256 COMPARATIVE ANATOMY 



these into families ; a family into genera ; and a genus into 

 species. This system of classification and the nomenclature 

 universally used was invented by the great Swedish naturalist, 

 Carl Linnaeus, in the eighteenth century. Before his time there 

 was no system for naming animals, and no recognised subordina- 

 tion of groups into which animals could be placed according 

 to their affinities. Zoology and Botany alike were in confusion, 

 and no progress was possible. The classes, orders, and 

 families established by Linnaeus were arbitrary and artificial, 

 and have been replaced by new groupings as naturalists came 

 to recognise more and more clearly the natural affinities 

 between different animals. But the system of nomenclature 

 introduced by Linnaeus still is and probably always will be in 

 use. The system consists in giving every animal a christian 

 name and a surname. The surname is the name of the genus 

 to which the animal belongs, and, in accordance with the 

 practice of the Latin language, it is put first. The christian 

 name is the name of the species, and it is generally a trivial 

 name alluding to some small peculiarity of the species, or it 

 may commemorate the name of a naturalist or may be alto- 

 gether fanciful. Thus Obelia is the name of the genus, 

 geniculata is the name of the species, given to it because it is 

 bent at every joint like a knee (Latin genu, a knee). A family 

 is a group of closely-allied genera, and is usually named after 

 one of the characteristic genera included in it. Thus the 

 genus Obelia belongs to the family Campanularidae, called 

 after the genus Campanularia closely allied to Obelia. An 

 order is a group of closely -related families, and a class is a 

 group of closely-related orders. This methodical arrangement 

 of groups subordinate to groups has obvious advantages : it 

 assists the memory, enables us to take a general survey of the 

 animal kingdom, and it tells us at a glance what animals are 

 more closely and what more distantly related to one another. 



But the beginner should not forget that a modern system 

 of classification, in which animals are arranged like the 

 divisions, brigades, battalions, and companies of an army, 

 aims at much more than a mere methodical grouping for 

 the sake of precision and convenience. A good classification 

 attempts to arrange animals as far as is possible according 

 to their blood relationships ; in other words, to group them 

 like the branches of a genealogical tree. To use a homely 



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