Survey of the Animal Kingdom 273 



investigator would be unable to know if he were studying a previously 

 described species or if he really had a new one. 



For convenience, the entire animal kingdom is divided into several 

 main groups or phyla (singular, phylum). All the animals included in 

 any particular phylum have certain characteristics in common. These 

 characteristics in the future will be considered as general characteristics 

 in each phylum. 



If our classification were carried no further than phyla, there would 

 be so many differences among the various members that the system would 

 be practically useless. Consequently, all the members of a phylum which 

 have in common one or more arbitrarily chosen characters are placed in 

 a subdivision known as a class. In a similar manner each class is divided 

 into orders, each order into families, each family into genera (singular, 

 genus), each genus into species. The scientific name of any particular 

 animal is composed of its genus and species. For instance, man has the 

 scientific name of Homo sapiens, the former being the genus, the latter 

 the species. 



Approximate Number of Species in the Animal Kingdom 



*Does not include all individuals or groups. 



