374 THE CHANGING GENERATIONS 



Latin or latinized words. The first is the name of the genus to which the species 

 belongs; the second, that of the particular species of that genus. The name of the 

 "squirrel" genus is Sciurus (from the Greek, meaning "shadow-tail"); the two 

 species of squirrels mentioned above are Sciurus niger (squirrel, black = fox 

 squirrel) and Sciurus carolinensis (squirrel, living in the Carolinas = gray squir- 

 rel). The "flying squirrel" genus is Glaucomys (Greek, meaning "blue-gray 

 mouse"); the species is Glaucomys volans (gray mouse, flying). The "crow" genus 

 is Corvus (Latin, "crow") ; the two species are Corvus ossifragus (crow, that breaks 

 bones = fish crow) and Corvus brachyrhynchus (crow, with a short beak = com- 

 mon crow). 



This two-name, or binomial, system of nomenclature was the invention of a 

 great Swedish naturalist, Linnaeus. He first used it consistently for plants in his 

 Species Plantarum, published in 1753, and for animals in his Sy sterna Naturae, 

 10th edition, published in 1758. These dates are taken as the starting points in 

 botanical and zoological nomenclature respectively. The use of Latin names was 

 natural at that time, for Latin was then the language of science; but it proved a 

 fortunate choice. Latin has the advantage of being widely understood, and it 

 does not change, since it is no longer a spoken tongue. It has been found necessary 

 to draw up detailed rules to govern the making and use of plant and animal 

 names — the International Codes of Botanical Nomenclature and of Zoological 

 Nomenclature. The most important principle is that the oldest properly estab- 

 lished name is that which must be used. No two genera in the animal or in the 

 plant kingdom may bear the same name, nor can two species of the same genus. 

 The name of the genus is always capitalized, while the second word that desig- 

 nates the species is generally — in zoology always — spelled with a small initial 

 letter. 



The higher taxonomic categories. Starting with the species as the 

 basic unit in classification, we have seen that several or many similar and 

 presumably related species are assembled to form a genus. The genus is a 

 "kind" or category higher and more inclusive than a species. In similar 

 fashion several or many genera may be grouped to form the next higher 

 unit, the family; families are grouped into orders, orders into classes, and 

 classes into phyla. The phylum is the largest division of the kingdom, and 

 the plant and animal kingdoms together comprise all living things. Every 

 species is thus at the same time a member of a genus, a family, an order, 

 a class, a phylum, and a kingdom. 1 



Sometimes these categories are not sufficiently numerous to express all 

 the degrees of relationship that can be distinguished among the species of 

 a given category. In this event additional categories are inserted between 

 the main ones and are designated as sub- or swperspecies, genera, families, 

 orders, etc. If still more categories are needed, they are interpolated into 



1 This is the system that has become established in zoology. Botanists frequently 

 use other names for the categories above the rank of family, although some have 

 proposed systems closely similar to that used in zoology. See Appendix A. 



