8 ] The Classification of Lower Organisms 



A fifth principle represents Linnaean practices as subsequently modified: 



5. Named taxonomic groups are necessarily of certain fixed ranks called categories, 

 i.e., lists. There are seven principal categories, specified as follows. Every individual 

 organism belongs to a group conceived as the single kind and called a species. Every 

 species belongs to a genus; every genus to a family; every family to an order; every 

 order to a class; every class to a division or phylum; ever)' division or phylum to a 

 kingdom. These conventions have the effect that the groups of each principal category 

 embrace the entire range of the kinds of organisms. 



The categories of genera and species come down from classic antiquity. Linnaeus 

 originated orders; he originated classes in the sense of named definite groups; and it 

 appears that he is responsible for kingdoms: the writer knows of no earlier authority 

 for the traditional three kingdoms of nature. The category next below that of king- 

 doms has been variously called; originally it was emhranchements (Cuvier, 1812). 

 The history of the category of families is somewhat involved. It originated in the 

 work of Adanson (1763); in the following year, Linnaeus (1764) treated the groups 

 which Adanson had called families as natural orders. Botanists for a long time held 

 that families and orders are the same thing. Zoological practice gradually made fam- 

 ilies a separate category. Authority for the list of seven principal categories as given 

 is Agassiz (1857). 



Nothing prevents the assignment of groups to categories other than these, to sub- 

 classes, tribes, and the like. These may be called subordinate categories. The groups 

 of any subordinate category embrace only fragments of the range of kinds of 

 organisms. 



The work of Linnaeus was largely innovation, and he did not have the face to de- 

 clare binding the generally accepted rule of priority. Definite authority for the rule 

 is de Candolle (1813). As currently applied, it may be stated as follows: 



6. The valid name of a group is its oldest published name, conforming to the rules, 

 and not previously applied in the same kingdom. 



As corollaries of the rule of priority, when groups are combined, the oldest name 

 of any of them must be applied to the whole, and when a group is divided, its name 

 must be retained for one of the parts. The part to which the original name is to be 

 applied is determined by the method of types, formulated by Strickland and his as- 

 sociates (1843) : 



7. When a group is divided, its name must be applied to the portion which includes 

 whatever part of it the original author would have regarded as typical. The part thus 

 specified is the nomcnclatural type of the group. 



In the application of these principles to the naming of the groups of Mychota and 

 Protoctista, the following practices appear expedient. 



A name is applied by publication in such fashion that the community of biologists 

 may reasonably be held responsible for knowing of its existence and recognizing the 

 entity to which it is to be applied. This means that it is to be printed in a technical 

 book or journal and defined in a language for which the generality of biologists will 

 not require an interpreter, namely Latin, English, French, or German. Any regulation 

 more detailed than this is an excuse for breaches of priority. Definition is not neces- 

 sarily by description: nearly all of the Linnaean genera of plants were established 

 by the listing of species in the Species Plantarum. 



When two or more groups published in the same work at the same time are to be 

 combined, their names are of equal priority. The choice of one of their names by the 

 first author who combines them is binding. 



