THE CLASSIFICATION OF ANIMALS 113 



with the solitary species. Each genus of animals is given a 

 Greek or Latin name, of a single word. Thus the genus 

 including the hairy and downy woodpeckers is called 

 Dryobates; and the genus including the nickers is called 

 Colaptes. But it is necessary to distinguish the various 

 species which compose the genus Colaptes, and so each 

 species is given a name which is composed of two words, first 

 the word which is the name of the genus to which it be- 

 longs, and, second, a word which may be called the species 

 word. The species word of the yellow-shafted nicker is 

 auratus (the Latin word for golden), so that its scientific 

 name is Colaptes auratus. The natural question, Why not 

 have a single word for the name of each species? may be 

 answered thus : There are already known more than 500,000 

 distinct species of living animals; it is certain that there are 

 no less than several millions of species of living animals; new 

 species are being found, described and named constantly; 

 with all the possible ingenuity of the wordmakers it would 

 be an extremely difficult task to find or to build up enough 

 words to give each of these species a separate name. This 

 is not attempted. The same species word is often used for 

 several different species of animals, but never for more than 

 one species belonging to a given genus. And the names of 

 the genera are never duplicated. (There are, of course, 

 much fewer genera than species, and the difficulty of finding 

 words for them is not so serious.) Thus the genus word in 

 the two-word name of a species indicates at once to just 

 what particular genus in the whole animal kingdom the 

 species belongs, while the second or species word distin- 

 guishes it from the few or many other species which are 

 included in the same genus. This manner of naming 

 species of animals and plants (for plants are given their 

 scientific names according to the same plan) was devised by 

 the great Swedish naturalist Linnaeus in the middle of the 

 eighteenth century and has been in use ever since. 



