Chapter IV 

 THE ORDER AMONG ANIMAL TYPES 



The Purpose of Classifying Animals. In the preceding 

 chapters the reader has at his disposal the essentials of the prin- 

 ciples of the structure and of the functioning of protoplasm, its 

 organization into cells, and at least some of the facts of animal 

 organization as exemplified by animals that consist of single cells. 

 He can go no farther intelligently in the application of the prin- 

 ciples already developed and in understanding still other funda- 

 mentals without knowing something of the wide diversity of form 

 among animals. In assembling a body of knowledge, whether it be 

 a history of a human endeavor, a method of manufacture, or an 

 understanding of the application of biological principles and the 

 relation of animals to each other, three steps are involved: One is 

 the discovering of the facts; the second is the placing of these facts 

 in the proper order with reference to each other, the fitting together 

 of the pattern; the third is the analysis of the significance of the 

 pattern revealed when the facts have been fitted together and placed 

 in their proper order. To appreciate the principles of Biology one 

 must first know something of the similarities and dissimilarities 

 among animals and an orderly scale of complexity must be estab- 

 lished. Otherwise one cannot take the second step, that of obtaining 

 a full comprehension of the significance of the facts of animal 

 structure and of animal function. A knowledge of the chief charac- 

 teristics, at least, of the several larger groupings that represent 

 human attempts to indicate the orderly arrangement of animal life 



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