 animal kingdom, listing and arranging them in a definite, orderly, 

 systematic fashion in order that they may be recognized and named. 

 Since there are at least 840,000 different species of animals already 

 described and more being added continually, this becomes signifi- 

 cant. In addition to the matter of convenience in cataloguing ani- 

 mals, our present system of classification, which is based primarily 

 on structures, brings to light many of the phylogenetic relations 

 between groups. The study of classification is called taxonomy, of 

 which some mention has already been made in the introductory 

 chapter. 



The usual method of classification of animals originated with Lin- 

 naeus who lived from 1707-1778. He recognized groups of four dif- 

 ferent values : class, order, genus, and species. Since his time several 

 other divisions of the classification have been added, as the phylum, 

 subphylum, subclass, suborder, family, subfamily, subgenus, and sub- 

 species. The Linnaean system designates the species by two Latin or 

 Latinized names ; the first is the generic name and the second is the 

 specific name. For example, we have Rana catesheiana, the bullfrog, 

 and Rana pipiens, the leopard frog, as two species of frogs belong- 

 ing to the same genus. Because of the necessity for two names for 

 the designation of each species this is known as the binomial system 

 of nomenclature. In cases where subspecies or varieties have been 

 recognized, the genus, species, and subspecies names all are used, 

 making the arrangement trinomial instead of only binomial. 



The basis for our present classification is largely relationship of 

 structure with groups formed because of genetic relation and descent 

 from common ancestry. Animals whose characteristics are similar 

 and whose relationship is evidently very close are placed in the same 

 species. Species which are quite similar are placed in the same 

 genus. Families are each composed of genera which resemble each 

 other in certain respects much more than they resemble other 

 genera. Orders are composed of related families, classes of related 



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