4 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



The artificial character of this and all forms of classification is well 

 seen in the fact that scarcely any two zoologists will agree exactly on 

 the arrangement of the groups. Thus, with regard to the above 

 table, some prefer to raise the three sub-types of Cnidaria, Cleno- 

 phora, and Porifera to the value of Types and to use the word 

 ' ' Ccelenterata ' ' only as an antithesis to that of Codomata. Others 

 regard the grouping expressed by the terms Zygoneura, Ambulacralia, 

 and Chordata as of little value, and would employ the term ' ' Chordata ' ' 

 as the equivalent of Veriebrata (Type VIII), or, again, would reduce 

 the Types VII and VIII of the above table to the rank of sub-types 

 under the Type Chordata. A common usage raises the " Sub-Type II. 

 Arihropoda' ' to the rank of a Type, and unites ' 'Sub-Type I. Annelida' ' 

 to the Vermes (Type III). These differences of individual opinion 

 rest upon the varied emphasis placed upon certain points of structure, 

 or, perhaps, upon convenience to the memory and for purposes of in- 

 struction, and serve but to emphasize the facts that the animal forms 

 available for study are but detached fragments of a once continuous 

 history, and that the position of these fragments is in many cases 

 a doubtful one. 



