ZOOLOGICAL NOMENCLATURE is the system on which names are given to the various divisions of the animal kingdom. Those divisions range from the great branches or Phyla, through Classes, Orders, and Families, with occasional intermediate groupings, down to Genera and Species. For the meanings of those terms, see ZOOLOGY. It can hardly be said that any system governs the names of categories higher than Fami lies; essentially the existing system relates to genera and species. The system arose in response to three needs : first, to have a name intelligible in all countries; second, to fix on a single name for each kind or species of animal, and thus to avoid the confusion due either to the application of the same name to quite different kinds, or to a multiplicity of names for a single kind (there are 136 English names for the salmon and sea-trout) ; third, to provide names for the many thousands of newly-discov ered species existing now or in past ages, and without a name in any language.
The binary system of nomenclature now in use for animals was first consistently employed in Linnaeus, Systema Naturae, ed. x. (1759). To meet difficulties that arose later, a code of rules, drawn up by H. E. Strickland and a committee, was accepted by the British Association for the Advancement of Science in 1842, and held the field till 1881. Increasing difficulties then led to the promulgation of other codes by various societies and individ uals, until the consequent diversity of practice forced the need for agreement on the notice of the International Congress of Zoology (Paris, 1889), and it requested R. Blanchard to report. The difficulties not having been overcome, the third congress (Leyden, 1895) appointed an international commission with C. W. Stiles as secretary. This eventually submitted a unanimous report at Berlin (Igor) ; the rules were adopted and published by the congress (1902). At subsequent congresses, down to that in Budapest (1927), slight amendments have been made, and the rules as they now stand have been separately issued by the Biological Society of Washington. A series of "opinions" deliv ered by the Commission, interpreting the rules and applying them to doubtful cases, has been published by the Smithsonian Insti tution, Washington.
The basis of the rules is the law of priority : "The name of a genus or species can only be that name under which it was first designated." Nearly all the other rules lay down the conditions
to which the application of this law must conform. Since the rigid application of the law would sometimes lead to confusion, and since the Commissioners sometimes cannot agree whether an author has conformed to the conditions or no, the congress has decided that in rare cases the rules may be suspended and an arbitrary decision given.
The chief difficulty has been that of deciding precisely for what genus or species an author proposed a certain name. Only when an author gives a differential diagnosis, and fixes on a single specimen (holotype) as the standard of his new species, or a single species (genotype) as the standard of his new genus, can subse quent workers be sure of his meaning. These practices are now followed by every competent systematist, and the International Congress has decided that no generic or specific name published after Dec. 31, 193o, shall be valid unless it is accompanied by an adequate descriptive diagnosis and, in the case of a generic name, by the unambiguous designation of a genotype.