GENERAL ZOOLOGY 



the genus Rana and other genera. The genus Rana consists of several closely 

 related species. The relationships of these categories may be shown as follows: 



Order Salientia. 

 Family Ranidae. 

 Genus Rana. 



Species Rana pipiens Schreber, the leopard frog. 



It will be noted that, in referring to the species, it is proper to use both 

 generic and specific names; that is, the name of the animal commonly called 

 the leopard frog is Rana pipiens or R. pipiens, not pipiens alone. The generic 

 name is always capitalized, the specific name always written with a small 

 letter. In the complete form, the name of the species is followed by the name 

 of the individual who originally described it, and the date of the description 

 is given in parentheses. Several of the species making up the genus Rana are 

 R. catesbeiana, the bullfrog; R. clamitans, the green frog; R. sylvalica, the wood 

 frog; R. palustns, the pickerel frog; and R. pipiens, the leopard frog. 



A species containing groups of animals with relatively slight but constant 

 differences is often divided into subspecies or varieties. The amount of 

 difference between the individuals composing any one species can be appre- 

 ciated only by examining a large number of specimens and making compari- 

 sons. In general, the differences that separate subspecies or varieties within 

 species are less than those separating species. Whether a group shall be 

 called a variety of an existing species, described as a new species, or made 

 the basis of a new genus depends on the judgment of the individual making 

 the classification. 



The system of cataloging animals just described illustrates the principles of 

 classification followed at the present time. Beginning with a group of ani- 

 mals, such as a species of frog or grasshopper, we can follow its classification 

 into larger and larger groupings until the phylum is reached, and finally the 

 Animal Kingdom, which is coordinate with the other great group of living 

 things, the Plant Kingdom. Conversely, if we began with the Animal King- 

 dom, we might follow its branches into every subdivision until all the species 

 were reached, and pass in review the diversified known forms of animal life. 

 The modern taxonomic system is the result of years of study, in which 

 hundreds of thousands of species have been described and arranged in 

 accordance with their similarities to other forms. Such a system is necessary 

 as a means of cataloging the multitudinous organisms constituting the 

 Animal Kingdom. 



But classification, as it is now undertaken by biologists, is more than a 

 cataloging system. The basis of classification is structure, and it can be 

 confidently assumed that structural similarities are indicative of ancestral 

 relationships. Since the acceptance of the Theory of Organic Evolution, 

 which followed the publication of Charles Darwin's Origin of Species in 1859, 

 classification has become a never-eading effort to express evolutionary rela- 

 tionships between animals, as well as to furnish a catalog of types. For this 



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