546 GENERAL CONSIDERATIONS 



confusion as to the correct names of animals. As a consequence some- 

 what more than a half century ago a very strong demand arose for the 

 formulation of a system of rules by which confusion could be avoided. 

 Out of the agitation has developed an International Commission on 

 Zoological Nomenclature the work of which is represented both in a code 

 of rules and in a long series of decisions, involving particular cases, which 

 have been officially promulgated by the Commission, 



According to these rules a family name is made by adding -idae to 

 the stem of the name of a genus selected as the type. Thus the type 

 genus of the cats is Felis and so the family name is Felidae. The name 

 of a subfamily is made in the same way by adding -inae. Whenever for 

 any reason the type genus is changed then the name of the family must 

 be changed accordingly. Generic names must be single words written 

 with a capital letter and specific names either a single or compound word 

 written with a small letter. The generic name is nominative singular in 

 form and the specific name is an adjective in grammatical agreement 

 with it. The author of a name is the first person who definitely attached 

 that name to the particular species. There has, however, been a con- 

 siderable amount of confusion in literature in regard to who first described 

 a given species and also as to whether or not certain species are actually 

 distinct. This makes necessary a decision as to priority and in connec- 

 tion with this matter of priority most of the decisions of the International 

 Commission have been rendered. The best usage in the description of a 

 new species is to designate a particular specimen as a type and to state 

 exactly where the type is to be found and how it is to be recognized. 

 Recognition is usually by some particular number. The commission 

 has not undertaken to make any pronouncement in regard to the names 

 of groups higher than families, and, therefore, the names of the higher 

 groups that any particular writer adopts are evidences of individual 

 opinion. 



620. Phyla. — In earlier chapters of this text the various phyla have 

 been briefly reviewed and the characteristics and advances shown by each 

 noted. It may be well at this point to present a table (Fig. 329) com- 

 paring the characteristics of the different ones. However, two phyla, 

 the Protozoa and the Porifera, are omitted because their plan of structure 

 is so different from that of the rest that they cannot be brought directly 

 into comparison with them. Reading vertically down the columns of 

 this table will furnish an indication of the trends in development of partic- 

 ular characteristics, while reading horizontally will give briefly the 

 characteristics of the individual phylum. 



621. Phylogenetic Tree. — Various diagrams representing a phylo- 

 genetic tree have been presented, reflecting different ideas of the inter- 

 relationships of animal groups. One of the defects of many of these 

 diagrams has been that in spite of the fact that the animal kingdom 



